Annual Report FY2024

Abstract

The Quantum Engineering & Design unit was recently established in July 2023 beginning with just Bill and his boss Naomi.

As the year progressed, two other talented staff (Oliver, Seungbum and Peizhe) joined us. Our unit explores the design and system engineering of future quantum technologies with the aim to provide a path from today’s theoretical concepts to their real-world implementation.

In particular our focus is on three broad overlapping areas: hybrid quantum systems and their applications, the design of quantum network technologies and distributed quantum computation.

1. MEMBERS

･ Dr. Seungbum Chin, Staff Scientist
･ Dr. Ivan Iakoupov, Postdoctoral Scholar
･ Dr. Heitor Peres Casagrande, Postdoctoral Scholar
･ Dr. Oliver Bellwood, Postdoctoral Scholar
･ Dr. Peizhe Li, Postdoctoral Scholar
･ Hideaki Kawai, Rotation Student
･ Alexandra Berenica Barbosa Gonzalez, Rotation Student
･ Santiago Triana Bejarano, Research Intern
･ Jeonghyeon Song, Research Intern
･ Ms. Naomi Sato, Research Unit Administrator

2. COLLABORATIONS

2.1 Quantum Communication, Repeaters and Networks
   Type of collaboration: Joint Research
   Researchers:
    • Dr Koji Azuma, NTT Basic Research Laboratories (Japan)
    • Dr Hiroki Takesue, NTT Basic Research Laboratories (Japan)
    • Dr Hsin-Pin Lo, NTT Basic Research Laboratories (Japan)
    • Prof Kae Nemoto, OIST (Japan)
2.2 Superconducting Quantum Processors
   Type of collaboration: Joint Research
   Researchers:
    • Prof Xiaobo Zhu, USTC (China)
    • Prof Jian-Wei Pan, USTC (China)
    • Prof Ming, USTC (China)
    • Prof Kae Nemoto, OIST (Japan)
2.3 Hybrid Quantum Systems
   Type of collaboration: Joint Research
   Researchers:
    • Prof Jorg Schmiedmayer, Atominstitut (Austria)
    • Prof Johannes Majer, USTC (China)
    • Prof Kae Nemoto, OIST (Japan)
2.4 Quantum Batteries
   Type of collaboration: Joint Research
   Researchers:
    • Dr James Quach, CISRO (Australia)
    • Dr Josephine Dias (Australia)
    • Dr Arkady Fedorov (Australia)
2.5 Quantum Machine Learning
   Type of collaboration: Joint Research
   Researchers:
    • Prof Kae Nemoto, OIST (Japan)
2.6 Architecture and applications for small to large scale quantum computation [MEXT, Quantum Leap Flagship Program] (Principal Investigator: Kae Nemoto)
   Type of collaboration: Joint Project
   Researchers:
    • Prof Kae Nemoto, OIST (Japan)
    • Prof Mio Murao, University of Tokyo (Japan)
    • Prof Takeaki Uno, National Institute of Informatics (Japan)
2.7 Large-scale distributed quantum computer architecture [JSPS, Grant-in-Aid for Scientific Research(A)] (Principal Investigator: Kae Nemoto)
   Type of collaboration: Joint Project
   Researchers:
    • Prof Kae Nemoto, OIST (Japan)

3.ACTIVITIES AND FINDINGS

3.1 Quantum state processing through controllable synthetic temporal photonic lattices
The first activity is related to photonic quantum computational systems and applications of them which was published in Nature Photonics 19, 95–100 (2025). Quantum walks on photonic platforms represent a physics-rich framework for quantum measurements, simulations and universal computing. Dynamic reconfigurability of photonic circuitry is key to controlling the walk and retrieving its full operation potential. Universal quantum processing schemes based on time-bin encoding in gated fibre loops have been proposed but not demonstrated yet, mainly due to gate inefficiencies. Here we present a scalable quantum processor based on the discrete-time quantum walk of time-bin-entangled photon pairs on synthetic temporal photonic lattices implemented on a coupled fibre-loop system. We utilize this scheme to path-optimize quantum state operations, including the generation of two- and four-level time-bin entanglement and the respective two-photon interference. The design of the programmable temporal photonic lattice enabled us to control the dynamic of the walk, leading to an increase in the coincidence counts and quantum interference measurements without recurring to post-selection. Our results show how temporal synthetic dimensions can pave the way towards efficient quantum information processing, including quantum phase estimation, Boson sampling and the realization of topological phases of matter for high-dimensional quantum systems in a cost-effective, scalable and robust fibre-based setup.

