K. Slowik, A. Raczynski, J. Zaremba, S. Zielinska-Kaniasty
An implementation is proposed of single qubit gates, e.g., phase, NOT, \sqrt{NOT} and Hadamard, operating on polarized photons and based on light storage. Instead of processing photons themselves, qubit transformations are performed on atomic excitations due to photon storage in a medium of atoms in the tripod configuration.
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Quantum information stored in a qubit is rapidly lost to the environment. The realization of robust qubits is one of the most important challenges in quantum computing. Herein we propose to embed a logical qubit within the manifold of a qudit as a scheme to preserve quantum information over extended periods of time. Under identical conditions (e.g. decoherence channels) the submanifold of the logical qubit exhibits extended lifetimes compared to a pure two-level system (qubit). The retention of quantum information further improves with separation between the sublevels of the logical qubit. Lif…
Transversal Diagonal Logical Operators for Stabiliser Codes
本研究针对CSS码，提出识别所有横向对角逻辑算子的更通用或更低复杂度算法，并给出构造具有所需对角逻辑克利福德层级算子的CSS码的方法，以推进容错量子计算。
To realize fault-tolerant quantum computing, it is necessary to store quantum information in logical qubits with error correction functions, realized by distributing a logical state among multiple physical qubits or by encoding it in the Hilbert space of a high-dimensional system. Quantum gate operations between these error-correctable logical qubits, which are essential for implementation of any practical quantum computational task, have not been experimentally demonstrated yet. Here we demonstrate a geometric method for realizing controlled-phase gates between two logical qubits encoded in p…
In [Hastings et al 2014] it is stated that the code distance of a logical qubit stored using dislocations is 2L + O(1), where L is the separation between the dislocation twists. This code distance assumed only physical X and Z errors are permitted. This short note shows that, when Y errors are allowed, the code distance reduces to L + O(1). See Figure 1.
Future ground-based quantum information networks will likely use single photons transmitted through optical fibers to entangle individual network nodes. To extend communication distances and overcome limitations due to photon absorption in fibers the concept of quantum repeaters has been proposed. For that purpose, it is required to achieve quantum correlations between the material nodes and photons at telecom wavelengths which can be sent over long distances in optical fibers. Here we demonstrate non-classical correlation between a frequency converted telecom C-band photon and a spin-wave sto…
Universal quantum computation is striking for its unprecedented capability in processing information, but its scalability is challenging in practice because of the inevitable environment noise. Although quantum error correction (QEC) techniques have been developed to protect stored quantum information from leading orders of errors, the noise-resilient processing of the QEC-protected quantum information is highly demanded but remains elusive. Here, we demonstrate phase gate operations on a logical qubit encoded in a bosonic oscillator in an error-transparent (ET) manner. Inspired by Refs. [9,10…
Logical gates on Floquet codes via folds and twists
本文通过折叠和扭转技术在Floquet码上实现逻辑门，展示了其在纠错码中的应用和性能优势。
Fast logical operations in quantum LDPC codes using simple resource states
研究如何在量子LDPC码中快速进行逻辑运算，提出仅用猫态的方法，设计联合测量协议及调度器码，经数值模拟，该方法在测量可交换逻辑算子、随机克利福德电路及非克利福德门时均有显著加速。
Long-time storage of a decoherence-free subspace logical qubit in a dual-type quantum memory
本文在低温离子阱中实现双型多离子量子存储器，将无退相干子空间逻辑量子比特的相干时间提升至两小时以上，并展示了更好的可扩展性。
To date, a great deal of attention has focused on characterizing the performance of quantum error correcting codes via their thresholds, the maximum correctable physical error rate for a given noise model and decoding strategy. Practical quantum computers will necessarily operate below these thresholds meaning that other performance indicators become important. In this work we consider the scaling of the logical error rate of the toric code and demonstrate how, in turn, this may be used to calculate a key performance indicator. We use a perfect matching decoding algorithm to find the scaling o…
Logical quantum processor based on reconfigurable atom arrays
该研究在可重构中性原子阵列上实现可编程逻辑量子处理器，利用逻辑级控制、分区架构和多种量子纠错编码，展示容错逻辑门、GHZ态、前馈隐形传态及48逻辑量子比特复杂采样。
The ability to protect quantum information from the effect of noise is one of the major goals of quantum information processing. In this article, we study limitations on the asymptotic stability of quantum information stored in passive N-qubit systems. We consider the effect of small imperfections in the implementation of the protecting Hamiltonian in the form of perturbations or weak coupling to a ground state environment. We prove that, regardless of the protecting Hamiltonian, there exists a perturbed evolution that necessitates a final error correcting step when the state of the memory is …
In this paper I explore the entanglement evolution of qubits that are part of a five qubit quantum error correction code subject to various decohering environments. Specifically, I look for possible parallels between the entanglement degradation and the fidelity of the logical qubit of quantum information stored in the physical qubits. In addition, I note the possible exhibition of entanglement sudden death (ESD) due to decoherence and question whether ESD is actually a roadblock to successful quantum computation.
