Superconducting Quantum Computers
Superconductivity is a quantum phenomenon in which electrical resistance becomes zero, manifesting on a macroscale that is visible to the human eye.
By using a superconductor to create an LC resonator, which consists of an inductor L and a capacitor C, a resonator can be created with extremely low loss. The Josephson junction, which consists of a thin insulator sandwiched between superconductors, behaves as a nonlinear inductor due to the quantum tunneling effect of Cooper pairs. Application of this junction enables the creation of an artificial atom that has discrete energy levels with non-uniform gaps.
The atom–atom interactions and atom–electromagnetic wave (microwave) interactions of these huge artificial atoms are much stronger than the atom–atom interactions and atom–electromagnetic wave (light) interactions of regular atoms. These are a feature of superconducting circuits with low loss characteristics.
Toshiba is conducting research and development aimed at realizing quantum computers that utilize this characteristic of superconducting circuits. To this end, the company has previously proposed:
- Kerr parametric oscillator, which can create a Schrödinger’s cat state through the quantum bifurcation phenomenon, using the nonlinearity of Josephson junctions;
- Quantum bifurcation machine, which uses the Kerr parametric oscillators as fundamental elements and can be used as either an annealing-type or gate-type quantum computer; and
- Double-transmon coupler, which is a tunable coupler that can adjust the strength of the coupling between superconducting quantum bits and solve the problems of conventional methods of tunable coupling.
Circuit diagram of two fixed-frequency transmon qubits coupled with a double-transmon coupler
Research News
Quantum-Inspired Computing: Simulated Bifurcation Machine
Classical models of quantum bifurcation machines can be described by the Hamiltonian equations of motion in classical mechanics.
Simulated bifurcation algorithms are a method for solving combinatorial optimization problems by transforming these equations so that they can be simulated quickly by numerical computations and solving using the symplectic Euler method, which is a simple and stable method of solving numerical problems. Simulated bifurcation machines are a high-speed implementation that uses cutting-edge parallel processors such as FPGAs and GPUs.
Although the principles of simulated bifurcation machines are expected to be built on the classical bifurcation phenomenon and classical adiabatic theorem—because the principles of quantum bifurcation machines are built on the quantum bifurcation phenomenon and quantum adiabatic theorem—there remain many unknowns.
Research is now under way with the aim of understanding these principles and improving performance. Toshiba is also developing pioneering applications that utilize the speed and flexibility of these machines.
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Research News
Publications
2025
High-performance conditional-driving gate for Kerr parametric oscillator qubits
Hiroomi Chono and Hayato Goto
APL Quantum 2, 016110 (2025)
2024
Realization of high-fidelity CZ gate based on a double-transmon coupler
Rui Li, Kentaro Kubo, Yinghao Ho, Zhiguang Yan, Yasunobu Nakamura, and Hayato Goto
Physical Review X 14, 041050 (2024)
High-performance multiqubit system with double-transmon couplers: Toward scalable superconducting quantum computers
Kentaro Kubo, Yinghao Ho, Hayato Goto
Physical Review Applied 22, 024057 (2024)
Fast elementary gates for universal quantum computation with Kerr parametric oscillator qubits
Taro Kanao, Hayato Goto
Physical Review Research 6, 013192 (2024)
Ultra-High-Speed Optimization for 5G Wireless Resource Allocation by Simulated Bifurcation Machine
H. Obata, T. Nabetani, H. Goto, K. Tatsumura
Proc. of IEEE Wireless Communications and Networking Conference (WCNC) (2024)
Efficient and Scalable Architecture for Multiple-chip Implementation of Simulated Bifurcation Machines
T. Kashimata, M. Yamasaki, R. Hidaka, K. Tatsumura
IEEE Access 12, 36606-36621 (2024)
