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Limitations to Dynamical Error Suppression and Gate-Error Virtualization from Temporally Correlated Nonclassical Noise

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PRX quantum 2025年第1期6卷 010323-010323页

作者： Michiel Burgelman Nattaphong Wonglakhon Diego N. Bernal-García Gerardo A. Paz-Silva Lorenza Viola Department of Physics and Astronomy Dartmouth College Hanover New Hampshire 03755 USA Centre for Quantum Computation and Communication Technology (Australian Research Council) Centre for Quantum Dynamics Griffith University Brisbane Queensland 4111 Australia

Realistic multiqubit noise processes often result in error mechanisms that are not captured by the probabilistic Markovian error models commonly employed in circuit-level analyses of quantum fault tolerance. By working within an open-quantum system Hamiltonian formulation, we revisit the validity of the notion of a constant gate error in the presence of noise that is both temporally correlated and nonclassical, and the impact of which is mitigated through perfect instantaneous dynamical decoupling subject to finite timing constraints. We study a minimal exactly solvable single-qubit model under Gaussian quantum dephasing noise, showing that the fidelity of a dynamically protected idling gate can depend strongly on its location in the circuit and the history of applied control, even when the system-side error propagation is fully removed through perfect reset operations. For digital periodic control, we prove that, under mild conditions on the low-frequency behavior of the nonclassical noise spectrum, the gate fidelity saturates at a value that is strictly smaller than the one attainable in the absence of control history; the presence of high-frequency noise peaks is also found as especially harmful, due to the possible onset of control-induced resonances. We explicitly relate these features to the evolution of the bath statistics during the computation, which has not been fully accounted for in existing treatments. We find that only if decoupling can keep the qubit highly pure over a time scale larger than the correlation time of the noise, the bath approximately converges to its original statistics and a stable-in-time control performance is recovered. Our work highlights the significance of the full bath evolution between circuit locations and suggests that additional trade-offs and design constraints may arise in layered quantum fault-tolerant architectures from the need to appropriately reequilibrate the quantum bath statistics, particularly when Markovian noise

关键词： Hamiltonians

Resource overheads and attainable rates for trapped-ion lattice surgery

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Physical Review Research 2025年第2期7卷 023088-023088页

作者： Hudson Leone Thinh Le S. Srikara Simon Devitt Centre for Quantum Software and Information University of Technology Sydney Sydney 2007 Australia Centre for quantum computation and Communication Technology (CQC2T) InstituteQ Aalto University 02150 Espoo Finland

We present estimates for the number of ions needed to implement fault-tolerant lattice surgery between spatially separated trapped-ion surface codes. Additionally, we determine attainable lattice surgery rates given a number of dedicated “communication ions” per logical qubit. Because our analysis depends heavily on the rate that syndrome extraction cycles take place, we survey the state-of the art and propose three possible cycle times between 10 and 1000µs that we could reasonably see realized provided certain technological milestones are met. Consequently, our numerical results indicate that hundreds of resource ions will be needed for lattice surgery in the slowest case, while close to a hundred thousand will be needed in the fastest case. The main factor contributing to these prohibitive estimates is the limited rate that ions can be coupled across traps. Our results indicate an urgent need for optical coupling to improve by one or more orders of magnitude for trapped-ion quantum computers to scale.

关键词： Qubits

Instantaneous quantum Polynomial-Time Sampling and Verifiable quantum Advantage: Stabilizer Scheme and Classical Security

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PRX quantum 2025年第2期6卷 020315-020315页

作者： Michael J. Bremner Bin Cheng Zhengfeng Ji Centre for Quantum Software and Information University of Technology Sydney Sydney New South Wales 2007 Australia Centre for Quantum Computation and Communication Technology New South Wales 2052 Australia Centre for Quantum Technologies National University of Singapore Singapore Department of Computer Science and Technology Tsinghua University Beijing China Zhongguancun Laboratory

Sampling problems demonstrating beyond classical computing power with noisy intermediate-scale quantum devices have been experimentally realized. In those realizations, however, our trust that the quantum devices faithfully solve the claimed sampling problems is usually limited to simulations of smaller-scale instances and is, therefore, indirect. The problem of verifiable quantum advantage aims to resolve this critical issue and provides us with greater confidence in a claimed advantage. Instantaneous quantum polynomial-time (IQP) sampling has been proposed to achieve beyond classical capabilities with a verifiable scheme based on quadratic-residue codes (QRC). Unfortunately, this verification scheme was recently broken by an attack proposed by Kahanamoku-Meyer. In this work, we revive IQP-based verifiable quantum advantage by making two major contributions. Firstly, we introduce a family of IQP sampling protocols called the stabilizer scheme, which builds on results linking IQP circuits, the stabilizer formalism, coding theory, and an efficient characterization of IQP-circuit correlation functions. This construction extends the scope of existing IQP-based schemes while maintaining their simplicity and verifiability. Secondly, we introduce the hidden structured code (HSC) problem as a well-defined mathematical challenge that underlies the stabilizer scheme. To assess classical security, we explore a class of attacks based on secret extraction, including Kahanamoku-Meyer’s attack as a special case. We provide evidence of the security of the stabilizer scheme, assuming the hardness of the HSC problem. We also point out that the vulnerability observed in the original QRC scheme is primarily attributed to inappropriate parameter choices, which can be naturally rectified with proper parameter settings.

