Czech-Japan Workshop on Quantum Technologies

27 May 2025, 09:00 → 29 May 2025, 17:50 Europe/Prague

103 (Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague)

Antonín Hoskovec (Department of Physics, FNSPE CTU in Prague), Aurél Gábris (Czech Technical University in Prague), Igor Jex (FNSPE CTU in Prague)

We are excited to invite you to our upcoming conference, featuring distinguished speakers and engaging topics in cutting-edge research fields. Take a look at our programme.

Conference chairs:

• Akira Furusawa, University of Tokyo, RIKEN
• Yutaka Shikano, Tsukuba University
• Radim Filip, Palacký University
• Jozef Lazar, ISI CAS
• Igor Jex, CTU in Prague
• Petr Kavalíř, UWB Plzeň
• Ján Minár, NTC UWB

Organizing Committee:

• I. Jex (chair)
• M. Štefaňák
• A. Gábris
• A. Hoskovec
• I. Yalcinkaya
• J. Novotný
• M. Parýzková
• V. Potoček
• C. Hamilton
• J. Bouda

Topics Covered:

• Quantum Information and Computation
• Quantum Cryptography
• Quantum Optics
• Quantum Sensing and Metrology
• Quantum Simulations
• Emerging Quantum Technologies
• Quantum Thermodynamics

Organizing Institutions:

Supported by:

Other Participating Institutions:

We look forward to your participation!

Image credit: Aurél Gábris.

Tuesday 27 May

09:00 → 09:15 Opening session

09:00 Opening by H.E Mr. Kansuke Nagaoka, Ambassador of Japan to the Czech Republic

Speaker: Kansuke Nagaoka (Ambassador of Japan to the Czech Republic)

09:05 Opening by Envoy for Quantum Technologies

Speaker: Petr Kavalíř (Envoy for Quantum Technologies)

09:10 Welcome by the Dean of FNSPE

Speaker: Václav Čuba (CTU in Prague - FNSPE, Department of Nuclear Chemistry)

09:30 → 10:20 Session 1

09:30 Optical quantum computers with quantum teleportation

We did the first experiment of unconditional quantum teleportation at Caltech in 1998 [1]. Then we did various related experiments like quantum teleportation network [2], teleportation of Schrödinger’s cat state [3], and deterministic quantum teleportation of photonic qubits [4]. We invented the scheme of teleportation-based quantum computing in 2013 [5]. In this scheme, we can multiplex quantum information in the time domain and we can build a large-scale optical quantum computer only with four squeezers, five beam splitters, and two optical delay lines [6]. For universal quantum computing with this scheme, we need a nonlinear measurement and we invented the efficient way [7]. We recently succeeded in the realization [8]. Our present goal is to build a super quantum computer with 100GHz clock frequency and hundred cores, which can solve any problems faster than conventional computers without efficient quantum algorithms like Shor’s algorithm. Toward this goal we started to combine our optical quantum computer with 5G technologies [9]. For the realization of fault-tolerance with our optical quantum computers, we use Gottesman-Kitaev-Preskill (GKP) qubits [10]. We recently succeeded in the generation [11] and invented an efficient way for the generation [12]. We built a real machine of optical quantum computer in Riken and put it on the cloud. We launched a new start-up company OptQC in September, 2024 which is working on building a large-scale neural network based on optical quantum computers.

References
[1] A. Furusawa et al., Science 282, 706 (1998).
[2] H. Yonezawa et al., Nature 431, 430 (2004).
[3] N. Lee et al., Science 332, 330 (2011).
[4] S. Takeda et al., Nature 500, 315 (2013).
[5] S. Yokoyama et al., Nature Photonics 7, 982 (2013).
[6] W. Asavanant et al., Science 366, 375 (2019).
[7] K. Miyata et al., Phys. Rev. A 93, 022301 (2016).
[8] A. Sakaguchi et al., Nature Communications 14, 3817 (2023).
[9] A. Inoue et al., Appl. Phys. Lett. 122, 104001 (2023).
[10] D. Gottesman, A. Kitaev, and J. Preskill, Phys. Rev. A 64, 012310 (2001).
[11] S. Konno et al., Science 383, 6680 (2024).
[12] K. Takase et al., Phys. Rev. A 110, 012436 (2024).

Speaker: Akira Furusawa (The University of Tokyo, RIKEN)

10:00 Continuous-variable quantum passive optical networks

Quantum networks extend quantum communication to multi-user scenarios.
This can be efficiently done by splitting continuous-variable states to
multiple coherent receivers. Such quantum passive optical networks
then enable various bipartite and multipartite quantum communication protocols. We present continuous-variable quantum passive optical networks with different state preparation methods and user trust levels. We also discuss possibility to improve performance and scalability of such networks by means of multiplexing.

Speaker: Vladyslav Usenko (Palacky University Olomouc)

10:20 → 10:50 Coffee break

10:50 → 12:30 Session 2

10:50 NATO and Quantum Technologies

Speaker: Bryan Wells (NATO Chief Scientist)

11:10 Technology background for experimental quantum research at ISI CAS

The Institute od Scientific Instruments, Czech Academy of Sciences dedicates a significant research effort to quantum physics and application oriented quantum technologies. Especially in the field of quantum metrology, dissemination of precise optical frequencies over the fibre-optic network and levitated nanoparticles close to the fundamental quantum state. The research departments and groups also develop a number of highly advanced technologies that are shared over the insitute and are also available for external collaboration and contract research. Most of them are significant for research in quantum technologies. Thus the Institute can be seen as a technology powerhouse able to contribute to quantum research.

Speaker: Josef Lazar (Institute of Scientific Instruments, CAS)

11:40 Unambiguous preparation of Bell pairs

The ability of preparing perfect Bell pairs with a practical scheme is of great relevance for quantum communication as well as distributed quantum computing. I this talk I present a scheme which probabilistically, but unambiguously produces the |Φ+⟩ Bell pair from four copies of qubit pairs initially in the same arbitrary pure quantum state. The same scheme, extended to eight qubit pairs initially in the same, moderately mixed quantum state, unambiguously produces the |Φ+⟩ Bell pair with quadratically suppressed noise. The core step of the proposed scheme consists of a pair of local two-qubit operations applied at each of the two distant locations, followed by a partial projective measurement and postselection at each party, with results communicated classically. While the scheme resembles standard entanglement distillation protocols, it achieves success within just three iterations, making it attractive for real-world applications.

[1] O. Kálmán, A. Gábris, I. Jex, T. Kiss: Unambiguous preparation of Bell pairs arXiv:2402.16752

Speaker: Aurél Gábris (Czech Technical University in Prague)

12:00 Quantum computation and metrology

In quantum computation, high-precision estimate of several quantities, such as observable expectation and amplitude/phase of a quantum state, is an important task. In those estimation tasks, we can achieve the so-called Heisenberg limit in precision, by appropriately using techniques in quantum metrology. In this talk I will present some of those quantum-limited estimation algorithms, particularly showing an algorithm that is depth-tunable and thereby suitable for device implementation.

Speaker: Naoki Yamamoto (Keio University)

14:30 → 16:00 Session 3

14:30 Probing quantum criticalities in cold trapped ion experiments

Trapped cold ions [1] represent perhaps the simplest physical systems able to realize quantum critical phenomena [2] and study them in great detail and experimental control.

We discuss possible experimental realizations of quantum phase transitions (QPT) [3-5] in the ground state [6], as well as a specific novel generalization - the excited-state quantum phase transition (ESQPT) [7] - using a Rabi-type Hamiltonian realized with a single trapped ion (e.g. 40Ca+ or 171Yb+) [8], endowed with a single qubit and a single motional degree of freedom. The model shows QPTs between the 'normal phase', where the qubit and motional degrees of freedom are uncoupled (or weakly coupled) to several 'superradiant phases', with strong coupling of the two degrees of freedom and nonzero phonon population in the ground state [9, 10].

In the first part of the talk, we overview quantum phase transitions studied in diverse physical settings, ranging from nuclear physics, molecular physics, condensed mater physics to quantum optics. We pay particular attention to ESQPTs, which were first identified in the context of collective dynamics of atomic nuclei [11] and later systematically classified in a broad range of physical settings, using different Hamiltonians showing both regular as well as chaotic dynamics [12-14].

Further, we present experimental protocols suitable for experimental detection of QPTs and ESQPTs with trapped cold ions by "slow" and "fast" quenches, respectively. We discuss the appropriate "speed of the quenches", necessary to address either ground state QPTs or ESQPTs, and work out the behaviors of suitable observables (qubit state, phonon number, qubit-phonon entanglement entropy), with attention to mapping the model parameters to the experimental control parameters.

We acknowledge support by Project No. CZ.02.01.01/00/22_008/0004649 “QUEENTEC“ by Ministry of Education, Youth and Sports of the Czech Republic.