3.2 Quantum key distribution implemented with d-level time-bin entangled photons
The second activity was related to quantum cryptography and in particular quantum key distribution was published in Nature Communications 16, 171 (2025). High-dimensional photon states (qudits) are pivotal to enhance the information capacity, noise robustness, and data rates of quantum communications.Time-bin entangled qudits are promising candidates for implementing high-dimensional quantum communications over optical fiber networks with pro-cessing rates approaching those of classical telecommunications. However, their use is hindered by phase instability, timing inaccuracy, and low scalability
of interferometric schemes needed for time-bin processing. As well, increasing
the number of time bins per photon state typically requires decreasing the
repetition rate of the system, affecting in turn the effective qudit rates. Here,
we demonstrate a ber-pigtailed, integrated photonic platform enabling the
generation and processing of picosecond-spaced time-bin entangled qudits in
the telecommunication C band via an on-chip interferometry system. We
experimentally demonstrate the Bennett-Brassard-Mermin 1992 quantum key
distribution protocol with time-bin entangled qudits and extend it over a
60 km-long optical ber link, by showing dimensionality scaling without
sacri cing the repetition rate. Our approach enables the manipulation of time-
bin entangled qudits at processing speeds typical of standard tele-
communications (10 s of GHz) with high quantum information capacity per
single frequency channel, representing an important step towards an ef cient
implementation of high-data rate quantum communications in standard,
multi-user optical ber networks.

3.3 Exponentially Enhanced Scheme for the Heralded Qudit Greenberger-Horne-Zeilinger State in Linear Optics.
High-dimensional multipartite entanglement plays a crucial role in quantum information science. However, existing schemes for generating such entanglement become complex and costly as the dimension of quantum units increases. In this Letter, we overcome the limitation by proposing a significantly enhanced linear optical heralded scheme that generates the 𝑑-level 𝑁-partite Greenberger-Horne-Zeilinger (GHZ) state with single-photon sources and linear operations. Our scheme requires 𝑑x𝑁 photons, which is the minimal required photon number, with substantially improved success probability from previous schemes. It employs linear optical logic gates compatible with any qudit encoding system and can generate generalized GHZ states with installments of beam splitters. With efficient generations of high-dimensional resource states, our work opens avenues for further exploration in high-dimensional quantum information processing. This work was work published in Phys. Rev. Lett. 133, 253601 (2024).

3.4 Power of Sequential Protocols in Hidden Quantum Channel Discrimination.
In this work published in Phys. Rev. Lett 132, 240805 (2024), we investigated the hidden quantum channel discrimination problem. In many natural and engineered systems, unknown quantum channels act on a subsystem that cannot be directly controlled and measured, but is instead learned through a controllable subsystem that weakly interacts with it. We study quantum channel discrimination (QCD) under these restrictions, which we call hidden system QCD. We find sequential protocols achieve perfect discrimination and saturate the Heisenberg limit. In contrast, depth-1 parallel and multishot protocols cannot solve hidden system QCD. This suggests sequential protocols are superior in experimentally realistic situations.

3.5 Tensor-networks-based learning of probabilistic cellular automata dynamics
Algorithms developed to solve many-body quantum problems, like tensor networks, can turn into powerful quantum-inspired tools to tackle issues in the classical domain. This work focuses on matrix product operators, a prominent numerical technique to study many-body quantum systems, especially in one dimension. It has been previously shown that such a tool can be used for classification, learning of deterministic sequence-to-sequence processes, and generic quantum processes. We further develop a matrix product operator algorithm to learn probabilistic sequence-to-sequence processes and apply this algorithm to probabilistic cellular automata. This new approach can accurately learn probabilistic cellular automata processes in different conditions, even when the process is a probabilistic mixture of different chaotic rules. In addition, we find that the ability to learn these dynamics is a function of the bitwise difference between the rules and whether one is much more likely than the other. This work was published in Phys. Rev. Res. 6, 043202 (2024).

3.6 Experimental demonstration of a Maxwell's demon quantum battery in a superconducting noisy intermediate-scale quantum processor
Entering the era of post-quantum supremacy has given one the ability to precisely control noisy intermediate-scale quantum (NISQ) processors with multiqubits and extract valuable quantum many-body correlation resources for many distinct quantum applications. We here construct quantum many-body thermalized states on a 62-qubit superconducting quantum processor and use them to demonstrate the principle of Maxwell’s demon. We further demonstrate the direct effect caused by Maxwell’s demon on the charging process of a quantum battery (QB). We depicted the nonequilibrium transportation in our QB through measuring the dynamics of the Shannon entropy to explore its working conditions. Finally, we evaluate the information-to-work conversion by varying the readout fidelity to verify the validity of the Sagawa-Ueda equality within the NISQ processor environment and evaluate the qubit-environment interaction such as the measurement backaction. Our experiment suggests that the superconducting NISQ processor with appropriate error mitigation methods will be an ideal platform for studying quantum information thermodynamics through quantum many-body simulations. This work was published in Phys. Rev. A 109, 062614 (2024).

