Linear optical setups for active and passive quantum error correction in polarization encoded qubits
Jose Claudio do Nascimento, Fabio Alencar Mendonca, Rubens Viana Ramos
在这项工作中，我们提出了主动和被动的线性光学设置的量子通信系统中，采用单光子和介观相干态的偏振误差校正。描述了量子通信系统中的应用。
In this work, we present active and passive linear optical setups for error correction in quantum communication systems that employ polarization of single-photon and mesoscopic coherent states. Applications in quantum communication systems are described.
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A Passive and Self-Characterizing Cross-Encoded Receiver for Reference-Frame-Independent Quantum Key Distribution
本文提出一种时间仓编码RFI-QKD全无源接收器，利用时间仓—偏振转换与量子探测器自表征获取实际POVM，并通过原理验证实验证实其可行性与安全性提升。
In this Letter, we propose a new approach to process high-dimensional quantum information encoded in a photon frequency domain. In contrast to previous approaches based on nonlinear optical processes, no active control of photon energy is required. Arbitrary unitary transformation and projection measurement can be realized with passive photonic circuits and time-resolving detection. A systematic circuit design for a quantum frequency comb with arbitrary size has been given. The criteria to verify quantum frequency correlation has been derived. By considering the practical condition of detector…
Security of quantum key distribution with passive basis choice and detection-efficiency mismatch for a realistic satellite setup
本文针对真实卫星QKD场景中探测效率失配显著的问题，提出适配诱骗态方法的被动基选择BB84协议秘密密钥率精确估计方法，为墨子号卫星与兹韦尼哥罗德地面站间QKD实验提供密钥率估计。
Signal state preparation in quantum key distribution schemes can be realized using either an active or a passive source. Passive sources might be valuable in some scenarios; for instance, in those experimental setups operating at high transmission rates, since no externally driven element is required. Typical passive transmitters involve parametric down-conversion. More recently, it has been shown that phase-randomized coherent pulses also allow passive generation of decoy states and Bennett-Brassard 1984 (BB84) polarization signals, though the combination of both setups in a single passive so…
Passive polarization and phase stabilization scheme for Twin-Field QKD
本文提出一种结合类Sagnac干涉仪与即插即用配置的无源方案，同时稳定双场QKD中的相位和偏振，实验实现72小时95.3%的干涉可见度，并支持多用户网络扩展。
Phase error estimation for passive detection setups with imperfections and memory effects
该研究提出了一种通用框架，用于分析具有缺陷和记忆效应的被动探测设置中量子密钥分配协议的相位误差率，以提高安全密钥生成率。
It is well known that an unambiguous discrimination of the four optically encoded Bell states is possible with a probability of $50\%$ at best, when using static, passive linear optics and arbitrarily many vacuum mode ancillae. By adding unentangled single-photon ancillae, we are able to surpass this limit and reach a success probability of at least $75\%$. We discuss the error robustness of the proposed scheme and a generalization to reach a success probability arbitrarily close to $100\%$.
Passive polarization-encoded BB84 protocol using a heralded single-photon source
本文实现了使用 heralded 单光子源的被动偏振编码 BB84 协议，通过被动随机编码简化设计并增强抗侧信道攻击能力，无需诱骗态，优化资源权衡，实现7%量子比特错误率和5kbps安全密钥率，为可扩展量子通信提供实用框架。
We propose a deterministic yet fully passive scheme to transfer the quantum state from a frequency-encoded photon to the spin of a quantum-dot mediated by a nanophotonic waveguide. We assess the quality of the state transfer by studying the effects of all relevant experimental imperfections on the state-transfer fidelity. We show that a transfer fidelity exceeding 95% is achievable for experimentally realistic parameters. Our work sets the stage for deterministic solid-state quantum networks tailored to frequency-encoded photonic qubits.