Enhancing the Yield of Bucket Brigade Quantum Random Access Memory using Redundancy Repair
本文提出一种利用冗余量子比特提升qRAM产量的新型内存架构，通过减少制造误差带来的影响，显著提高量子计算系统的性能。
Practical gates by Majorana fermion motion
本文通过马约拉纳费米子运动实现容错逻辑门，提出紧凑运动原语以降低空间开销，数值表明在近期错误率下优于晶格手术。
Mixed-state phase structure of gauge-Higgs subsystem codes under logical-preserving decoherence
本研究从子系统码视角探究局域规范对称退相干对规范-希格斯模型（GHM）的影响，阐明其全局相图，发现退相干诱导的非常规临界混合态，分析其逻辑空间鲁棒性并通过映射至环面码理解性质。
Quantum error correction protects fragile quantum information by encoding it into a larger quantum system. These extra degrees of freedom enable the detection and correction of errors, but also increase the operational complexity of the encoded logical qubit. Fault-tolerant circuits contain the spread of errors while operating the logical qubit, and are essential for realizing error suppression in practice. While fault-tolerant design works in principle, it has not previously been demonstrated in an error-corrected physical system with native noise characteristics. In this work, we experimenta…
Ultimate bounds on the maximum operating frequency of networks of quantum dot cellular automata devices have yet to be established. We consider the adiabaticity of such networks in the two-state approximation where clocking is achieved via modulation of the inter-dot tunneling barriers. Estimates of the maximum operating frequency that would allow a 99% probability of observing the correct logical output are presented for a subset of the basic components used in QCA network design. Simulations are performed both in the coherent limit and for a simple dissipative model. We approach the problem …
Syndrome resampling enhances quantum error correction thresholds
本文提出通过重新采样症候提高量子纠错阈值，通过优化解码器和减少逻辑错误率，提升近似量子纠错实验的保真度。
Photonics is a promising architecture for the realisation of quantum information processing, since the two-photon interaction, or non-linearity, necessary to build logical gates can efficiently be realised by the use of interference with ancillary photons and detection. Although single-photon sources and detectors are pivotal in realisations of such systems, clear guidelines for the required performance of realistic systems are yet to be defined. We present our detailed numerical simulation of several quantum optics circuits including sources and detectors all represented in multi-dimensional …
We propose an efficient method for mapping and storage of a quantum state of propagating light in atoms. The quantum state of the light pulse is stored in two sublevels of the ground state of a macroscopic atomic ensemble by activating a synchronized Raman coupling between the light and atoms. We discuss applications of the proposal in quantum information processing and in atomic clocks operating beyond quantum limits of accuracy. The possibility of transferring the atomic state back on light via teleportation is also discussed.