3.7 Performance of Rotation-Symmetric Bosonic Codes in a Quantum Repeater Network
Quantum error correction codes based on continuous variables play an important role for the implementation of quantum communication systems. A natural application of such codes occurs within quantum repeater systems which are used to combat severe channel losses and local gate errors. In particular, channel loss drastically reduces the distance of communication between remote users. Here we consider a cavity-QED based repeater scheme to address the losses in the quantum channel. This repeater scheme relies on the transmission of a specific class of rotationally invariant error-correcting codes. We compare several rotation-symmetric bosonic codes (RSBCs) being used to encode the initial states of two remote users connected by a quantum repeater network against the convention of the cat codes and we quantify the performance of the system using the secret key rate. In particular, we determine the number of stations required to exchange a secret key over a fixed distance and establish the resource overhead. This work was published in Adv. Quantum Technol. 2300252 (2024).

4. PUBLICATIONS

Wan Zo, Seungbeom Chin, and Yong-Su Kim, Heralded optical entanglement distribution via lossy quantum channels: A comparative study, Optics Express 33, 12459 (2025)
Aoi Hayashi, Akitada Sakurai, William J. Munro and Kae Nemoto, Effective quantum feature maps in quantum extreme reservoir computation from the 𝑋𝑌 model, Phys. Rev. A 111, 022431 (2025)
Shin Nishio, Nicholas Connolly, Nicolo Lo Piparo, William John Munro, Thomas Rowan Scruby and Kae Nemoto, Multiplexed Quantum Communication with Surface and Hypergraph Product Codes, Quantum 9, 1613 (2025)
Hao Yu, Stefania Sciara, Mario Chemnitz, Nicola Montaut, Benjamin Crockett, Bennet Fischer, Robin Helsten, Benjamin Wetzel, Thorsten A. Goebel, Ria G. Kr¨amer, Brent E. Little, Sai T. Chu, Stefan Nolte, Zhiming Wang,Jose Azana, William J. Munro, David J. Moss and Roberto Morandotti, Quantum key distribution implemented with d-level time-bin entangled photons, Nature Communications volume 16, 171 (2025)
Seungbeom Chin, Marcin Karczewski, and Yong-Su Kim, Heralded Optical Entanglement Generation via the Graph Picture of Linear Quantum Networks, Quantum 8, 1572 (2024)
Seungbeom Chin, Junghee Ryu, Yong-Su Kim; Exponentially Enhanced Scheme for the Heralded Qudit Greenberger-Horne-Zeilinger State in Linear Optics, Phys. Rev. Lett. 133, 253601 (2024)
Heitor P. Casagrande, Bo Xing, William J. Munro, Chu Guo, and Dario Poletti; Tensor-networks-based learning of probabilistic cellular automata dynamics, Phys. Rev. 6.043202 (2024)
Monika Monika, Farzam Nosrati, Agnes George, Stefania Sciara, Riza Fazili, Andre Luiz Marques Muniz, Arstan Bisianov, Rosario Lo Franco, William J. Munro, Mario Chemnitz, Ulf Peschel and Roberto Morandotti, Quantum state processing through controllable synthetic temporal photonic lattices, Nature Photonics (2024)
Nicolo Lo Piparo, William J. Munro, and Kae Nemoto, Quantum aggregation with temporal delay, Phys. Rev. A 110, 032613 (2024)
Jiale Yu, Shiyu Wang, Kangqiao Liu, Chen Zha Yulin Wu, Fusheng Chen, Yangsen Ye, Shaowei Li, Qingling Zhu, Shaojun Guo, Haoran Qian, He-Liang Huang, Youwei Zhao, Chong Ying, Daojin Fan, Dachao Wu, Hong Su, Hui Deng, Hao Rong, Kaili Zhang, Sirui Cao, Jin Lin, Yu Xu, Cheng Guo, Na Li, Futian Liang, Gang Wu, Yong-Heng Huo, Chao-Yang Lu, Cheng-Zhi Peng, Kae Nemoto, W. J. Munro, Xiaobo Zhu, Jian-Wei Pan and Ming Gong, Experimental demonstration of a Maxwell's demon quantum battery in a superconducting noisy intermediate-scale quantum processor, Phys. Rev. A 109, 062614 (2024)
Sho Sugiura, Arkopal Dutt, William J. Munro, Sina Zeytinoğlu, and Isaac L. Chuang, Power of Sequential Protocols in Hidden Quantum Channel Discrimination, Phys. Rev. Lett. 132, 240805 (2024).
P.-Z. Li, J. Dias, W. J. Munro, P. van Loock, K. Nemoto, and N. Lo Piparo, Performance of Rotation-Symmetric Bosonic Codes in a Quantum Repeater Network, Adv. Quantum Technol. 2300252 (2024).
Hiroo Azuma, William J. Munro, and Kae Nemoto, Heralded single-photon source based on superpositions of squeezed states, Phys. Rev. A 109, 053711 (2024)