关键词： Polynomial approximation

Nonlinear Domain Engineering for quantum Technologies

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arXiv 2025年

作者： Weiss, Tim F. Peruzzo, Alberto Quantum Photonics Laboratory Centre for Quantum Computation and Communication Technology RMIT University MelbourneVIC3000 Australia Qubit Pharmaceuticals Advanced Research Department Paris France

The continuously growing effort towards developing real-world quantum technological applications has come to demand an increasing amount of flexibility from its respective platforms. This review presents a highly adaptable engineering technique for photonic quantum technologies based on the artificial structuring of the material nonlinearity. This technique, while, in a simple form, already featured across the full breadth of photonic quantum technologies, has undergone significant development over the last decade, now featuring advanced, aperiodic designs. This review gives an introduction to the three-wave-mixing processes lying at the core of this approach, and illustrates, on basis of the underlying quantum-mechanical description, how they can artificially be manipulated to engineer the corresponding photon characteristics. It then describes how this technique can be employed to realize a number of very different objectives which are expected to find application across the full range of photonic quantum technologies, and presents a summary of the research done towards these ends to date. © 2025, CC BY.

关键词： quantum optics

Programmable photonic waveguide arrays: opportunities and challenges

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arXiv 2025年

作者： Yang, Yang Youssry, Akram Peruzzo, Alberto Quantum Photonics Laboratory Centre for Quantum Computation and Communication Technology RMIT University MelbourneVIC3000 Australia Qubit Pharmaceuticals Advanced Research Department Paris France

The field of programmable photonics has advanced significantly in recent decades, driven by the rising demand for complex applications, such as optical quantum computing and photonic neural networks. However, as the complexity of these applications increases, there is an increasing need for novel designs that enhance circuit transmission and enable further miniaturization. Photonic waveguide arrays (WAs) hold a unique position in integrated photonics, as they implement "always-on" Hamiltonians and have no direct analogs in free-space optics. They find applications in various fields, including light propagation studies, quantum walks, and topological photonics. Despite their versatility, the lack of reconfigurability has limited their utility and hindered further advancements for a long time. Recently, programmable waveguide arrays (PWAs) have emerged as a promising solution for overcoming the limitations of static WAs and PWA-based architectures have been proven to be universal. This perspective proposes a vision for photonic circuits based on PWAs as a new, interdisciplinary field. We review the history of the development of PWAs and outline their potential in areas such as simulation, communication, sensing, and classical and quantum information processing. This technology is expected to become increasingly feasible with advancements in programmable photonics, nanofabrication, and quantum control. © 2025, CC BY-NC-ND.

关键词： Space optics

Nuclear Spins in a Solid Exceeding 10-Hour Coherence Times for Ultra-Long-Term quantum Storage

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PRX quantum 2025年第1期6卷 010302-010302页

作者： Fudong Wang Miaomiao Ren Weiye Sun Mucheng Guo Matthew J. Sellars Rose L. Ahlefeldt John G. Bartholomew Juan Yao Shuping Liu Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China International Quantum Academy and Shenzhen Branch Hefei National Laboratory Shenzhen 518048 China Centre of Excellence for Quantum Computation and Communication Technology Research School of Physics Australian National University Canberra Australian Capital Territory 0200 Australia Centre for Engineered Quantum Systems School of Physics The University of Sydney Sydney New South Wales 2006 Australia The University of Sydney Nano Institute The University of Sydney Sydney New South Wales 2006 Australia

Long-term quantum storage for quantum communication applications will require optically accessible states with coherence times exceeding the desired storage time. Ground-state hyperfine levels in Eu3+:Y2SiO5 have previously shown coherence times as long as 6 h at 1.4 K when operated at a zero-first-order-Zeeman (ZEFOZ) point. Here, we have characterized the limiting decoherence mechanisms acting in this regime, which shows that the coherence time is limited by the presence of spin impurities. This dephasing effect has been suppressed by cooling the sample to 125 mK, resulting in an extension in the coherence time to over 13 h. In the absence of these impurities, the dominant source of dephasing is the field inhomogeneity of the ZEFOZ point arising from the spin inhomogeneous broadening. We have shown that coherence times over 18 h can be achieved by operating using a spectrally narrow subensemble selected from within the inhomogeneous line. The observed coherence time is longer than that of any other system suitable for an optical quantum memory. Furthermore, at a much higher temperature of 6 K, we have realized a 6-h coherence time, which has been obtainable using single-stage cryocoolers. These results imply advanced engineering feasibility in designing and operating future quantum information-storage devices for a wide range of applications, including in satellites.