Literature:
1. D. Leibfried, R. Blat, C. Monroe, D. Wineland, "Quantum dynamics of single trapped ions", Rev. Mod. Phys. 75, 281 (2003).
2. M.-J. Hwang, R. Puebla and M. B. Plenio, "Quantum Phase Transition and Universal Dynamics in the Rabi Model", Phys. Rev. Let. 115 180404 (2015).
3. J. A. Hertz, "Quantum critical phenomena", Phys. Rev. B 14 1165 (1976).
4. L. D. Carr (Ed.), "Understanding Quantum Phase Transitions", London: Taylor and Francis, (2010).
5. S. Sachdev, "Quantum Phase Transitions", Cambridge: Cambridge University Press, (1999).
6. M.-L. Cai et al., "Observation of a quantum phase transition in the quantum Rabi model with a single trapped ion", Nat. Comm. 12, 1126 (2021).
7. P. Cejnar, P. Stránský, M. Macek, M. Kloc, Journal of Physics A: Mathematical and Theoretical 54, 133001 (2021).
8. P. Obšil et al., "A room-temperature ion trapping apparatus with hydrogen partial pressure below 10-11 mbar", Rev. Sci. Instrum. 90, 083201 (2019).
9. P Stránský, P Cejnar, R Filip, “Stabilization of product states and excited-state quantum phase transitions in a coupled qubit-field system“, Physical Review A 104 (5), 053722, (2021).
10. J. S. Pedernales, I. Lizuain, S. Felice, G. Romero, L. Lamata and E. Solano, “Quantum Rabi Model with Trapped Ions”, Scientific Reports, 5, 15472 (2015).
11. P Cejnar, M. Macek, S. Heinze, J. Jolie, J Dobeš, "Monodromy and excited-state quantum phase transitions in integrable systems: collective vibrations of nuclei", Journal of Physics A: Mathematical and General 39 (31), L515 (2006).
12. P. Stránský, M. Macek, P. Cejnar, "Excited-state quantum phase transitions in systems with two degrees of freedom: Level density, level dynamics, thermal properties", Annals of Physics 345, 73-97 (2014).
13. P. Stránský, M. Macek, A. Leviatan, P. Cejnar, "Excited-state quantum phase transitions in systems with two degrees of freedom: II. Finite-size effects", Annals of Physics 236, 57-82 (2015).
14. M. Macek, P. Stránský, A. Leviatan, P. Cejnar, "Excited-state quantum phase transitions in systems with two degrees of freedom: III. Interacting boson systems", Physical Review C 99, 064323 (2019).

Speaker: Michal Macek (ISI CAS Brno)

14:50 Quantum squeezing of a levitated nanomechanical oscillator

Manipulating the motions of macroscopic objects near their quantum mechanical uncertainties has been desired in diverse fields, including fundamental physics, sensing, and transducers. Despite significant progresses in ground-state cooling of a levitated solid particle, realizing non-classical states of its motion has been elusive. Here, we demonstrate quantum squeezing of the motion of a single nanoparticle by rapidly varying its oscillation frequency. We reveal significant narrowing of the velocity variance to -4.9 dB of that of the ground state via free-expansion measurements. To quantitatively confirm our finding, we develop a method to accurately measure the displacement of the nanoparticle by referencing an optical standing wave. Our work shows that a levitated nanoparticle offers an ideal platform for studying non-classical states of its motion and paves the way for its applications in quantum sensing, as well as for exploring quantum mechanics at a macroscopic scale.

Speaker: Kiyotaka Aikawa (The University of Tokyo)

15:10 Quantum non-Gaussian Optomechanics

Optomechanics studies coherent interactions between electromagnetic
photons and acoustic phonons. To date, experimental optomechanics
operates primarily with quantum Gaussian states that can be obtained
from thermal states by squeezing and classical driving. Preparing
quantum non-Gaussian states in optomechanics opens a way to further
advantages in fundamental science, quantum sensing, and quantum
computation.

Here, we outline strategies to achieve quantum non-Gaussian states of
mechanical oscillators with an emphasis on optically levitated
nanoparticles. We subsequently devise strategies to verify the
non-Gaussian character of the prepared state by optical measurement
without full tomography. We pay special attention to the optimal ways
of quantification of quantum non-Gaussianity.

Speaker: Andrey Rakhubovsky (Palacký University)

15:30 Optomechanics with levitating nanoparticles

Due to their isolation from the environment, optically levitated nanoparticles in ultrahigh vacuum offer a promising experimental platform for sensing the weak force and testing fundamental physics at the boundary between the classical and quantum regimes. This platform uses one or more interacting nanoparticles levitated by laser beams. The typical diameter of a nanoparticle is about a hundred nanometres. This is about three orders of magnitude larger than an atom, the typical quantum object.

By carefully shaping the phase and intensity profiles of the laser beams, it is possible to create almost arbitrary potential wells in which the nanoparticles oscillate. Using laser cooling techniques, the mechanical energy of the particles can be reduced and recent experiments have even reached the ground state of motion - a hallmark of quantum behaviour. Beyond single particle control, interactions between multiple nanoparticles via optical coupling are being actively explored.

Although most of our current experiments remain in the classical regime, significant progress has been made. We have demonstrated non-equilibrium dynamics of individual levitating objects with coupled degrees of freedom, optical interaction between nanoparticles, cooling of their collective modes, and synchronization of their motion. We have also developed experimental protocols for amplifying and squeezing motion states by stroboscopic switching of optical potentials.

This rapidly developing field promises not only fundamental insights into quantum mechanics, but also new platforms for future quantum technologies.

Speaker: Oto Brzobohaty (Institute of Scientific Instruments of the CAS, v. v. i. Královopolská 147 612 00 Brno Czech Republic)

Wednesday 28 May

09:00 → 10:30 Session 1

09:00 Comfortable closed surfaces for quantum walks

We propose a quantum walk model which reflects the embedding of graphs on the surfaces. This proposed quantum walk model converges to a stationary state due to the balance between the inflow and the outflow of the internal graph. We characterize the scattering matrix, which describes the relation between the inflow and outflow, by the underlying embedding of the graph on the surfaces. Moreover, we also characterize the comfortability, which shows how much the energey is stored in the embedding of the graph, is characterized by the orentability of the embedding surfaces.

Speaker: Etsuo Segawa (Yokohama National University)

09:20 Synchronization of discrete qudit unitary evolutions

Quantum phase-locking is typically explored within the framework of continuous time dynamics. In this study, we consider two qudits undergoing the same discrete unitary evolution, driven by the repeated application of a selected unitary gate. Their individual complex evolutions can generally be decomposed into multiple Rabi cycles with initially different phases. We introduce a simple random unitary mechanism designed to asymptotically phase-lock one an arbitrary chosen pair of corresponding qudit Rabi cycles. The structure of all these mechanisms will be presented and we will discuss how they can be combined to asymptotically achieve a predetermined phase pattern between selected pairs of qubit Rabi cycles. This includes the full synchronization of their complex evolutions. Given that the open system dynamics responsible for phase-locking inevitably lead to decoherence, we also discuss the memory effects associated with these mechanisms and explore their potential applications in synchronizing the internal clocks of two quantum walkers.

Speaker: Jaroslav Novotný (FNSPE, CTU in Prague)

09:40 Nonlinear squeezing as directly measurable quantumness

One of the most important questions in quantum physics always was: Which quantum states are sufficiently quantum? This question is gaining even more importance lately, because quantum non-classicality and, more recently non-Gaussianity, have been shown, together with quantum entanglement, to be important resources necessary for quantum advantage. We present a practical quantifier of such quantities in the form of nonlinear squeezing - a variance of specific measurable operator - and discuss its advantages and applications.

Speaker: Petr Marek (Palacky University)

10:00 On Observer-Dependent Description of Quantum State on Identical Particles

The setup of the Einstein-Podolsky-Rosen (EPR) paradox leads to an observer-dependent description of the quantum state from the perspective of quantum information theory. While this problem is initially considered in a single-particle system, it can be extended to a system of many identical particles. We propose an experimental approach to clarify the quantum state description of identical particles. This experimental proposal is applied to the three-particle Aharonov-Bohm effect.

Speaker: Yutaka Shikano (University of Tsukuba)

10:30 → 11:00 Coffee break

11:00 → 12:10 Session 2

11:00 A Unified Framework for Symmetry-Induced Limitations in Quantum Information Processing

Symmetry is a fundamental concept in physics and appears in a wide variety of contexts. Quantum information processing is no exception, with many theorems being well-known, such as the Wigner-Araki-Yanase (WAY) theorem, which imposes limitations on measurements, and the Eastin-Knill theorem, which restricts error correction codes.

In this talk, we give an inequality that captures the trade-off structure between symmetry, irreversibility, and quantum coherence, and show that this inequality can unify and extend the symmetry-induced limitations. The examples of the applications are as follows:
• A unification of the WAY theorem for the measurements, the Eastin-Knill theorem for covariant codes, and the WAY theorem for unitary gates
• The existence of a class of Gibbs-preserving maps that require infinite implementation coherence costs
• A trade-off relationship between measurement time and error in finite-time measurements, implying that zero-error measurements require infinite measurement time.

