Koichi Yamazaki, Ranjith Nair, Horace P. Yuen
It is shown that the interactive error correction protocol `CASCADE' should be analyzed taking the correlation between passes and finite length of sequence into account. Furthermore we mention some problems in quantifying the reduction of Renyi entropy by information announced during the error correction process.
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Bounds on Petz-Rényi Divergences and their Applications for Device-Independent Cryptography
本文将变分方法应用于Petz-Rényi散度，结合完全Rényi熵累积定理提高了设备无关协议的有限尺寸密钥率，并推导出超越已知界限的DIQKD协议噪声容忍度。
It was first shown by Jacobs, in 2003, that the process of qubit state purification by continuous measurement of one observable can be enhanced, on average, by unitary feedback control. Here, we quantify this by the reduction in any one of the family of Rényi entropies $S_α$, with $0< α< \infty$, at some terminal time, revealing the rich structure of stochastic quantum control even for this simple problem. We generalize Jacobs' original argument, which was for (the unique) impurity measure with a linear evolution map under his protocol, by replacing linearity with convexity, thereby making it …
A realistic Quantum Key Distribution (QKD) protocol necessarily deals with finite resources, such as the number of signals exchanged by the two parties. We derive a bound on the secret key rate which is expressed as an optimization problem over Rényi entropies. Under the assumption of collective attacks by an eavesdropper, a computable estimate of our bound for the six-state protocol is provided. This bound leads to improved key rates in comparison to previous results.
Rényi security framework against coherent attacks applied to decoy-state QKD
本文提出了一个适用于相干攻击下固定和可变长度QKD协议的有限尺寸安全性证明框架，通过引入夹心条件Rényi熵评估等新数值技术，实现了更广的适用范围和更优的密钥率，特别是在小块尺寸下表现突出。
It is widely accepted in the quantum cryptography community that interactive information reconciliation protocols, such as cascade, are ineffcient due to the communication overhead. Instead, non-interactive information reconciliation protocols based on i.e. LDPC codes or, more recently, polar codes have been proposed. In this work, we argue that interactive protocols should be taken into consideration in modern quantum key distribution systems. In particular, we demonstrate how to improve the performance of cascade by proper implementation and use. Our implementation of cascade reaches a throu…
Measuring Rényi entropy with an Echo Protocol
提出基于回波型前向-后向演化序列的协议，通过跃迁概率表达纯度，高效测量第二Rényi熵，适用于量子多体系统，无需随机噪声平均。
Using Cascade in Quantum Key Distribution
针对采用 Cascade 双向纠错的 QKD 协议分析缺陷，提出修正方法以正确核算双向通信，产生有效密钥率，并在多种场景下验证其重要性。
We introduce a novel measure for the quantum property of nonstabilizerness - commonly known as "magic" - by considering the Rényi entropy of the probability distribution associated to a pure quantum state given by the square of the expectation value of Pauli strings in that state. We show that this is a good measure of nonstabilizerness from the point of view of resource theory and show bounds with other known measures. The stabilizer Rényi entropy has the advantage of being easily computable because it does not need a minimization procedure. We present a protocol for an experimental measureme…
The ladder configuration of atomic levels provides a source for telecom photons (signal) from the upper atomic transition. \ For rubidium and cesium atoms, the signal field has the range around 1.3-1.5 $μ$m that can be coupled to an optical fiber and transmitted to a remote location. \ Cascade emission may result in pairs of photons, the signal entangled with the subsequently emitted infrared photon (idler) from the lower atomic transition.\ This correlated two-photon source is potentially useful in the (Duan-Lukin-Cirac-Zoller) DLCZ protocol for the quantum repeater.\ We implement the cascade…