关键词： Optical recording

Entanglement distillation rates exceeding the direct transmission bound

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arXiv 2025年

作者： Ghafari, Farzad Dias, Josephine Shalm, L. Krister Verma, Varun B. Slussarenko, Sergei Ralph, Timothy C. Pryde, Geoff J. Centre for Quantum Dynamics Griffith University Yuggera Country BrisbaneQLD4111 Australia Centre for Quantum Computation and Communication Technology Australian Research Council Australia School of Mathematics and Physics University of Queensland Brisbane4072 Australia National Institute of Standards and Technology 325 Broadway BoulderCO80305 United States

Entanglement distribution is crucial for quantum communication and cryptography [1–4] but is hindered by channel loss and decoherence. Noiseless linear amplification (NLA) [5, 6] is a probabilistic protocol that supports noiseless amplification without violating the no-cloning theorem, aiding in tasks like entanglement distillation and enhanced metrology. The probabilistic nature of NLA and other quantum repeater elements creates a significant resource overhead, which depends on the success rate of each individual probabilistic step [1]. We experimentally demonstrate a technique to increase NLA success probability while maintaining the amplification gain and the fidelity of the amplified state with a maximally entangled state. We show that symmetrically distributing loss before and after the amplification provides an improved scaling of the success rates of NLA. Our results are a critical step towards scalable quantum repeaters and enable efficient long-distance quantum communication. © 2025, CC BY.

关键词： quantum entanglement

A Two-Stage Solution to quantum Process Tomography: Error Analysis and Optimal Design

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IEEE Transactions on Information Theory 2025年第3期71卷 1803-1823页

作者： Xiao, Shuixin Wang, Yuanlong Zhang, Jun Dong, Daoyi Mooney, Gary J. Petersen, Ian R. Yonezawa, Hidehiro University of New South Wales School of Engineering and Technology CanberraACT2600 Australia University of Michigan-Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong University Shanghai200240 China The Australian National University School of Engineering CanberraACT2601 Australia Chinese Academy of Sciences Key Laboratory of Systems and Control Academy of Mathematics and Systems Science Beijing100190 China The Australian National University CIICADA Laboratory School of Engineering CanberraACT2601 Australia The University of Melbourne School of Physics ParkvilleVIC3010 Australia RIKEN Center for Quantum Computing Saitama351-0198 Japan Centre for Quantum Computation and Communication Technology Australian Research Council CanberraACT2600 Australia

quantum process tomography is a critical task for characterizing the dynamics of quantum systems and achieving precise quantum control. In this paper, we propose a two-stage solution for both trace-preserving and non-trace-preserving quantum process tomography. Utilizing a tensor structure, our algorithm exhibits a computational complexity of O(MLd2) where d is the dimension of the quantum system and M, L(M≥ d2, L≥ d2) represent the numbers of different input states and measurement operators, respectively. We establish an analytical error upper bound and then design the optimal input states and the optimal measurement operators, which are both based on minimizing the error upper bound and maximizing the robustness characterized by the condition number. Numerical examples and testing on IBM quantum devices are presented to demonstrate the performance and efficiency of our algorithm. © 1963-2012 IEEE.

关键词： Error analysis

General relativistic particle trajectories via quantum mechanical weak values and the Schwarzschild-Alcubierre spacetime

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arXiv 2025年

作者： Foo, Joshua Bellamy, Cameron Ralph, Timothy C. Department of Physics Stevens Institute of Technology Castle Point Terrace HobokenNJ07030 United States Centre for Quantum Computation & Communication Technology School of Mathematics & Physics The University of Queensland St. LuciaQLD4072 Australia

We show that the average trajectories of relativistic quantum particles in Schwarzschild spacetime, obtained via quantum mechanical weak measurements of momentum and energy, are equivalent to the predicted flow lines of probability current in curved spacetime quantum theory. We subsequently demonstrate that these trajectories correspond exactly to classical null geodesics in a hybrid Schwarzschild-Alcubierre spacetime. This threefold equivalence demonstrates how quantum theory in curved spacetime can be formulated via operationally-defined measurements, and that such a theory may be interpreted deterministically, in the spirit of hidden-variable models such as Bohmian mechanics, through the novel connection to an underlying "guiding metric." © 2025, CC BY.

关键词： quantum theory