Speaker: Hiroyasu Tajima (Kyushu university)

11:20 Quantum thermodynamics with quantum information flow: Theory and experiment

Quantum thermodynamics is an active research area bridging quantum information and nonequilibrium statistical physics. A key to characterize universal behaviors of entropy production is the fluctuation theorem, which leads to the second law of thermodynamics in the regime far from equilibrium. The fluctuation theorem in classical systems has been thoroughly studied under various feedback control setups by incorporating classical information contents, which sheds modern light on “Maxwell’s demon” [1]. However, an intriguing situation in quantum systems, such as continuous (or iterative) measurement and feedback, remains to be investigated.

In this talk, I will first present our theoretical results on the generalized fluctuation theorem and the second law under continuous measurement and feedback [2]. The key ingredient is a newly introduced concept to measure quantum information flow, which we call quantum-classical-transfer (QC-transfer) entropy. QC-transfer entropy can be naturally interpreted as the quantum counterpart of transfer entropy that is commonly used in classical time series analysis.

I will then present our recent collaborating work on an experiment [3]. Specifically, we employ a state stabilization protocol involving repeated measurement and feedback on an electronic spin qubit associated with a Silicon-Vacancy center in diamond, which is strongly coupled to a diamond nanocavity. This setup allows us to verify the fundamental laws of nonequilibrium quantum thermodynamics, including the second law and the fluctuation theorem, both of which incorporate QC-transfer entropy as mentioned above. We further assess the reducible entropy based on the feedback's causal structure and quantitatively demonstrate the thermodynamic advantages of non-Markovian feedback over Markovian feedback. These results reveal a fundamental connection between information and thermodynamics in the quantum regime.

[1] J. M. Parrondo, J. M. Horowitz, and T. Sagawa, Nature Physics 11, 131 (2015).
[2] T. Yada, N. Yoshioka, and T. Sagawa, Phys. Rev. Lett. 128, 170601 (2022).
[3] T. Yada, P-J. Stas, A. Suleymanzade, E. Knall, N. Yoshioka, T. Sagawa, and M. Lukin, arXiv:2411.06709 (2024). *: co-first authors

Speaker: Takahiro Sagawa (The University of Tokyo)

11:50 Recurrence of unitary and stochastic quantum walks

Recurrence means a return of the dynamical system to its initial state. Classical result of Polya [1] from 1920’s shows that a random walk on a line and a 2D grid returns to the origin with certainty, while it is transient on higher-dimensional lattices. For quantum walks, detection of recurrence requires partial measurement after each step [2], yielding a conditional quantum dynamics. Combination of measurement induced effects and faster spreading implies that a quantum walk on a line can escape to infinity without ever returning to the origin. We present a demonstration of this behaviour in a photonic time-multiplexing set-up [3], which was done in collaboration with the experimental group of Christine Silberhorn from University of Paderborn. Partial measurements were implemented by deterministic out-coupling by fast-switching EOMs, allowing to address specific time-bins of the optical signal without destroying the coherence of the remaining ones. We also discuss a recent extension of the study of recurrence to quantum stochastic walks [4], which interpolates between quantum and classical walk dynamics. Surprisingly, we find that introducing classical randomness can reduce the recurrence probability --- despite the fact that the classical random walk returns with certainty --- and we identify the conditions under which this intriguing phenomenon occurs.

1. G. Pólya, Math. Ann. 84, 149 (1921)
2. F. A. Grünbaum, et al., Commun. Math. Phys. 320, 543 (2013)
3. T. Nitsche, et al., Sci. Adv. 4, eaar6444 (2018)
4. M. Štefaňák, et al., arXiv:2501.08674

Speaker: Martin Štefaňák (CTU FNSPE)

14:00 → 15:40 Session 3

14:00 Development of analog optical quantum computer at RIKEN

In this presentation, I will talk about a measurement-based optical quantum computer utilising continuous variables. Compared to other quantum computing platforms, this optical quantum computer has several advantages, such as fast clock frequencies, high scalability, room-temperature operation, and compatibility with telecom technology. Our optical quantum computer utilises four optical parametric amplifiers as squeezers, which are combined by a beam splitter network with optical delay lines to generate a large-scale quantum entanglement in the time domain. Quantum computation is performed through measurements on the entanglement. This optical quantum computer is based on analog quantum computation, enabling liner transformations on 101 input modes at a 100 MHz clock frequency. We have also developed a cloud-based system allowing external users to access the quantum computer, as well as a software development kit to enhance usability.
This work has been undertaken as a part of the Moonshot projects (Project manager: Prof Akira Furusawa) in collaboration with University of Tokyo, NTT, and Fixstars Amplify.

Speaker: Hidehiro Yonezawa (RIKEN)

14:30 Implementation of Quantum communication infrastructure in Czech Republic

European Quantum Communication Infrastructure is a major endeavor of the European Commission. From scientific point of view, it is one of the first and largest transfers of technology in the area of quantum technologies. It covers activities of starting quantum industry, related supporting industries, major extremely interdisciplinary planning, and training and negotiation with public service and military, among many other activities.

Speaker: Jan Bouda (Cybersecurity Hub z.u.)

14:50 Demonstration of continuous-variable Einstein-Podolsky-Rosen paradox using pulsed light source

The EPR paradox is an argument regarding the contradiction between the completeness of quantum mechanics and local realism. To experimentally demonstrate the EPR paradox and steering, an ensemble of strongly entangled quantum systems must be generated and, in principle, independent measurements on the ensemble must be performed to show that it is possible to predict the outcome of a measurement beyond the precision allowed by the uncertainty relation. In this talk, we report a demonstration of the EPR paradox and quantum steering both in the frequency domain and in the time domain measurement using pulsed light source.

Speaker: Takuya Hirano (Gakushuin University)

15:20 Experimental noiseless quantum amplification of coherent states of light by multiphoton addition and subtraction

Conditional addition and subtraction of photons represents a crucial tool for optical quantum state engineering and it forms a fundamental building block of advanced quantum photonic devices. In this contribution we report on experimental realization of conditional addition of up to three photons as well as combination of conditional addition of two photons followed by their conditional subtraction. We utilize these operations to generate highly non-classical states of light and implement approximate probabilistic noiseless amplification of coherent states.
Our experiment is based on single-pass optical parametric amplification in a nonlinear crystal pumped by pulsed picosecond laser. The input signal mode is seeded with a coherent state while the idler mode is initially in vacuum state. Interaction in the nonlinear crystal generates correlated photon pairs in signal and idler modes. Detection of m photons in the output idler mode heralds the addition of m photons into the signal mode. To subtract n photons, we insert an unbalanced beam splitter into the path of the output signal beam and condition on detection of n photons in the auxiliary output port of that beam splitter. The experimentally generated states in signal mode are measured by a home-built balanced homodyne detector with 12 dB signal-to-noise ratio and 100 MHz bandwidth.
We have demonstrated the experimental addition of one, two, and three photons to input coherent states with various amplitudes. The resulting highly non-classical m-photon-added coherent states are completely characterized with time-domain homodyne tomography. We experimentally show that the conditional addition of photons realizes approximate noiseless quantum amplification of coherent states with sufficiently large amplitude. We then experimentally implement combination of conditional addition and subtraction of two photons which realizes high-fidelity noiseless amplification of coherent states even for small coherent amplitudes. Our results significantly extend the range of experimentally accessible noiseless quantum amplifiers and pave the way towards the experimental realization of other complex optical quantum operations based on combination of multiple photon additions and subtractions.

Speaker: Jaromír Fiurášek (Univerzita Palackého v Olomouci)

15:40 → 16:10 Coffee break

16:10 → 17:30 Session 4

16:10 Quantum non-Gaussianity, Coherence and Sensitivity

Quantum non-Gaussian coherences are essential for quantum technology with bosonic systems, with already proven sensing and error correction applications. The talk will overview recent theoretical and experimental methods that have opened the door to understanding, controlling and using quantum non-Gaussian coherences at optical, microwave, and mechanical platforms from a genuine quantum nonlinearity in the detection and dynamics of the oscillators. This territory is still challenging to investigate, both theoretically and experimentally. We will present recent achievements, mainly the experimental tests of climbing the hierarchy of finite-rank quantum non-Gaussian photonic and phononic coherences suitable for sensing and error correction. We will complement this with analysing the role of indefinite-rank quantum non-Gaussian superpositions in quantum sensing. The talk will conclude with related results and the following challenges in theory and experiments with genuine quantum nonlinear interactions with light, atoms, mechanical oscillators, and superconducting circuits to stimulate discussion and further development of this advancing and prospective field.

Speaker: Radim Filip (Palacky University Olomouc)

16:40 Nanofiber Cavity Quantum Electrodynamics Systems for Distributed Quantum Computing

Distributed quantum computing, which connects many quantum processing units (QPUs) with small to moderate numbers of qubits into a large-scale quantum network, is a promising approach to realize the large-scale quantum systems required for fault-tolerant universal quantum computing.