Measurement-device-independent quantum key distribution (MDI-QKD) with weak coherent sources has been widely and meticulously analyzed. However, the analysis for MDI-QKD with spontaneous parametric-down-conversion sources (SPDCS) is incomplete. In this paper, by accounting for practical parameters of SPDCS with thermal distribution, we presents an investigation on the performances of MDI-QKD under the active three-intensity decoy protocol and the passive one-intensity decoy protocol respectively. Phase randomization, inherently prerequisite for decoy protocol, is taken into consideration for e…
Implementations of quantum and classical gates with linear optical devices and photon number quantum non-demolition measurement for polarization encoded qubits
针对基于光学器件的量子计算机和量子通信系统的构建，本文提出了利用线性光学器件和光子数量子非破坏测量技术实现量子和经典hocTs门的可能方案，以及一种用于产生和分布二体纠缠态的光学装置。
In the Gaussian-modulated coherent state quantum key distribution (QKD) protocol, the sender first generates Gaussian distributed random numbers and then encodes them on weak laser pulses actively by performing amplitude and phase modulations. Recently, an equivalent passive QKD scheme was proposed by exploring the intrinsic field fluctuations of a thermal source [B. Qi, P. G. Evans, and W. P. Grice, Phys. Rev. A 97, 012317 (2018)]. This passive QKD scheme is especially appealing for chip-scale implementation since no active modulations are required. In this paper, we conduct an experimental s…
Proof-of-Principle Demonstration of Fully-Passive Quantum Key Distribution
本研究通过增益开关与后选择技术，在三种信道损耗下实验验证了全被动偏振编码量子密钥分发的可行性，消除了有源调制带来的侧信道风险。
Passive decoy state quantum key distribution: Closing the gap to perfect sources
我们提出了一个量子密钥分发方案，该方案的性能与理想单光子源的性能非常接近。在密钥生成速率和最大可达距离方面，它几乎达到了物理上界。我们的方案依赖于一个实际的设置的基础上的参数下转换源和当今，非理想的光子数检测。包括导致比特错误的任意实验缺陷。我们通过经典的后处理来选择诱饵态。这允许改进有效信号统计和可实现的距离。
Photonic quantum systems are among the most promising architectures for quantum computers. It is well known that for dual-rail photons effective non-linearities and near-deterministic non-trivial two-qubit gates can be achieved via the measurement process and by introducing ancillary photons. While in principle this opens a legitimate path to scalable linear optical quantum computing, the technical requirements are still very challenging and thus other optical encodings are being actively investigated. One of the alternatives is to use single-rail encoded photons, where entangled states can be…
Error suppression in multicomponent cat codes with photon subtraction and teleamplification
本文提出将多光子减除与远程放大结合用于四分量猫码，通过抑制高光子数并配合纠错，在现实损耗条件下实现超过93.5%的最坏情况保真度，为NISQ时代光子量子信息任务中的大无源损耗抑制提供了新方案。
A fully passive transmitter for decoy-state quantum key distribution
本文简化了被动诱骗态QKD发射机原型，采用新方法进行BB84偏振编码和诱骗态生成，并提出严密安全性分析，以消除先前方案中的不必要假设和后选择步骤。
Deterministic quantum teleportation of a path-encoded state using entangled photons
本文提出在线性光学装置中仅用偏振纠缠光子对，通过将任意量子比特态编码到路径自由度实现100%贝尔态测量，从而完成确定性量子隐形传态，平均保真度达88.00%。
Security of passive entanglement-based key distribution protocols
研究基于纠缠的被动密钥分发协议安全性，证明有偏差基选择的被动BBM92及任意方被动QCKA的安全性，数值显示被动BBM92密钥生成率与主动协议相近，为其实际被动实现提供理论基础。
Feasibility study of frequency-encoded photonic qubits over a free-space channel
针对频率仓量子编码此前仅限单模静态信道的问题，本文提出利用视场展宽干涉仪的无源解码方案，并分析相位稳定性要求，验证其在自由空间及星地量子链路中的可行性。
Decoy state method could effectively enhance the performance of quantum key distribution (QKD) with practical phase randomized weak coherent source. Although active modulation of the source intensity is effective and has been implemented in many experiments, passive preparation of decoy states is also an important addition to the family of decoy state QKD protocols. In this paper, following the theory of Curty \emph{et al.} [PRA, 81, 022310 (2010)], we experimentally demonstrate the phase-encoding passive-decoy-state QKD with only linear optical setups and threshold single photon detectors. In…
We study the implementation of quantum key distribution (QKD) systems over quantum repeater infrastructures. We particularly consider quantum repeaters with encoding and compare them with probabilistic quantum repeaters. To that end, we propose two decoder structures for encoded repeaters that not only improve system performance but also make the implementation aspects easier by removing two-qubit gates from the QKD decoder. By developing several scalable numerical and analytical techniques, we then identify the resilience of the setup to various sources of error in gates, measurement modules,…