5. PRESENTATIONS

William John Munro, Josephine Dias, Hui Wang, Franco Nori and Kae Nemoto, Designing Quantum Batteries, APS Global Physics Summit, Los Angeles, USA, March 16 - 21 (2025)
Heitor Peres Casagrande, Dario Poletti and William Munro, Bath-Driven Quantum Spin Transistor, APS Global Physics Summit, Los Angeles, USA, March 16 - 21 (2025)
Oliver R Bellwood, Ben Powell and Henry Nourse, Raman scattering in quasi-one-dimensional antiferromagnets, APS Global Physics Summit, Los Angeles, USA, March 16 - 21 (2025)
Ivan Iakoupov and William Munro, Matrix-free operators and superoperators for large open-system optimal control in circuit QED, APS Global Physics Summit, Los Angeles, USA, March 16 - 21 (2025)
(Tutorial) William J. Munro, Hybrid Quantum Systems, IEEE EDTM 2025, Hong Kong, March 9 – 12 (2025)
(Invited) Seungbeom Chin, Junghee Ryu, and Yong-Su Kim, Exponentially Enhanced Scheme for the Heralded Qudit Greenberger-Horne-Zeilinger State in Linear Optics, Quantum Information Society of Korea 2025, Seoul, Korea, February 17-19 (2025)
(Invited) William J. Munro, Akitada Sakurai, Aoi Hayashi and Kae Nemoto, Boson sampling powered image recognition, Photonics West 2025, San Francisco, USA, January 25 - 30 (2025)
Heitor P. Casagrande, Bo Xing, William J. Munro, Chu Guo, and Dario Poletti, Tensor-networks-based learning of probabilistic cellular automata dynamics, 8th International Conference on Quantum Techniques in Machine Learning, University of Melbourne, Melbourne, Australia, November 25-29 (2024)
Heitor P. Casagrande, Bo Xing, William J. Munro, Chu Guo, Dario Poletti, Tensor-networks-based learning of probabilistic cellular automata dynamics, AQIS 2024, Hokkaido, Japan, August 26-30 (2024).
(Invited) William J. Munro, Nicolo Lo Piparo and Kae Nemoto, Quantum multiplexing and aggregation in quantum networking, Quantum Communications and Quantum Imaging XXII, SPIE Optics + Photonics, San Diego, USA, August 18 - 22 (2024).
(Invited) Kae Nemoto, Akitada Sakurai, Aoi Hayashi and William Munro, Photonic quantum extreme reservoir computation, Quantum Communications and Quantum Imaging XXII, SPIE Optics + Photonics, San Diego, USA, August 18 - 22 (2024).
Shashank Gupta, Carlos Cid and William Munro, Threshold quantum distillation, Quantum Communications and Quantum Imaging XXII, SPIE Optics + Photonics, San Diego, USA, August 18 - 22 (2024).
Nicolò Lo Piparo, Shin Nishio, William J Munro and Kae Nemoto, All the advantages of quantum multiplexing, 55th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics, Fort Worth, Texas, USA, June 3–7, (2024)
William John Munro, Akitada Sakurai, Aoi Hayashi and Kae Nemoto, Photonic Quantum Extreme Reservoir Computation, CLEO 2024, Charlotte Convention Center, Charlotte, North Carolina, USA, May 05 - 10 (2024)
Stefania Sciara, Hao Yu, Mario Chemnitz, Nicola Montaut, Bennet Fischer, Robin Helsten, Benjamin Crockett, Benjamin Wetzel, Thorsten A. Goebel, Ria G. Krämer, Brent E. Little, Sai T. Chu, Stefan Nolte, William J. Munro, David J. Moss, José Azaña, Zhiming Wang and Roberto Morandotti, On-chip Generation and Processing of Ultrafast Time-Entangled Photonic Qudits for Quantum Communications, CLEO 2024, Charlotte Convention Center, Charlotte, North Carolina, USA, May 05 - 10 (2024)
P.-Z. Li, J. Dias, W. J. Munro, P. van Loock, K. Nemoto, and N. L. Piparo, Quantum Network Utilizing Multiple Channels Based on Cavity-QED and Continuous-Variable Codes, CLEO 2024, Charlotte Convention Center, Charlotte, North Carolina, USA, May 05 - 10 (2024)