Roadmap for Unconventional Computing with Nanotechnology
G. Finocchio, K. Tatsumura, H. Goto et al.
Nano Futures 8, 012001 (2024)
Control of the ZZ coupling between Kerr cat qubits via transmon couplers
Takaaki Aoki, Taro Kanao, Hayato Goto, Shiro Kawabata, Shumpei Masuda
Physical Review Applied 21, 014030 (2024)
Measurement-free fault-tolerant logical-zero-state encoding of the distance-three nine-qubit surface code in a one-dimensional qubit array
Hayato Goto, Yinghao Ho, Taro Kanao
Physical Review Research 5, 043137 (2023)
Fast parametric two-qubit gate for highly detuned fixed-frequency superconducting qubits using a double-transmon coupler
Kentaro Kubo, Hayato Goto
Applied Physics Letters 122, 064001 (2023)
Correlation-diversified portfolio construction by finding maximum independent set in large-scale market graph
R. Hidaka, Y. Hamakawa, J. Nakayama, K. Tatsumura
IEEE Access 11, 142979-142991 (2023)
Pairs-trading System using Quantum-inspired Combinatorial Optimization Accelerator for Optimal Path Search in Market Graphs
K. Tatsumura, R. Hidaka, J. Nakayama, T. Kashimata, M. Yamasaki
IEEE Access 11, 104406-104416 (2023)
Real-time Trading System based on Selections of Potentially Profitable, Uncorrelated, and Balanced Stocks by NP-hard Combinatorial Optimization
K. Tatsumura, R. Hidaka, J. Nakayama, T. Kashimata, M. Yamasaki
IEEE Access 11, 120023-120033 (2023)
Simulated bifurcation for higher-order cost functions
Taro Kanao, Hayato Goto
Applied Physics Express 16, 014501 (2023)
Two-qubit gate using conditional driving for highly detuned Kerr nonlinear parametric oscillators
Hiroomi Chono, Taro Kanao, Hayato Goto
Physical Review Research 4, 043054 (2022)
Distance-based clustering using QUBO formulations
Nasa Matsumoto, Yohei Hamakawa, Kosuke Tatsumura, Kazue Kudo
Scientific Reports 12, 2669 (2022)
Fast Tunable Coupling Scheme of Kerr Parametric Oscillators Based on Shortcuts to Adiabaticity
S. Masuda, T. Kanao, H. Goto, Y. Matsuzaki, T. Ishikawa, S. Kawabata
Physical Review Applied 18, 034076 (2022)
Double-Transmon Coupler: Fast Two-Qubit Gate with No Residual Coupling for Highly Detuned Superconducting Qubits
Hayato Goto
Physical Review Applied 18, 034038 (2022)
Gaussian-wave-packet model for single-photon generation based on cavity quantum electrodynamics under adiabatic and nonadiabatic conditions
Takeru Utsugi, Akihisa Goban, Yuuki Tokunaga, Hayato Goto, Takao Aoki
Physical Review A 106, 023712 (2022)
Quantum Gate for a Kerr Nonlinear Parametric Oscillator Using Effective Excited States
Taro Kanao, Shumpei Masuda, Shiro Kawabata, Hayato Goto
Physical Review Applied 18, 014019 (2022)
Simulated bifurcation assisted by thermal fluctuation
Taro Kanao, Hayato Goto
Communications Physics 5, 153 (2022)
Spectroscopic observation of the crossover from a classical Duffing oscillator to a Kerr parametric oscillator
T. Yamaji, S. Kagami, A. Yamaguchi, T. Satoh, K. Koshino, H. Goto, Z. R. Lin, Y. Nakamura, T. Yamamoto
Physical Review A 105, 023519 (2022)
2021
Chaos in coupled Kerr-nonlinear parametric oscillators
Hayato Goto, Taro Kanao
Physical Review Research 3, 043196 (2021)
Requirements for fault-tolerant quantum computation with cavity-QED-based atom-atom gates mediated by a photon with a finite pulse length
Rui Asaoka, Yuuki Tokunaga, Rina Kanamoto, Hayato Goto, Takao Aoki
Physical Review A 104, 043702 (2021)
Scaling out Ising machines using a multi-chip architecture for simulated bifurcation
K. Tatsumura, M. Yamasaki, H. Goto
Nature Electronics 4, 208-217 (2021)
High-performance combinatorial optimization based on classical mechanics
Hayato Goto, Kotaro Endo, Masaru Suzuki, Yoshisato Sakai, Taro Kanao, Yohei Hamakawa, Ryo Hidaka, Masaya Yamasaki, Kosuke Tatsumura
Science Advances 7, eabe7953 (2021)
High-accuracy Ising machine using Kerr-nonlinear parametric oscillators with local four-body interactions
Taro Kanao, Hayato Goto
npj Quantum Information 7, 18 (2021)
2020
A Currency Arbitrage Machine based on the Simulated Bifurcation Algorithm for Ultrafast Detection of Optimal Opportunity
Kosuke Tatsumura, Ryo Hidaka, Masaya Yamasaki, Yoshisato Sakai, Hayato Goto
IEEE Int. Symp. Circuits and Syst. (ISCAS), pp. 1-5 (2020)
Quantum annealing using vacuum states as effective excited states of driven systems
Hayato Goto, Taro Kanao
Communications Physics 3, 235 (2020)
2019