Cavity quantum electrodynamics (QED) systems can serve as a platform for such distributed quantum computers, provided that multiple atoms can be strongly coupled to cavities in an individually addressable manner and that these units can be interconnected with minimal losses. We have been developing nanofiber-based cavity QED systems that fulfill these requirements.

In this talk, we will present our experimental work on: a nanofiber cavity QED system with a single trapped atom in the strong coupling regime [1]; the demonstration of coupled-cavity QED, where two nanofiber cavity QED systems are coherently connected in an all-fiber configuration [2,3]; the development of high-finesse nanofiber cavities to achieve high cooperativity [4–6]; and recent progress toward realizing distributed quantum computing with nanofiber cavity QED systems.

References
[1] S. Kato and T. Aoki, Phys. Rev. Lett. 115, 093603 (2015).
[2] S. Kato et al., Nature Communications 10, 1038 (2019).
[3] D. White et al., Phys. Rev. Lett. 122, 253603 (2019).
[4] S. K. Ruddell et al., Opt. Lett. 45, 4875 (2020).
[5] S. Kato and T. Aoki, Opt. Lett. 47, 5000 (2022).
[6] S. Horikawa et al., Rev. Sci. Instrum. 95, 073103 (2024).

Speaker: Takao Aoki (Waseda University)

17:10 Programmable Continuous-Variable Photonic Quantum Computing in the Time Domain

We present our recent advances in time-domain continuous-variable photonic quantum computing [1]. First, we report progress in developing a programmable continuous-variable photonic quantum computing platform. Recently, we integrated non-Gaussian states of light into our platform and demonstrated multi-step quantum gates acting on these states [2]. This advancement marks a significant step toward universal continuous-variable quantum computing. Second, we introduce a programmable quantum light source capable of generating various non-Gaussian states with arbitrary temporal waveforms without modifying its hardware configuration [3]. This flexibility enables the tailoring of optical quantum states for diverse applications, not only strengthening our quantum computing platform but also advancing broader quantum photonic technologies, including quantum sensing and communication.

[1] S. Takeda and A. Furusawa, APL Photonics 4, 060902 (2019).
[2] T. Yoshida et al., PRX Quantum 6, 010311 (2025).
[3] H. Tomoda et al., Phys. Rev. A 110, 033717 (2024).

Speaker: Shuntaro Takeda (The University of Tokyo)

17:30 → 19:30 Poster session: with refreshments

17:30 Generation and Verification of Quantum Non-Gaussian States in Levitated Nanoparticles

Among various macroscopic quantum systems, levitated nanoparticles are unique candidates for investigating macroscopic quantum effects. A breakthrough in this field is achieving the ground state of mechanical motion, which demonstrates unprecedented control over mechanical degrees of freedom and establishes the foundation for advanced quantum state engineering. With ground state cooling capability now realized, the research frontier can advance toward an even more ambitious objective: the deterministic generation of quantum non-Gaussian states.
This work uses pulsed optomechanical interactions combined with nonlinear photon detection techniques to propose experimentally realizable protocols for generating approximate mechanical Fock states and rigorously confirm their quantum non-Gaussianity. Furthermore, we demonstrate the practical application of the generated non-Gaussian states for sensing phase-randomized displacements. Beyond sensing applications, quantum non-Gaussian states provide a valuable tool for investigating fundamental aspects of quantum thermodynamics and macroscopic quantum phenomena.

Speaker: Foroud Bemani (Palacký University)

17:50 Asymptotic phase synchronization in qudit systems

Spontaneous phase synchronization is a riveting ubiquitous phenomenon observed in a great range of both classical and quantum systems. Based on the thorough analysis of the simplest two-qubit case, two major principles of asymptotic synchronization were identified in continuous open systems. Namely, synchronization through decoherence-free subspace preservation and apt combination of symmetric and antisymmetric attractor contributions resulting in synchronized asymptotics. Their generalization to finite-dimensional systems and possible applications to networks with bipartite interactions shall be presented.

Speaker: Daniel Štěrba (FNSPE CTU in Prague)

18:10 Optical parametric amplification for tomography and non-Gaussianity witnessing

Optical parametric amplifiers (OPAs) amplify a single quadrature of a state of light while de-amplifying along the perpendicular direction. The experimentally available amplification levels are so high that the contribution of the perpendicular quadrature in the resulting state becomes negligible. Therefore, by measuring the intensity of the amplified signal, one can gain information about a single quadrature of the initial state without applying traditional homodyning. One can use this information in various ways.

Our team proposed an efficient procedure including an amplification and a displacement step to reconstruct the quadrature distribution of the initial signal [1]. The importance of the displacement step is twofold: it allows the reconstruction of quadrature distributions that are not symmetric about the origin and mitigates the distorting effect of detection noise. One can perform full state tomography by repeating the method for multiple quadrature directions. Assuming that the initial state was phase-independent, that is, its Wigner function only depended on x^2 + p^2, which is often the case, measuring a single quadrature is sufficient for tomography; this has been experimentally demonstrated by Kalash et al. [2]. Compared to standard homodyne measurements, the essential difference is that instead of obtaining a quadrature measurement directly (x), we probe a nonlinear function (x^2). While this nonlinearity introduces some challenges regarding post-processing, we have shown numerically that the proposed procedure reaches the same precision as pre-amplified standard homodyning.

While additive detection noise may seem irrelevant compared to the mean amplified intensity, it can introduce a significant distortion of the estimated quadrature distribution due to the conversion from the quadratic to the linear scale. This fact limits the resolution of the simplest version of the procedure in the vicinity of the origin. This can be overcome experimentally by introducing a displacement to the signal as suggested in [1] or by post-processing. The post-processing correction either has to assume a specific model of the state of interest or the evenness of the quadrature distribution. For the first approach, we examined the model of a heralded single photon and compared different options to estimate its parameters: the individual photon number probabilities of the signal. Assuming its evenness, the second approach replaces the distorted part of the quadrature distribution with an appropriate polynomial using only the measured intensity moments. Despite working with weaker assumptions, we showed numerically that this approach is quite powerful for different lossy Fock states and is accurate enough to estimate the Wigner function in the origin, a witness of non-Gaussianity.

Interestingly, there are also scenarios in which the nonlinearity of the measurement proves to be an advantage instead of a mathematical hurdle to be overcome. For example, Cov(x^2, p^2) cannot be estimated through standard heterodyne detection, while it is readily available in a heterodyne OPA setup. This can be used to estimate the photon number mean and variance for weak signals, which are quite challenging to measure directly without amplification. Without amplification, it is more straightforward to access photon number probabilities in such scenarios (for example, through the Hanbury Brown--Twiss coincidence scheme). The group of Prof. Filip has extensively dealt with deriving practically applicable non-Gaussianity witnesses for this weak signal regime in terms of photon number probabilities [3]. Analogously, we have now derived a witness in terms of photon number mean and variance, which are more readily accessible in an amplified scheme. Intriguingly, this new witness has a broader applicability in terms of signal brightness: instead of a realistic single photon, it is useful for much higher mean photon numbers.

We have examined the practical estimation problems related to Wigner function tomography from parametrically amplified signals. Specifically, we developed different estimation methods applicable to a wide range of realistic scenarios. Furthermore, we proposed an important addition to the existing toolbox for assessing the non-Gaussianity of quantum states, based on photon number moments instead of photon number probabilities. This new witness perfectly suits the line of quadratic measurements under examination. In conclusion, we significantly developed the theoretical machinery to push the limits of the applications of optical parametric amplifiers in signal processing.

[1] É. Rácz, L. Ruppert, and R. Filip, "OPA tomography of non-Gaussian states of light," Quantum Sci. Technol. 9, 045054 (2024)
[2] M. Kalash and M. V. Chekhova, "Wigner function tomography via optical parametric amplification," Optica 10, 1142-1146 (2023)
[3] R. Filip and L. Mišta, "Detecting quantum states with a positive Wigner
function beyond mixtures of Gaussian states," Phys. Rev. Lett. 106, 200401 (2011)

Speaker: Éva Rácz (Palacky University Olomouc)

18:30 Quantum optimal control via polynomial optimization

Quantum optimal control plays a crucial role in the development of quantum
technologies. By optimizing the shape of a control pulse, we can prepare quantum
states needed to initialize algorithms in a quantum computer and implement unitary
operations on the system. However, most currently used optimization methods rely on
gradient-based techniques, which are inherently non-convex and can lead to complex
landscapes where they may get stuck in local minima. We propose QCPOP, a new
approach that reformulates quantum optimal control as a polynomial optimization
problem. This allows us to apply standard polynomial optimization methods to find
global solutions more effectively.