Fully-Passive Twin-Field Quantum Key Distribution
本文提出一种全被动双场量子密钥分发协议，通过后处理实现基选择、诱骗态准备和编码，消除源调制器和探测器的潜在侧信道，保持高密钥率优势，提升实现安全性和性能。
Most experimental realizations of quantum key distribution are based on the Bennett-Brassard 1984 (so-called BB84) protocol. In a typical optical implementation of this scheme, the sender uses an active source to produce the required BB84 signal states. While active state preparation of BB84 signals is a simple and elegant solution in principle, in practice passive state preparation might be desirable in some scenarios, for instance, in those experimental setups operating at high transmission rates. Passive schemes might also be more robust against side-channel attacks than active sources. Typ…
A robust cryogenic infrastructure in form of a wired, thermally optimized dilution refrigerator is essential for present and future solid-state based quantum processors. Here, we engineer an extensible cryogenic setup, which minimizes passive and active heat loads, while guaranteeing rapid qubit control and readout. We review design criteria for qubit drive lines, flux lines, and output lines used in typical experiments with superconducting circuits and describe each type of line in detail. The passive heat load of stainless steel and NbTi coaxial cables and the active load due to signal dissi…
We present a scheme for implementing homomorphic encryption on coherent states encoded using phase-shift keys. The encryption operations require only rotations in phase space, which commute with computations in the codespace performed via passive linear optics, and with generalized non-linear phase operations that are polynomials of the photon-number operator in the codespace. This encoding scheme can thus be applied to any computation with coherent state inputs, and the computation proceeds via a combination of passive linear optics and generalized non-linear phase operations. An example of s…
Quantum information protocols often rely on tomographic techniques to determine the state of the system. A popular method of encoding information is on the different paths a photon may take, for example, parallel waveguides in integrated optics. However, reconstruction of states encoded onto a large number of paths is often prohibitively resource intensive and requires complicated experimental setups. Addressing this, we present a simple method for determining the state of a photon in a superposition of d paths using a rotating one-dimensional optical Fourier Transform. We establish the theory…
Conditional generation of arbitrary multimode entangled states of light with linear optics
提出了一种在Fock基下概率产生任意多模纠缠态的方案。建议的设置包括被动线性光学，单光子源，强相干激光束，和单光子分辨率的光电探测器。此外，如果量子存储器可用，则该设置的效率可以大大提高。
Linear Optical Quantum Computation with Frequency-Comb Qubits and Passive Devices
本研究提出一种基于时频自由度、用单光子频率梳编码量子比特的无源线性光学量子计算方案，无需有源器件且抗时频误差，现有技术近可满足容错计算要求。
Quantum teleportation is considered a basic primitive in many quantum information processing tasks and has been experimentally confirmed in various photonic and matter-based setups. Here, we consider teleportation of quantum information encoded in modes of a fermionic field. In fermionic systems, superselection rules lead to a more differentiated picture of entanglement and teleportation. In particular, one is forced to distinguish between single-mode entanglement swapping, and qubit teleportation with or without authentication via Bell inequality violation, as we discuss here in detail. We fo…
The correction of errors is of fundamental importance for the development of contemporary computing devices and of robust communication protocols. In this paper we propose a scheme for the implementation of the three-qubit quantum repetition code, exploiting the interaction of Rydberg atoms with the quantized mode of a microwave cavity field. Quantum information is encoded within two circular Rydberg states of the atoms and encoding and decoding process are realized within two separate microwave cavities. We show that errors due to phase noise fluctuations could be efficiently corrected using …
A robust approach for time-bin encoded photonic quantum information protocols
本文提出了一种基于Hong-Ou-Mandel干涉的鲁棒方法，用于生成和测量高维时间槽量子态，克服了传统方法的限制，推动了量子信息科学的发展。
Passive detection of Schwinger boson dynamics via a qubit
本研究提出一种transmon量子比特与微波十字谐振器耦合的集成光子器件，利用量子比特的双重作用实现非接触式高灵敏度的材料时间反演破缺序探测，为研究难接触的关联量子材料提供新途径。
Polarization-encoded photonic quantum-to-quantum Bernoulli factory based on a quantum dot source