FPGA-based Simulated Bifurcation Machine
Kosuke Tatsumura, Alexander R. Dixon, Hayato Goto
Proc. of IEEE Int'l Conf. on Field-Programmable Logic and Applications (FPL), 59-66 (2019)
Figure of merit for single-photon generation based on cavity quantum electrodynamics
Hayato Goto, Shota Mizukami, Yuuki Tokunaga, Takao Aoki
Physical Review A 99, 053843 (2019)
Combinatorial optimization by simulating adiabatic bifurcations in nonlinear Hamiltonian systems
Hayato Goto, Kosuke Tatsumura, Alexander R. Dixon
Science Advances 5, eaav2372 (2019)
Quantum Computation Based on Quantum Adiabatic Bifurcations of Kerr-Nonlinear Parametric Oscillators
Hayato Goto
Journal of the Physical Society of Japan 88, 061015 (2019)
On-demand generation of traveling cat states using a parametric oscillator
Hayato Goto, Zhirong Lin, Tsuyoshi Yamamoto, Yasunobu Nakamura
Physical Review A 99 023838, (2019)
2018
Boltzmann sampling from the Ising model using quantum heating of coupled nonlinear oscillators
Hayato Goto, Zhirong Lin, Yasunobu Nakamura
Scientific Reports 8, 7154 (2018)
2017
Large-scale Ising-machines composed of magnetic neurons
Koichi Mizushima, Hayato Goto, Rie Sato
Applied Physics Letters 111, 172406 (2017)
Work sharing of qubits in topological error corrections
Tetsufumi Tanamoto, Hayato Goto
Physical Review A 96, 022324 (2017)
2016
Suppressing gate errors in frequency-domain quantum computation through extra physical systems coupled to a cavity
Satoshi Nakamura, Hayato Goto, Mamiko Kujiraoka, Kouichi Ichimura
Physical Review A 94, 062306 (2016)
Universal quantum computation with a nonlinear oscillator network
Hayato Goto
Physical Review A 93, 050301(R) (2016)
Bifurcation-based adiabatic quantum computation with a nonlinear oscillator network
Hayato Goto
Scientific Reports 6, 21686 (2016)
Minimizing resource overheads for fault-tolerant preparation of encoded states of the Steane code
Hayato Goto
Scientific Reports 6, 19578 (2016)
2015
Frequency-domain quantum computation to selectively manipulate many qubits
Satoshi Nakamura, Hayato Goto, Mamiko Kujiraoka, Kouichi Ichimura
Physical Review A 91, 012309 (2015)
2014
Step-by-step magic state encoding for efficient fault-tolerant quantum computation
Hayato Goto
Scientific Reports 4, 7501 (2014)
Resource requirements for a fault-tolerant quantum Fourier transform
Hayato Goto
Physical Review A 90, 052318 (2014)
Soft-decision decoder for quantum erasure and probabilistic-gate error models
Hayato Goto, Hironori Uchikawa
Physical Review A 89, 022322 (2014)
2013
Cavity-enhanced spectroscopy of a rare-earth-ion-doped crystal: Observation of a power law for inhomogeneous broadening
Hayato Goto, Satoshi Nakamura, Mamiko Kujiraoka, Kouichi Ichimura
Optics Express 21, 24332-24343 (2013)
Fault-tolerant quantum computation with a soft-decision decoder for error correction and detection by teleportation
Hayato Goto, Hironori Uchikawa
Scientific Reports 3, 2044 (2013)
Quantum phase gate via stimulated Raman adiabatic passage with time-dependent two-photon detuning
Satoshi Nakamura, Hayato Goto, Kouichi Ichimura
Optics Communications 293, 160-165 (2013)
2010
Experimental determination of intracavity losses of monolithic Fabry-Perot cavities made of Pr3+:Y2SiO5
Hayato Goto, Satoshi Nakamura, Kouichi Ichimura
Optics Express18, 23763-23775 (2010)
Condition for fault-tolerant quantum computation with a cavity-QED scheme
Hayato Goto, Kouichi Ichimura
Physical Review A 82, 032311 (2010)
2009
Fault-tolerant quantum computation with probabilistic two-qubit gates
Hayato Goto, Kouichi Ichimura
Physical Review A 80, 040303(R) (2009)
2008
Reformulation of the quantum Zeno effect for exponentially decaying systems
Hayato Goto, Kouichi Ichimura
Physical Review A 78, 044102 (2008)
Quantum phase transition in the generalized Dicke model: Inhomogeneous coupling and universality
Hayato Goto, Kouichi Ichimura
Physical Review A 77, 053811 (2008)
Stimulated Raman adiabatic passage with small two-photon detunings and its geometrical description
Hayato Goto, Kouichi Ichimura
Physics Letters A 372, 1535-1540 (2008)
Upper bound for the success probability of cavity-mediated adiabatic transfer in the presence of dissipation
Hayato Goto, Kouichi Ichimura
Physical Review A 77, 013816 (2008)
Nonclassical photon statistics in cavity QED with an inhomogeneous medium
Hayato Goto, Kouichi Ichimura