Quantum resource estimates for computing binary elliptic curve discrete logarithms
本文用窗口化 Shor 电路精确实现二元椭圆曲线点加法，估算逻辑/物理资源，证明光子 active-volume 架构可显著缩短运行时间。
Cat states of the microwave field stored in high-Q resonators show great promise for robust encoding and manipulation of quantum information. Here we propose an approach to efficiently prepare such cat states in a Kerr-nonlinear resonator by the use of a two-photon drive. We show that this preparation is robust against single-photon loss. We moreover find that it is possible to remove undesirable phase evolution induced by a Kerr nonlinearity using a two-photon drive of appropriate amplitude and phase. Finally, we present a universal set of quantum logical gates that can be performed on the en…
Distributed quantum error correction based on hyperbolic Floquet codes
本文提出利用双曲傅科码实现分布式量子纠错，通过高效存储逻辑量子比特和简化测量过程，实现了高保真度的纠错性能。
Quantum memories are key components in quantum information networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their long storage times and experimental simplicity. Operation with the Raman protocol enables high time-bandwidth products, which allows for multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing. This makes the Raman memory a promising tool, whose broad spe…
Large-scale quantum information processors must be able to transport and maintain quantum information, and repeatedly perform logical operations. Here we demonstrate a combination of all the fundamental elements required to perform scalable quantum computing using qubits stored in the internal states of trapped atomic ions. We quantify the repeatability of a multi-qubit operation, observing no loss of performance despite qubit transport over macroscopic distances. Key to these results is the use of different pairs of beryllium ion hyperfine states for robust qubit storage, readout and gates, a…
We introduce a new class of primitive building blocks for realizing quantum logic elements based on nanoscale magnetization textures called skyrmions. In a skyrmion qubit, information is stored in the quantum degree of helicity, and the logical states can be adjusted by electric and magnetic fields, offering a rich operation regime with high anharmonicity. By exploring a large parameter space, we propose two skyrmion qubit variants depending on their quantized state. We discuss appropriate microwave pulses required to generate single-qubit gates for quantum computing, and skyrmion multiqubit s…
Accessible Quantum Gates on Classical Stabilizer Codes
针对强噪声偏置物理量子比特的纠错需求，研究经典稳定子码上的量子门实现，证明通用逻辑门集需复杂幺正电路，推动偏置噪声稳定子码框架内替代逻辑门构造的研究。
We study spatial multimode quantum memories based on light storage in extended ensembles of Lambda-type atoms. We show that such quantum light-matter interfaces allow for highly efficient storage of many spatial modes. In particular, forward operating memories possess excellent scaling with the important physical parameters: quadratic scaling with the Fresnel number and even cubic with the optical depth of the atomic ensemble. Thus, the simultaneous use of both the longitudinal and transverse shape of the stored spin wave modes constitutes a valuable and so far overlooked resource for multimod…
Erasure-tolerance scheme for the surface codes on neutral atom quantum computers
针对中性原子量子计算机中擦除误差持续累积的问题，本文提出k-shift擦除恢复方案，通过码形变反复转移逻辑量子比特并安全纠正原子阵列擦除，为实用容错提供可行路径。
Although the initial proposal for ion trap quantum computation made use of an auxiliary internal level to perform logic between ions, this resource is not necessary in principle. Instead, one may perform such operations directly using sideband laser pulses, operating with an arbitrary (sufficiently small) Lamb-Dicke parameter. We explore the potential of this technique, showing how to perform logical operations between the internal state of an ion and the collective motional state and giving explicit constructions for a controlled-not gate between ions.
Topological quantum memories in two dimensions are not thermally stable, since once a quasiparticle excitation is created, it will delocalise at no energy cost. This places an upper bound on the lifetime of quantum information stored in them. We address this issue for a topological subsystem code introduced in [Bravyi S. et al., Quant.Inf.Comp.13(11):0963]. By frequently measuring the gauge operators of the code, a technique known as Operator Quantum Zeno Effect [Li Y. et al, preprint arXiv:1305.2464], the dynamics responsible for quasiparticle motion is suppressed, and can eventually be "froz…
Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits encoded in high-dimensional systems. Typically, logical qubits are encoded in multiple two-level systems, but entangling gates operating on such qubits are highly complex and have not yet been demonstrated. Here, we realize a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities. In this approach, we encode a qubit in the high-dimensional space of a single cavity mode, rathe…