Speaker: Dr Jakub Mareček (Czech Technical University)

18:50 Quantum non-Gaussian high Fock states of light pulses and their superpositions

Generating high Fock states and their superpositions with certifiable quantum non-Gaussian features remains challenging. While conditional methods using Gaussian states are improving, cavity-based atom-light interactions offer an alternative to nonlinear optics, which has been limited to three-photon states. By incorporating optical delay elements, we predict efficient filtering of Fock states up to ten photons (20% success rate) and superpositions (50% success rate for two-photon states), verified via quantum non-Gaussian criteria. We also assess their robustness, bunching behavior, and sensing capabilities for force, noise, and phase estimation.

Speaker: G. P. Teja (Palacky university)

19:10 Cross-talk in continuous-variable quantum passive optical networks

We investigate the integration of Continuous-Variable Quantum Key Distribution (CV-QKD) protocols into passive optical network (PON) architectures, a widely adopted last-mile solution in communication networks. Given the broadcast nature of PONs, we explore the feasibility of CV-QKD protocols that naturally align with this topology, assessing their potential for seamless coexistence and integration. We analyze various protocol modifications aimed at enhancing performance, extending network reach, and increasing user capacity. Specifically, we theoretically evaluate the impact of multiplexing imperfections, such as cross-talk, on system performance. Our findings provide valuable theoretical insights into the practical implementation of CV-QKD in modern telecommunication infrastructures.

Speaker: Ivan Derkach (Palacky University, Olomouc)

19:10 Generation of Autonomous Quantum Resources by Dissipative Quantum Systems

Theory of open quantum systems, i.e., systems coupled to thermal bath(s) in the quantum regime [1] despite of its age still constitutes a vivid research field addressing various aspects of the general question how the dissipative coupling to a bath, which inevitably also brings quantum noise, influences the quantum dynamics of the studied system. The question is particularly important in the context of quantum information setups where quantum resources such as coherence or entanglement should be prevented from the (supposedly) detrimental effects of the noise. However, as it has turned out recently, the sole dissipative coupling of a quantum systems without any further external control (such as driving fields) can, in fact, also be used for generation of such quantum resources, which are then called autonomous. Our poster addresses two complementary situations for generation of quantum resources – autonomous coherence generated by coupling to an equilibrium quantum bath [2,3] and generation of autonomous quantum entanglement in a nonequilibrium setup [4].

References:
1. Ulrich Weiss, Quantum Dissipative Systems, 4th Edition (World Scientific, Singapore, 2012); H.-P. Breuer and F. Petruccione, The Theory of Open Quantum Systems (Oxford University Press, New York, 2002)
2. Giacomo Guarnieri, Michal Kolář, and Radim Filip, Steady-State Coherences by Composite Sys-tem-Bath Interactions, Phys. Rev. Lett. 121, 070401 (2018); A. Purkayastha, G. Guarnieri, M. T. Mitchison, R. Filip, and J. Goold, Tunable phonon-induced steady-state coherence in a double-quantum-dot charge qubit, npj Quantum Information 6, 27 (2020)
3. Artur Slobodeniuk, Tomáš Novotný, and Radim Filip, Extraction of autonomous quantum coherences, Quantum 6, 689 (2022); Synthesizing and multiplexing autonomous quantum coherences, Quantum 8, 1386 (2024)
4. Bradley Longstaff, Michael G. Jabbour, and Jonatan Bohr Brask, Impossibility of bosonic autono-mous entanglement engines in the weak-coupling limit, Phys. Rev. A 108, 032209 (2023)

Speaker: Tomáš Novotný (Faculty of Mathematics and Physics, Charles University)

Abstract_Czech-Japan_May2025_Prague.pdf

19:10 Generation of optical Schrodinger kitten by optimized displacement quantum receivers

The generation of Schrodinger cat states on different platforms is one of the tasks in quantum information science. To this aim, a key role is played by optical cat states, corresponding to superpositions of coherent states with opposite phases, namely $|\psi_{\pm}\rangle= {\cal N}_{\pm} (|\alpha\rangle \pm |-\alpha\rangle)$, $\alpha \in \mathbb{C}$. Although conventional protocols for their generation are based on photon subtraction and photon addition of squeezed vacuum states, cat states also emerge in the context of binary phase-shift-keying discrimination of coherent states. In fact, the optimum receiver that minimizes the decision error probability corresponds to a cat-state measurement, and is practically implemented by the Dolinar receiver, based on feedback conditional displacement operations followed by photon-number resolving (PNR) detection.

By drawing inspiration on the Dolinar setup, we propose a novel scheme for generation of optical cat states by displacement quantum receivers. We design two optimized receivers, with and without the use of feedforward, and prove them, when applied on one branch of a two-mode squeezed vacuum state, to conditionally produce Schrodinger kitten states.
By these receivers, we produce a $n$-th order kitten, corresponding to the $n$-th order expansion in the Fock basis of a targeted cat state, with considerable success probability. In particular, we show feedforward as a powerful strategy to enhance the success probability for small $\alpha$.
Unlike the existing schemes, our proposal provides a scalable method to approximate a given cat state with arbitrary accuracy, at the cost of lowering the resulting success probability.

Speaker: Michele Nicola Notarnicola (Palacký University Olomouc)

19:10 Identifiability of Autonomous and Controlled Open Quantum Systems

Open quantum systems are a rich area of research in the intersection of quantum mechanics
and stochastic analysis. By considering a variety of master equations, we unify multiple views of
autonomous and controlled open quantum systems and, through considering their measurement
dynamics, connect them to classical linear and bilinear system identification theory. This allows
us to formulate corresponding notions of quantum state identifiability for these systems which,
in particular, applies to quantum state tomography, providing conditions under which the probed
quantum system is reconstructible. Interestingly, the dynamical representation of the system lends
itself to considering two types of identifiability: the full master equation recovery and the recovery
of the corresponding system matrices of the linear and bilinear systems. Both of these concepts
are discussed in detail, and conditions under which reconstruction is possible are given. We set the
groundwork for a number of constructive approaches to the identification of open quantum systems.

Speaker: Waqas Parvaiz (Czech Technical University)

19:10 Identifying topological properties of quantum walks using quantum classification algorithms

Discrete-time quantum walks have emerged as a powerful tool quantum computing. It has been recognized that DTQWs can exhibit a plethora of topological phases, which may be exploited in designing applications that are particularly robust against various types of noise and disorder. The ability to determine the topological phase in which the DTQW is in, is one of the essential tasks for any application. The presented project focuses on exploring the possibility of using quantum classification methods to determine the topological phases of DTQWs. The presented materials will cover the development of a method that uses quantum computer implementations for the training. The emphasis of the talk will be on the techniques used in the programming of quantum algorithms in latest Qiskit SDK, their execution of IBM QPUs and hardware aware optimization.

Speakers: Aurél Gábris (Czech Technical University in Prague), Ondrej Kral, Mr Vlastimil Hudeček (Quantum technologies master degree program student)

19:10 Nullifiers for non-Gaussian cluster states

Gaussian continuous variable cluster states showed great potential for scalability. To unlock their full potential and use them in advanced quantum information applications, it is necessary to accompany them with non-Gaussian resources. There is a vast palette of non-Gaussian states and operations. A fundamental example, available
in experiment in a probabilistic regime, is the photon subtraction.
The usual certification of continuous variable Gaussian cluster states is provided by so-called nullifiers. Here we present nullifiers that certify non-Gaussianity in cluster states prepared from photon subtracted
squeezed vacua. When an expectation value of the presented nullifier is below a Gaussian threshold, the cluster state is non-Gaussian. The evaluation can be done solely from homodyne measurement.

Speaker: Vojtěch Kala (Palacký University Olomouc)

19:10 Polarization entangled photon pairs for characterizing optical activity

Measuring optical activity is an important tool for characterizing and identifying various classes of molecules. Many biologically active molecules are chiral and their enantiomers can have dramatically different biological effect. In biological or biomedical context, the samples are o en complex, fragile and photosensitive. Thus, the ability to measure op cal activity under low light intensity is crucial. We are developing a technique for measuring optical activity using polarization entangled pairs of photons. This approach inherently uses low light intensity and leverages the proper es of non-classical quantum states of light. We expect that the sensitivity of the measurement can eventually overcome the limits achievable with traditional sources of light.
We rely on the source of polarization entangled photons which we developed in our laboratory. The source is based on bidirectionally pumped periodically poled KTP crystal in the Sagnac interferometer configuration. It produces the polariza on entangled photons in one of the Bell states. We will employ entanglement-assisted quantum process tomography which benefits from smaller ensemble of quantum states which are necessary to send through the process. This should not only decrease the number of photons interacting with the studied sample but also increase the sensitivity of the
measurement compared to standard quantum process tomography.