Physical Review A 77, 015804 (2008)
2007
Geometric phase for mixed states: Formulation based on a connection on a vector bundle over a Grassmann manifold
Hayato Goto, Kouichi Ichimura
Physical Review A 76, 012120 (2007)
Observation of coherent population transfer in a four-level tripod system with a rare-earth-metal-ion-doped crystal
Hayato Goto, Kouichi Ichimura
Physical Review A 75, 033404 (2007)
2006
Normal-mode coupling of rare-earth-metal ions in a crystal to a macroscopic optical cavity mode
Kouichi Ichimura, Hayato Goto
Physical Review A 74, 033818 (2006)
Population transfer via stimulated Raman adiabatic passage in a solid
Hayato Goto, Kouichi Ichimura
Physical Review A 74, 053410 (2006)
2005
Quantum trajectory simulation of controlled phase-flip gates using the vacuum Rabi splitting
Hayato Goto, Kouichi Ichimura
Physical Review A 72, 054301 (2005)
Nonclassical photon statistics of the light from a weakly driven cavity containing weakly driven two-level atoms
Hayato Goto, Kouichi Ichimura
Optics Communications 248, 493-499 (2005)
2004
Multiqubit controlled unitary gate by adiabatic passage with an optical cavity
Hayato Goto, Kouichi Ichimura
Physical Review A 70, 012305 (2004)
2001
A simple frequency-domain quantum computer with ions in a crystal coupled to a cavity mode
Kouichi Ichimura
Optics Communications 196, 119-125 (2001)
1998
Enhanced and reduced absorptions via quantum interference: Solid system driven by a rf field
Kazushige Yamamoto, Kouichi Ichimura, Nobuhiro Gemma
Physical Review A 58, 2460-2466 (1998)
Evidence for electromagnetically induced transparency in a solid medium
K. Ichimura, K. Yamamoto, and N. Gemma
Physical Review A 58, 4116-4120 (1998)
Lectures and Interviews
2024
Simulated Bifurcation Machines: Enabling NP-hard Optimization-based Judgement in Realtime systems by Quantum-inspiredTechnology
K. Tatsumura
IEEE International Workshop on Ising Machines(IISM), 2024.4.16
https://www.petaspin.com/isingmachines2024/
Simulated bifurcation machines: combinatorial optimization accelerators based on a quantum-inspired parallelizable algorithm
K. Tatsumura
Symposium on VLSI Technology and Circuits, 2023.6.
Combinatorial Optimization Machines Using Quantum or Classical Parametric Oscillators
H.Goto
International Conference on Electronics Packaging 2021 2021.05.14
Combinatorial optimization using quantum or classical driven systems
H.Goto
APS March Meeting 2021 2021.03.16
Simulated bifurcation algorithm for large-scale combinatorial optimization
H.Goto
ASP-DAC2021, Designers’ Forum, Session 8A-2 2021.01.21
History
2024
・Published a paper on the successful realization of the Double-Transmon Coupler in collaboration with RIKEN, achieving a 99.90% two-qubit gate fidelity.
2022
・Published a paper on the theoretical proposal of the double-transmon coupler.
2021
・Theoretically discovered the double-transmon coupler.
・Published a paper on second-generation simulated bifurcation algorithms.
2019
・Published the first paper on simulated bifurcation machines.
2017
・Discovered the simulated bifurcation algorithm from the theory of quantum bifurcation machines.
2016
・Published two papers on quantum bifurcation machines (annealing type and gate type).
・Published a paper on a minimal-resource encoding method for the Steane code, a representative quantum error–correcting code.
2015
・Theoretically discovered quantum bifurcation machines by replacing two-photon loss and one- photon loss in coherent Ising machines with the Kerr effect and detuning, respectively.
2013
・Published a paper on optimal decoding of concatenated quantum codes based on probabilistic inference.
2010
・Published a paper on large improvements to the threshold value of fault-tolerant quantum computing with a cavity quantum electrodynamics system.
2006
・Published a paper on the world’s first experimental realization of stimulated Raman adiabatic passage (STIRAP) in solids.
2001
・Published a paper proposing the theory of quantum computers using electromagnetically induced transparency (EIT) in solids.
1998
・Published a paper on the observation of EIT in solids by using crystal doped with rare earth ions (Pr3+: Y2SiO5).
Related Links
Quantum-Inspired Optimization Solutions
Link to Toshiba Digital Solutions Corporation page.
Quantum Key Distribution
Link to Toshiba Digital Solutions Corporation page.