The classical methods used by recursion theory and formal logic to block paradoxes do not work in quantum information theory. Since quantum information can exist as a coherent superposition of the classical ``yes'' and ``no'' states, certain tasks which are not conceivable in the classical setting can be performed in the quantum setting. Classical logical inconsistencies do not arise, since there exist fixed point states of the diagonalization operator. In particular, closed timelike curves need not be eliminated in the quantum setting, since they would not lead to any paradoxical outcome cont…
All-optical quantum memory using bosonic quantum error correction codes
本文提出全光学量子记忆架构，利用玻色量子纠错码在光纤环中存储量子比特，并通过周期性 teleportation 纠错提升稳定性。优化解码策略显著提升逻辑性能，确定最佳压缩与校正频率权衡，为光子量子记忆提供设计原则。
A Review of Software for Designing and Operating Quantum Networks
本文综述了量子网络设计与操作软件的现状，指出理论协议与实际实现之间的差距，并提出开发可扩展软件架构以支持混合大规模量子网络的路线图。
Adaptive Control of Stochastic Error Accumulation in Fault-Tolerant Quantum Computation
本文提出通过自适应控制策略解决量子容错中随机误差累积问题，采用Ch-DQN算法跟踪噪声演变，抑制危险变量累积，提升逻辑生存时间。
The study of advanced quantum devices for energy storage has attracted the attention of the scientific community in the past few years. Although several theoretical progresses have been achieved recently, experimental proposals of platforms operating as quantum batteries under ambient conditions are still lacking. In this context, this work presents a feasible realization of a quantum battery in a carboxylate-based metal complex, which can store a finite amount of extractable work under the form of quantum discord at room temperature, and recharge by thermalization with a reservoir. Moreover, …
A real-time, scalable, fast and highly resource efficient decoder for a quantum computer
针对量子计算机解码器需高效、高速以支撑大规模量子比特运行的需求，提出Collision Clustering解码器并在FPGA与ASIC上实现，可高速支持超千量子比特表面码解码，功耗极低，为容错量子计算机落地提供可行路径。
Hybrid entanglement and error correction in a scalable quantum network node
本文基于金刚石色心构建混合量子网络节点，实现电子、核与光子量子比特的跨频段纠缠，并利用三量子比特重复码和实时反馈完成多达十二轮主动纠错。
WISER: Systematic Design-Space Exploration of Trapped Ions with Multiplexed Control
WISER提出跨层设计空间探索框架，评估WISE全局控制囚禁离子架构的容错可行性，发现其可行空间狭窄，且布线可扩展性与逻辑吞吐量存在根本权衡，需大幅降低物理错误率和电路深度。
Reducing quantum error correction overhead using soft information
本文研究了软信息在不同物理量子比特平台上的解码效果，展示了其在降低编码距离和提高物理错误率时的纠错优势，通过模拟表面码和双变量自行车码的量子记忆，证明软信息能显著提升纠错性能。
The stable operation of quantum computers will rely on error-correction, in which single quantum bits of information are stored redundantly in the Hilbert space of a larger system. Such encoded qubits are commonly based on arrays of many physical qubits, but can also be realized using a single higher-dimensional quantum system, such as a harmonic oscillator. A powerful encoding is formed from a periodically spaced superposition of position eigenstates. Various proposals have been made for realizing approximations to such states, but these have thus far remained out of reach. Here, we demonstra…
Proposals to measure non-Abelian anyons in a superconductor by quantum interference of vortices suffer from the predominantly classical dynamics of the normal core of an Abrikosov vortex. We show how to avoid this obstruction using coreless Josephson vortices, for which the quantum dynamics has been demonstrated experimentally. The interferometer is a flux qubit in a Josephson junction circuit, which can nondestructively read out a topological qubit stored in a pair of anyons --- even though the Josephson vortices themselves are not anyons. The flux qubit does not couple to intra-vortex excita…
We report the observation of subradiance in dense ensembles of cold $^{87}$Rb atoms operating near Dicke's regime of a large number of atoms in a volume with dimensions smaller than the transition wavelength. We validate that the atom number is the only cooperativity parameter governing subradiance. We probe the dynamics in the many-body regime and support the picture that multiply-excited subradiant states are built as a superposition of singly-excited states that decay independently. Moreover, we implement an experimental procedure to release the excitation stored in the long-lived modes in …
This work reports the functioning of a single atom energy-conversion device, operating either as a quantum engine or a refrigerator, coupled to a quantum load. The "working fluid" is comprised of two optical levels of a single ion, and the load is one vibrational mode of the same ion cooled down to the quantum regime. The energy scales of these two modes differ by 9 orders of magnitude. We realize cyclic energy transfers between the working fluid and the quantum load, either increasing or decreasing the population of the vibrational mode. This is achieved albeit the interaction between the loa…
Architectural mechanisms of a universal fault-tolerant quantum computer
本研究通过中性原子阵列实现了通用容错量子计算架构，展示了量子纠错、逻辑纠缠与量子态传输的结合，为大规模量子计算提供了基础。
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