Speakers: Albert Pechoč, Ivan Richter (Czech Technical University in Prague, FNSPE), Miroslav Dvořák

19:10 Quantum Buridan’s Ass

The interplay between symmetry and dynamics is central to physics, as well as to other branches of science. An interesting situation arises in decision making when you are offered several equally viable solutions and you are forced to select one. The ensuing delay of the decision is generally known as the Buridan’s paradox. We investigate a sketch of this situation in the context of quantum optical multiports and comment on the role of symmetry in such systems and how physics deals with the dilemma of many options. It is noteworthy that in the simplest form of a quantum Buridan's paradox, the evolution away from the initial state of the system is sped up by quantum interference resulting from the dynamics. However, more fully connected networks can display the frustration of making a decision, familiar from the classical Buridan's paradox. The role of symmetry breaking is analyzed for several cases and implications for the paradox are discussed. Our results have implications for quantum communication networks and other distributed quantum systems.

Speaker: David Chudožilov (Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University)

19:10 Quantum metrology in nonlinear interferometer with feedback

In this paper, we propose a nonlinear interferometer with a feedback loop and explore its efficiency for phase estimation. We analysis two feedback schemes, one where both modes of the interferometer are fed-back into the device and another where only one mode is fed-back. The quantum Fisher information (QFI) for phase estimation in each feedback scheme increases with each feedback loop, and similar to the standard SU(1,1) nonlinear interferometer, phase estimation in this scheme is sensitive to photon loss when the inputs are vacuum state. In terms of resources, we show that, in the low-loss regime, our scheme performs better than standard nonlinear interferometer.

Speaker: Shivani Singh

19:10 Quantum Systems at the Brink

One of the crucial properties of a quantum system is the existence of bound states. While the existence of eigenvalues below the essential spectrum is well understood. They exhibit exponential decay, and their existence is linked to the energy gap. However, the situation at the threshold is much more subtle. There are two challenging problems for the states at the threshold-their existence and asymptotic behaviour. Since the usual methods for addressing these problems need a safety distance to the essential spectrum, they cannot be applied in critical cases, when an eigenvalue enters the continuum.

We present necessary and sufficient conditions for Schrödinger operators to have a zero-energy bound state. Our sharp criteria show that the existence and non-existence of zero-energy ground states depends strongly on the dimension and the asymptotic behaviour of the potential. There is a spectral phase transition with dimension four being critical.

Furthermore, we present a recently developed method to address the decay rate behaviour. As an illustration of the application, we derive sharp upper and lower bounds for the asymptotic behaviour of the ground state of critical helium type systems at the threshold of the essential spectrum. This is the first proof of the precise asymptotic behaviour of the ground state for this benchmark problem in quantum chemistry.

Speaker: Michal Jex

19:10 Search and state transfer between hubs by quantum walks

We investigate search and state transfer between hubs, i.e. fully connected vertices, on otherwise arbitrary connected graph. Motivated by a recent result of Razzoli et al. (J. Phys. A: Math. Theor. 55, 265303 (2022)) on universality of hubs in continuous-time quantum walks and spatial search, we extend the investigation to state transfer and also to the discrete-time case. We show that the continuous-time quantum walk allows for perfect state transfer between multiple hubs if the numbers of senders and receivers are close. In the discrete-time case, we show that the search for hubs is successful, provided that the initial state is locally modified to account for the degree of each individual vertex. For state transfer using discrete-time quantum walk, it is shown that between a single sender and a single receiver, one can transfer two orthogonal states in the same run-time. Hence, it is possible to transfer an arbitrary quantum state of a qubit between two hubs. Finally, we consider the case of transfer between multiple senders and receivers, where we cannot transfer specific quantum states. Nevertheless, a quantum walker can be transferred with high probability in two regimes, either when there is a similar number of senders and receivers or when the number of receivers is considerably larger than the number of senders.

Speaker: Stanislav Skoupý (FJFI CVUT)

19:10 Topology in quantum materials

Topology plays a crucial role in quantum technologies. In topological materials, certain electronic properties are protected by topological invariants. This protection makes their edge or surface states robust against disorder, impurities and deformation. In extension, topology defines entirely new phases and matter and allows for the fabrication of novel quantum materials with unprecedented properties and robustness, also to environmental conditions. In my talk, I will introduce a methodology based on angle-resolved photoemission spectroscopy that allows for the identification and classification of topological materials and show how this enabled us to discover a novel phase of matter - orbital vortex line, a quantum analog of a real-world tornado. Our theoretical and experimental data-based results represent a promising venue for the discovery of novel topological phases with high relevance in fields of spintronics, quantum computing, or low-dissipation electronics.

Speaker: Jakub Schusser (University of West Bohemia)

19:10 Towards quantum cryptography with time and phase encoding

Quantum computing threatens classical cryptographic key distribution, endangering current and past encrypted data. Quantum Key Distribution (QKD) offers a solution through eavesdropping detection based on quantum mechanics, enabling unconditionally secure key exchange. This thesis presents the simulation and experimental implementation of a BB84 QKD system using time-phase encoding in
interconnected asymmetric Mach-Zehnder interferometers (AMZIs). The objective was to construct a practical optical setup with a Red Pitaya STEMlab 125-14 to demonstrate QKD principles at the single-photon level. The integrated AMZI system, with optimized path length and polarization, achieved classical interference visibility of 45.7%. This approached the 50% theoretical maximum, a limit set because only photons traversing complementary short-long or long-short interferometer paths contribute to the phase-dependent interference. Quantum measurements at the single-photon level, using 60 dB signal atenuation and a dedicated photon counter (with the Red Pitaya managing modulation), yielded 32.6% visibility. This confirmed successful quantum interference and single-photon encoding, crucial for the Quantum Bit Error Rate (QBER). A comprehensive simulation modelled the full QKD protocol—from state generation and channel effects to measurement and all post-processing stages. It analyzed noise and eavesdropping impacts on QBER and secure key length, providing a theoretical benchmark for the experiment.

Speaker: Ondřej Čermák

Thursday 29 May

09:00 → 10:30 Session 1

09:00 Electronic structure of type-II Dirac semimetal superconductor 1T-PdSeTe

High-resolution angle-resolved photoemission spectroscopy (ARPES) using synchrotron radiation is a powerful and versatile technique for elucidating electronic properties such as energy band dispersion, Fermi surface shape, and spin polarization. In our research institute, we operate a compact electron storage ring (HiSOR) for high-resolution ARPES experiments in the vacuum ultraviolet region.

In this talk, we present an ARPES study of the surface and bulk electronic states of the type-II superconducting Dirac semimetal 1T-PdSeTe [1].

The superconducting transition temperature Tc = 3.2 K was almost twice as high as Tc = 1.6 K in 1T-PdTe$_2$. Scanning transmission electron microscopy measurements revealed homogeneously mixed Se and Te atoms in the chalcogen layers in 1T-PdSeTe. While the crystal symmetry is the same (CdI$_2$-type), the lattice constants of 1T-PdSeTe are 3.5% smaller than those of 1T-PdTe$_2$. Our density functional theory calculations on a supercell with mixed chalcogen atoms showed that the overall band structures were similar to those of 1T-PdTe$_2$. We have also confirmed the surface states on 1T-PdSeTe, which are very similar to those on 1T-PdTe$_2$. These results suggest that the lattice symmetry dictates the band dispersion, regardless of the atomic disorder in the chalcogen layers.

Since the electronic band dispersion and local structures were preserved upon substitution, the enhancement of Tc is likely related to the chemical pressure. Our results provide insight into the effects of the solid solution on the surface and bulk electronic states as well as the superconducting transition temperature.

[1] Yogendra Kumar, Shiv Kumar, Venkateswara Yenugonda, Ryohei Oishi, Jayita Nayak, Chaoyu Chen, Ravi Prakash Singh, Takahiro Onimaru, Yasuyuki Shimura, Shin-ichiro Ideta, and Kenya Shimada: Electronic states in superconducting type-II Dirac semimetal: 1T-PdSeTe, Physical Review Research 7, 013174 (2025).