本文实验实现了偏振编码光子量子-量子伯努利工厂，通过三种干涉装置实现代数域基本操作并链接成通用工厂，利用高亮度量子点单光子源验证了方案。
We propose a resource-efficient error-rejecting entangled-state analyzer for polarization-encoded multiphoton systems. Our analyzer is based on two single-photon quantum-nondemolition detectors, where each of them is implemented with a four-level emitter (e.g., a quantum dot) coupled to a one-dimensional system (such as a micropillar cavity or a photonic nanocrystal waveguide). The analyzer works in a passive way and can completely distinguish $2^n$ Greenberger-Horne-Zeilinger~(GHZ) states of $n$ photons without using any active operation or fast switching. The efficiency and fidelity of the G…
A Low-Temperature Tunable Microcavity featuring High Passive Stability and Microwave Integration
本研究提出一种闭循环低温光纤基微腔，在低于10K下实现约25皮米的高被动稳定性，并集成微波控制，为自旋-光子界面提供高效平台。
Stabilizer Formalism for Operator Quantum Error Correction
算符量子纠错理论是近年来发展起来的一种新理论，它为主动纠错和被动纠错提供了一个通用的框架。在本文中，我们描述了这些代码的稳定剂形式主义的标准量子纠错理论。这是通过向代码的标准稳定器定义添加“规范”组来实现的，该代码定义了编码状态之间的等价类。规范变换保持编码信息不变;它们的效果被不携带有用信息的虚拟规范量子比特吸收。我们通过识别Shor的9-qubit代码中的规范对称性来说明该结构，该代码允许我们删除其8个稳定器生成器中的4个，从而导致更简单的解码过程和更广泛的逻辑运算类别，而不会影响其基本属性。这为容错量子计算的错误阈值的可能改进开辟了道路。
Decoy states have been proven to be a very useful method for significantly enhancing the performance of quantum key distribution systems with practical light sources. While active modulation of the intensity of the laser pulses is an effective way of preparing decoy states in principle, in practice passive preparation might be desirable in some scenarios. Typical passive schemes involve parametric down-conversion. More recently, it has been shown that phase randomized weak coherent pulses (WCP) can also be used for the same purpose [M. Curty {\it et al.}, Opt. Lett. {\bf 34}, 3238 (2009).] Thi…
An interesting problem in the field of quantum error correction involves finding a physical system that hosts a ``passively protected quantum memory,'' defined as an encoded qubit coupled to an environment that naturally wants to correct errors. To date, a quantum memory stable against finite-temperature effects is only known in four spatial dimensions or higher. Here, we take a different approach to realize a stable quantum memory by relying on a driven-dissipative environment. We propose a new model, the photonic-Ising model, which appears to passively correct against both bit-flip and phase…
Enabling Deterministic Passive Quantum State Transfer with Giant Atoms
本文提出利用耦合到一维波导的巨型原子实现无源、确定性的量子态传输，通过优化耦合点位置和强度，在有限耦合点下达到高保真度，并分析了鲁棒性和色散补偿。
Quantum voting machine encoded with microwave photons
本文提出了一种基于微波光子量子比特编码的量子投票机，利用多控单靶量子相位门实现单步操作与可验证性，并保障投票者匿名性，数值模拟验证了其在当前量子技术下的可行性。
Classical-Quantum Dual Encoding for Laser Communications in Space
该研究提出一种经典-量子双编码方案，在激光通信中利用亚泊松噪声底实现量子密钥分发，同时保持经典数据传输，且安全层简单稳健，不影响经典速率。
Compressing Quantum Fisher Information
本文提出一种将量子 Fisher 信息压缩到单个量子比特的方法，并通过光子实验验证了两种压缩策略。
Modular Quantum Memories Using Passive Linear Optics and Coherent Feedback
本文提出利用被动线性光学和相干反馈实现单光子脉冲光学场中量子记忆的模块化方案，通过耦合两个衰减光学腔体构建隔离且抗退相干的内部模式，实现量子比特存储的写入/读出与存储模式切换，最终构建出多量子态量子记忆。
Tunable passive squeezing of squeezed light through unbalanced double homodyne detection
本文通过不平衡双锁模检测技术，实现对光子态的主动压缩或反压缩，展示了该方法在量子态操控与表征中的多功能性。
Identical particles as a genuine non-local resource
本文研究了全同粒子在Bell型实验中作为非定域资源的可能性，证明了几乎所有全同粒子状态都能在经典无源线性光学装置中展现非定域性，揭示了粒子不可区分性与Bell非定域性之间的联系。
Quantum synchronization via Active-Passive-Decomposition configuration: An open quantum system study
本文在开放量子系统框架下，通过主动-被动分解配置研究耗散量子谐振子的同步，证明在稳定与不稳定状态下均可实现完全同步，并在光机械装置中数值验证。
Passive Pauli Toggling of Polarization Qubits in Optical Fibers: Error Bounds and QKD Performance
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We present a bipartite two-level system coupled to electromagnetic quantum vacuum fluctuations through a general dipolar coupling. We derive the master equation in the framework of open quantum systems, assuming an environment composed of (i) solely vacuum fluctuations and (ii) the vacuum fluctuations and a conducting plate located at a fixed distance from the bipartite system. For both cases considered, we study the dynamics of the bipartite system and the temporal evolution of the concurrence of an initial entangled bipartite state. We further analyze the generation of entanglement due to th…