Speaker: Kenya Shimada (Research Institute for Synchrotron Radiation Science, Hiroshima University)

09:30 Quantum Materials and Magnetic Phenomena Studied by Spin-Resolved ARPES: Theoretical perspectives

Quantum materials exhibit a complex interplay between electronic correlations, topology, and magnetism, placing them at the forefront of condensed matter physics and quantum technology. Understanding these systems requires disentangling spin-orbit coupling, electron-electron interactions, and magnetic fluctuations under realistic conditions, including finite temperatures and structural disorder. Spin- and time-resolved angle-resolved photoemission spectroscopy (STARPES) is a crucial technique for probing electronic and spin structures in magnetic and topological materials. However, quantitative interpretation of spin-ARPES data necessitates advanced theoretical models that accurately capture electronic states, spin textures, and dynamic responses to external fields.
I will present a theoretical framework based on the fully relativistic multiple-scattering Green function KKR method [1], effectively modeling spin-dependent photoemission. This approach includes correlation effects via dynamical mean-field theory (DMFT) [2] and describes spin fluctuations using the alloy analogy model [3]. I will also discuss advances in calculating light-induced electronic excitations [4], highlighting their relevance to spin-ARPES studies of topological and magnetic quantum materials.
A novel application is the one-step model of photoemission in studying altermagnets and kagome magnetic materials. Altermagnets, exhibiting unconventional time-reversal symmetry breaking without net magnetization, are explored in RuO2 and MnTe [5,6]. Spin-ARPES combined with the one-step model provides insights into lifted Kramers spin degeneracy, revealing their potential for spintronics. In kagome magnetic materials, persistent flat band splitting and selective band renormalization are observed in FeSn thin films [7], highlighting unique correlation effects and topological phenomena. These developments offer a comprehensive framework for exploring magnetic phenomena and spin dynamics in complex quantum materials.
References:
[1] H. Ebert et al., Rep. Prog. Phys. 74, 096501 (2011). DOI 10.1088/0034-4885/74/9/096501
[2] J. Minár, J. Phys.: Condens. Matter 23, 253201 (2011). DOI: 10.1088/0953-8984/23/25/253201
[3] J. Minár et al., Phys. Rev. B 102, 035107 (2020). DOI: 10.1103/PhysRevB.102.035107
[4] J. Braun et al., Physics Reports 749, 1 (2018). DOI: 10.1016/j.physrep.2018.02.007
[5] J. Krempaský et al., Nature 626, 517 (2024). DOI: 10.1038/s41586-023-06907-7
[6] O. Fedchenko et al., Sci. Adv. 10, eadj4883 (2024). DOI: 10.1126/sciadv.adj4883
[7] Z. Ren et al., Nature Communications 15, 9376 (2024). DOI:0.1038/s41467-024-53722-3
Acknowledgements
I would like to thank the Quantum Materials for Sustainable Technologies (QM4ST) project with Reg. No. CZ.02.01.01/00/22_008/0004572, cofunded by the ERDF as part of the MŠMT.

Speaker: Jan Minar (NTC, University of West Bohemia, Plzen)

10:00 Diamond spin qubit quantum technology: fundaments, fabrication and applications

Electron spin qubits offer a promising platform for solid-state quantum computing and quantum sensing devices based on dipole-dipole entangled states. As concerns sensing, diamond outperforms other quantum materials as concerns the sensitivity and spatial resolution at ambiance. However, the maturity of NV centre technology for quantum computing remains relatively low, primarily due to a central challenge in the field: engineering dipole-dipole coupled NV spin qubits and addressing and reading them individually.

In this presentation, we report on the diamond spin qubit technology, including the diamond crystal growth and NV engineering for the realization of single and strongly coupled NV spin qubits, characterized under ambient conditions. Both Optical Detection of Magnetic Resonance (ODMR) and Photoelectrical Detection of Magnetic Resonance (PDMR) spin state readout techniques were employed [1,2]. Using Double Electron-Electron Resonance (DEER), we verified NV-NV pair formation and extracted key coupling parameters. Also, DEER measurements also allowed us to study the material purity in terms of additional impurities.

We address quantum state tomography for electron spin qubits as well as nuclear spin qubits, evaluated using two-qubit gates. We give also examples of recent sensing applications using quantum magnetometry.

[1] P. Siyushev wet al, Science, 2019, Vol 363, Issue 6428, pp. 728-731 DOI: 10.1126/science.aav2789
[2] M. Gulka, Nature Communication, 12, 4421 (2021)

Speaker: Milos Nesladek (University Hasselt, Belgium and Faculty Biomedical Engineering, Czech Technical University, Kladno, náměstí Sítná 3105, 272 01 Kladno 1, Czechia)

10:30 → 11:00 Coffee break

11:00 → 12:20 Session 2

11:00 AichiSR for Materials Science

Electromagnetic radiation plays a pivotal role in the investigation of material properties. Its interaction with matter varies significantly depending on the wavelength, and different regions of the spectrum are accordingly referred to by distinct names. Synchrotron radiation, characterized by its broad spectral range—from the infrared to hard X-rays—stands out as a revolutionary light source. Thanks to its unique features, such as high brilliance, tunability, and polarization control, it has been hailed, alongside the laser, as one of the two most significant inventions in photonics in the latter half of the 20th century. In particular, in the vacuum ultraviolet to X-ray region, where previously only discrete energy levels were accessible, synchrotron radiation has emerged as a “dream light,” enabling transformative advances in materials science.
　Aichi Prefecture is renowned for its robust manufacturing sector, encompassing transportation machinery, electrical machinery, steel, and production equipment. In FY2023, the value of industrial shipments from Aichi exceeded that of the second-ranked Osaka Prefecture by more than twofold. For 47 consecutive years since 1977, Aichi has played a leading role in Japan’s economy, particularly in key industries such as automotive, aerospace, and robotics. As a central hub of Japan’s manufacturing capabilities, the region continues to drive economic growth and technological innovation.
　To achieve a sustainable society and further enhance high-value-added manufacturing, the development of cutting-edge research infrastructure is essential. The Aichi Synchrotron Radiation Center (AichiSR), established as a core facility within the “Knowledge Hub Aichi” initiative, exemplifies a collaborative framework involving industry, academia, and government. With a focus on industrial applications, AichiSR was designed to strengthen industrial competitiveness and support innovation in manufacturing technologies.
　Reflecting the shared vision of academic and industrial stakeholders, the light source was built around a 1.2 GeV storage ring with a booster ring for top-up operation. It is equipped with four superconducting bending magnets (superbends) for hard X-ray generation, eight normal-conducting bending magnets (normal-bends) for soft X-rays, and an undulator for vacuum ultraviolet (VUV) radiation. The total construction cost of 7.2 billion Japanese yen was funded by Aichi Prefecture (50%), private-sector donations (20%), and the Japanese government (30%).
　Currently, AichiSR operates twelve beamlines, offering a wide range of advanced analytical techniques, including X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and photoelectron spectroscopy. These beamlines are actively used for industrial applications across various sectors, including automotive, semiconductors, ceramics, and energy. For example, local structural analysis of metal alloys contributes to the development of lightweight automotive components, while in situ XAFS and XRD are used to investigate electrode materials in secondary batteries. Through such applications, AichiSR plays a vital role in advancing industrial R&D. Specific examples from AichiSR will also be introduced during my presentation.

Speaker: Toshihiro Okajima (Aichi Synchrotron Radiation Center)

11:20 Thin, Tunable, and Quantum: Exploring 2D Materials for Next-Generation Quantum Technologies

Quantum technologies promise to revolutionize fields ranging from secure communication to ultra-sensitive sensing and high-performance computing. At the heart of these developments lie quantum materials—systems in which quantum effects such as entanglement, coherence, and topological order dominate the physical behavior.

Among them, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides, and van der Waals heterostructures offer unparalleled tunability and novel phenomena, making them ideal platforms for probing quantum effects and engineering the next generation of quantum-enabled technologies. Exploring quantum behavior in van der Waals systems opens new pathways to understand and manipulate exotic phenomena, from topological states to strongly correlated electrons, with far-reaching implications for quantum computing and sensing.

In this talk, I will introduce the current landscape of quantum materials research, with particular emphasis on 2D systems, their unique properties, and their integration into emerging quantum technologies. Next, I will discuss how these materials serve as platforms for investigating fundamental quantum phenomena and enabling applications ranging from spintronics to quantum light sources.

Special attention will be given to recent and ongoing research efforts at Charles University [1], where interdisciplinary teams are advancing our understanding of low-dimensional quantum systems through a combination of theoretical modeling, materials synthesis, and cutting-edge characterization techniques. The talk aims to illustrate both the scientific significance and the transformative potential of quantum materials research in the broader context of the quantum technology ecosystem.

[1] https://www.mff.cuni.cz/en/quantum-technologies

Speaker: Jana Kalbáčová Vejpravová (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

11:40 Ultrafast quantum dynamics revealed with photoelectron spectroscopies

When an electron is ejected via the photoelectric effect, the emission is not instantaneous but occurs with attosecond (10^-18 s) time delays. These photoemission time delays contain essential information on the attosecond dynamics of electron correlation, screening, and phase shifts, and their measurement has become possible with the advent of attosecond science. Such measurements are expected to provide new insights into the electronic structure and light–matter interactions in quantum materials, contributing to the understanding of their electronic properties and ultrafast optical responses. Recent studies have highlighted the relevance of zeptosecond (10^-21 s) scale effects, particularly non-dipole contributions related to light propagation between atoms.
In this work, we present a theoretical analysis of core-level photoemission time delays in diatomic molecules within the framework of Multiple Scattering theory. Furthermore, we extend our theoretical model to incorporate the effect of intra-molecular light propagation, enabling us to discuss zeptosecond non-dipole contributions to the photoemission time delays.

Speaker: Keisuke Hatada (Department of Physics, University of Toyama)

12:00 Interface Control by Fe buffer Layers in FeSe/MgO heterostructure

The last decade witnessed the growing interest in thin film growth of iron-based superconductor FeSe, because of its strong flexibility in electronic band structure and electronic properties via stoichiometry, strain and doping. This is largely beneficial, in particular for electronic-device applications such as Superconducting Quantum Interference Device (SQUIDS) and bolometer detectors, where a reduced thickness is imperative for achieving high sensitivity and realizing applications in the THz frequency regime (e.g. for astronomical investigations). The strong fascination exerted by FeSe demands reliable engineering protocols for a reproducible growth of FeSe with defined properties and effective approaches towards inducing superconductivity in FeSe thin films. At present, the growth of ultrathin FeSe films using pulsed laser deposition (PLD) demands the control of the chemical composition at the film/substrate interface. Due to the volatile nature of Se, the PLD process has a tendency in producing Fe-rich films. Our study focuses on the film/substrate interface, the tendency for domain matching epitaxial growth, and the disadvantage of chemical heterogeneity. We propose that homogenization of the film/substrate interface by Fe buffer layers enables the control of film stoichiometry and epitaxial film growth in a way that they favor the emergence of superconductivity even in ultrathin FeSe films grown by PLD. Lastly, we report the recent progress in our studies on Mn/FeSe heterojunctions, in which long-range superconducting proximity effect is expected to emerge.

Speaker: Yukiko Obata (Department of Material Chemistry, Kyoto University)

14:30 → 16:00 Session 3

14:30 Overheads scaling in large-scale fault-tolerant quantum computation

Fault-tolerant quantum computation (FTQC) is a method of protecting computing steps from errors which occur continually due to faults in the physical devices. One of the important questions toward the realization of a large-scale quantum computer is the overheads of FTQC, namely, how much increase one should pay in terms of space and time to fight against errors and what is the best structure of FTQC to reduce the overheads. The earliest proposal of FTQC achieving a threshold theorem was based on concatenated codes. Tiny error correcting codes to protect a single logical qubit is nested again and again to protect it against many physical errors. In contrast to this early approach, the recent research trend considers a single ‘big’ code, such as a surface code and more generally a quantum LDPC code, to protect against many errors. The latte approach has a striking feature that one can increase the number of logical qubits as the size of the code, leading to a constant space overhead. In this talk, I will discuss our recent progress in both approaches. We were able to prove threshold theorems even when we include the scaling of classical computation time used in the execution of FTQC protocols. For concatenated codes, we showed that a constant space overhead is also achievable in this approach by using a series of small codes protecting multiple logical qubits rather than a single one. For LDPC codes, we drastically improved its time overhead scaling to lift the apparent trade-off relation between space and time overheads. We believe that our new findings have shed a new light on the discussion on various FTQC methods in terms of efficiency for large-scale quantum computation.
This work was supported in part by JST [Moonshot R&D][Grant Number JPMJMS2061].

Speaker: Masato Koashi (Univ. of Tokyo)

15:00 Quantum Enhanced Artifical Intelligence

Overview of current state of IBM Quantum computers, what are current limitations for use in the field of artificial intelligence and how to overcome them. Referring to some of the promising work done in that field and what are preliminary results from Motol Hospital in the Czech Republic.

Speaker: Ondrej Kral (IBM Czech Republic)

15:20 Quantum Computing Methods for Malware Detection

We focus on applying Quantum Support Vector Machine (QSVM) to malware detection, framed as a binary classification problem, aiming to distinguish two classes of samples: malicious and benign (harmless) software. In our recent work, we implemented and trained the QSVM model and evaluated its performance on both the simulator and quantum hardware from IBM. We found that QSVM consistently achieves higher or comparable accuracy than a classical benchmark (SVM with various kernels). This suggests the capability of QSVM to extract more information from limited data than classical SVM.

Speaker: Eliška Krátká (FIT CTU)

15:40 Recent advances towards early fault-tolerant quantum computing

A coming era of quantum computing is called early fault-tolerant quantum computing, which is expected to be equipped with error corrected logical qubits surpassing the life time of physical qubits.
In our talk, we first overview what are interesting open questions, and then proceed to introduce some of our works that make the first step to resolve them.
Specifically, we introduce our work on resource estimation for the earliest practical quantum advantage in condensed matter physics [1], and then proceed to discuss how to counteract errors (on top of error correction) in early FTQC regime [2, 3].
[1] NY, Okubo, Suzuki, Koizumi, Mizukami, npj Quantum Information 4, 45 (2024).
[2] NY, Akibue, Morisaki, Tsubouchi, Suzuki, arXiv:2405.15565.
[3] Tsubouchi, Mitsuhashi, Sharma, NY, arXiv:2405.07720.

Speaker: Nobuyuki Yoshioka

16:00 → 16:30 Coffee break

16:30 → 17:40 Session 4

16:30 Toward Practical Quantum Computing: Meeting the Challenges

We are actively pursuing quantum computing to address societal challenges intractable for conventional computers. We are committed to research and development (R&D) across all layers of quantum computing, from quantum devices to algorithms and applications.

We are developing superconducting qubit technology with RIKEN. In October 2023, we launched a 64-qubit superconducting quantum computer at the RIKEN RQC-Fujitsu Collaboration Center [1]. Moreover, we have recently developed a 256-qubit superconducting quantum computer [2], demonstrating the scalability of our qubit-chip design. The presentation will briefly discuss our efforts to improve the uniformity in qubit characteristics [3] and to build the large-scale systems.

Our collaboration at TU Delft aims for the development of quantum computers using the diamond-spin qubit technology. We utilize electron spins formed at tin-vacancy (SnV) centers in diamond as qubits [4]. ¹³C nuclear spins near SnV centers are also used as qubits. In this technology, since SnV qubits can be entangled using photonic interconnect, there is freedom in the topology of qubit connections. This may enable the implementation of a new quantum error correction code for our diamond spin qubits, potentially reducing the overhead for quantum error correction in the future.

Our collaboration with Osaka University focuses on fault-tolerant quantum computing (FTQC) software, including error correction [5] and logical gate operations. We have recently proposed a novel quantum computing architecture that incorporates error correction [6, 7]. This "partially" fault-tolerant quantum computing approach aims to significantly reduce the number of qubits and gate operations required for practical quantum computing.

This presentation provides a concise overview of Fujitsu's comprehensive quantum computing research.

References
[1]https://www.fujitsu.com/global/about/resources/news/press-releases/2023/1005-01.htm
[2] https://www.fujitsu.com/global/about/resources/news/press-releases/2025/0422-01.html
[3] T. Takahashi, et. al., Jpn. J. Appl. Phys. 62, SC1002 (2023).
[4] M. Pasini et al., Phys. Rev. Lett. 133, 023603 (2024).
[5] J. Fujisaki, et al., Phys. Rev. Research 4, 043086 (2022).
[6] Y. Akahoshi, et al., PRX Quantum 5, 010337 (2024).
[7] R. Toshio, et al., Phys. Rev. X in press, arXiv:2408.14848 (2024).

Speaker: Shintaro Sato (Fujitsu Limited)

17:00 Building superconducting quantum computers with tileable qubit architecture

This year marks a centenary of quantum mechanics that essentially began with Werner Heisenberg's formulation of matrix mechanics in 1925. Quantum mechanics emerged as a description of the microscopic world of atoms not directly accessible by humans living in the macroscopic world. Nonetheless, over the years, it has become possible to observe and even control quantum mechanical properties in micron-scale, man-made solid-state devices. It is a quarter century ago that coherent control of a superconducting device called a Cooper-pair box, or an artificial atom, was first demonstrated, triggering worldwide research on superconducting quantum bits (qubits). Consecutive efforts to improve design, materials, qubit coherence, and control fidelity since then have led to a recent dramatic increase in the number of available qubits. One of the key challenges for scalable qubit architecture is how to deliver microwave signals to the individual qubits that are just a few hundred microns apart in a two-dimensional chip. To address this issue, we adopt a tileable square-lattice qubit architecture with the coaxial cables addressing the backside of the chip from the vertical direction. In this talk, I will discuss the chip design, three-dimensional integrated wiring and performance of integrated chips of superconducting quantum computers being developed at RIKEN Center for Quantum Computing.

Speaker: Eisuke Abe (RIKEN)

17:20 Benchmarking quantum devices beyond classical capabilities

Rapid development of quantum computing technology has led to a wide variety of sophisticated quantum devices. Benchmarking these systems becomes crucial for understanding their capabilities and paving the way for future advancements. The Quantum Volume (QV) test is one of the most widely used benchmarks for evaluating quantum computer performance due to its architecture independence. However, as the number of qubits in a quantum device grows, the test faces a significant limitation: classical simulation of the quantum circuit, which is indispensable for evaluating QV, becomes computationally impractical. In this work, we propose modifications of the QV test that allow for direct determination of the most probable outcomes (heavy output subspace) of a quantum circuit, eliminating the need for expensive classical simulations. This approach resolves the scalability problem of the Quantum Volume test beyond classical computational capabilities.

Speaker: Ryszard Kukulski (IT4Innovations National Supercomputing Center)

17:40 → 17:50 Closing remarks

Speaker: Igor Jex (FNSPE CTU in Prague)