Deterministic quantum interactions between single photons and single quantum emitters are a vital building block towards the distribution of quantum information between remote systems. Deterministic photon-atom state transfer has been demonstrated by using protocols that include active feedback or synchronized control pulses. Here we demonstrate a completely passive swap gate between the states of a single photon and a single atom. The underlying mechanism is single-photon Raman interaction (SPRINT) - an interference-based effect in which a photonic qubit deterministically controls the state o…
Robustness of tripartite entangled states in passive PT-symmetric qubits
研究被动PT对称非厄米超导量子比特中由例外点诱导的三部分纠缠鲁棒性，发现全连接生成GHZ态、最近邻生成W态，且强Rabi频率与强耦合有助于维持纠缠。
The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work …
Tunable M-Ary Quantum Secure Direct Communication via Correlation-Histogram Modulation
提出基于双向纠缠的量子安全直接通信协议，信息编码为可调参数值，从检测对窗口的联合结果直方图解码，介绍协议级设计参数优势及防非理想效应泄漏的框架。
We demonstrate a platform for implementing quantum walks that overcomes many of the barriers associated with photonic implementations. We use coupled fiber-optic cavities to implement time-bin encoded walks in an integrated system. We show that this platform can achieve very low losses combined with high-fidelity operations, enabling an unprecedented large number of steps in a passive system, as required for scenarios with multiple walkers. Furthermore the platform is reconfigurable, enabling variation of the coin, and readily extends to multidimensional lattices. We demonstrate variation of t…
We propose and analyse a scheme for single-rail-encoded arbitrary multi-qubit quantum-state generation to provide a versatile tool for quantum optics and quantum information applications. Our scheme can be realized, for small numbers of qubits, with current technologies using single photon inputs, passive linear optics, and heralding measurements. The particular examples of two- and three-qubit cluster states are studied in detail. We show that such states can be prepared with a high probability of success. Our analysis quantifies the effects of experimentally relevant imperfections and ineffi…
We propose a method for the generation of a large variety of entangled states, encoded in the polarization degrees of freedom of N photons, within the same experimental setup. Starting with uncorrelated photons, emitted from N arbitrary single photon sources, and using linear optical tools only, we demonstrate the creation of all symmetric states, e.g., GHZ- and W-states, as well as all symmetric and non-symmetric total angular momentum eigenstates of the N qubit compound.
Characterizing symmetry-protected thermal equilibrium by work extraction
本研究证明在连通紧李群对称性约束下，量子态完全被动当且仅当为广义吉布斯系综，扩展了热平衡概念，为量子热机与电池设计及对称性热力学资源理论奠定基础。
Active error decoding and correction of topological quantum codes - in particular the toric code - remains one of the most viable routes to large scale quantum information processing. In contrast, passive error correction relies on the natural physical dynamics of a system to protect encoded quantum information. However, the search is ongoing for a completely satisfactory passive scheme applicable to locally-interacting two-dimensional systems. Here, we investigate dynamical decoders that provide passive error correction by embedding the decoding process into local dynamics. We propose a speci…
Well controlled and highly stable magnetic fields are desired for a wide range of applications in physical research, including quantum metrology, sensing, information processing, and simulation. Here we introduce a low-cost hybrid assembly of rare-earth magnets and magnetic field coils to generate a field strength of $\simeq\,10.9\,$mT with a spatial variation of less than 10$^{-6}$ within a diameter of spherical volume of $150\,$um. We characterise its tuneability and stability performance using a single Mg$^{+}$ atom confined in a radio-frequency surface-electrode trap under ultra-high vacuu…
Squeezed light is one of the resources of photonic quantum technology. Among the various nonlinear interactions capable of generating squeezing, the optical Kerr effect is particularly easy-to-use. A popular venue is to generate polarization squeezing, which is a special self-referencing variant of two-mode squeezing. To date, polarization squeezing generation setups have been very sensitive to fluctuations of external factors and have required careful tuning. In this work, we report on a development of a new all-fibre setup for polarization squeezing generation. The setup consists of passive …
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