We investigate the problem of approximating the product $a^TBc$, where $a,c\in S^{n-1}$ and $B\in O_n$, in models of communication complexity and streaming algorithms. The worst meaningful approximation is to simply decide whether the product is 1 or -1, given the promise that it is either. We call that problem the aBc problem. This is a modification of computing approximate inner products, by allowing a basis change. While very efficient streaming algorithms and one-way communication protocols are known for simple inner products (approximating $a^Tc$) we show that no efficient one-way protoco…
Generalized Numerical Framework for Improved Finite-Sized Key Rates with Rényi Entropy
本文提出基于Rényi熵与散度的紧分析界，改进了密钥率优化框架，在高损耗低块大小情况下提升了性能，适用于长距离卫星协议。
Analytic Rényi Entropy Bounds for Device-Independent Cryptography
本文提出一种解析求解Rényi熵密钥率优化问题的方法，为基于CHSH博弈的设备无关密码协议获得更紧致的有限尺寸安全证明与密钥率。
Towards Scalable Quantum Key Distribution: A Machine Learning-Based Cascade Protocol Approach
针对量子密钥分发（QKD）可扩展性不足的问题，提出将机器学习自编码器与Cascade纠错协议结合的方法，可超99%准确率预测QBER和密钥长度，大幅降低纠错时间，提升QKD系统效率与实用性，为高吞吐量可扩展QKD树立新基准。
Generalized Rényi entropy accumulation theorem and generalized quantum probability estimation
本文提出新的熵积累界，改进有限大小性能，无需构造仿射min-tradeoff函数，适用于Rényi熵，实现全Rényi安全证明，同时拓展了量子概率估计与f加权Rényi熵框架。
We present a universal relation between the flow of a Renyi entropy and the full counting statistics of energy transfers. We prove the exact relation for a flow to a system in thermal equilibrium that is weakly coupled to an arbitrary time-dependent and non-equilibrium system. The exact correspondence, given by this relation, provides a simple protocol to quantify the flows of Shannon and Renyi entropies from the measurements of energy transfer statistics.
Cascade is an information reconciliation protocol proposed in the context of secret key agreement in quantum cryptography. This protocol allows removing discrepancies in two partially correlated sequences that belong to distant parties, connected through a public noiseless channel. It is highly interactive, thus requiring a large number of channel communications between the parties to proceed and, although its efficiency is not optimal, it has become the de-facto standard for practical implementations of information reconciliation in quantum key distribution. The aim of this work is to analyze…
Finite-size quantum key distribution rates from Rényi entropies using conic optimization
本文提出基于非对称锥优化的方法，解决条件瑞尼熵的优化问题，提升量子密钥分发的安全性和效率。
Enhanced Rényi Entropy-Based Post-Quantum Key Agreement with Provable Security and Information-Theoretic Guarantees
本文提出了一种基于瑞尼熵的后量子密钥协议，通过熵保持操作和秘密共享验证实现可证明安全性和信息论保证，提供 $2^{128}$ 的量子安全保证。
Autonomous stabilization of remote entanglement in a cascaded quantum network
该研究通过级联量子网络中的非互易波导耦合和局部驱动，实现了远程纠缠的自主稳定，展示了基于替代对称性的修改协议在提高纠缠度方面的有效性，为高保真度量子信息处理提供了新方法。
Performance of Cascade and LDPC-codes for Information Reconciliation on Industrial Quantum Key Distribution Systems
本研究分析、模拟、优化并比较了Cascade和结合Blind协议的LDPC码在现实工业量子密钥分发系统信息协调中的性能，并在实际工业QKD系统上验证了结果。
All incoherent as well as 2- and 3-qubit coherent eavesdropping strategies on the 6 state protocol of quantum cryptography are classified. For a disturbance of 1/6, the optimal incoherent eavesdropping strategy reduces to the universal quantum cloning machine. Coherent eavesdropping cannot increase Eve's Shannon information, neither on the entire string of bits, nor on the set of bits received undisturbed by Bob. However, coherent eavesdropping can increase as well Eve's Renyi information as her probability of guessing correctly all bits. The case that Eve delays the measurement of her probe u…
Credible-interval-based adaptive Bayesian quantum frequency estimation for entanglement-enhanced atomic clocks
本研究提出了一种基于可信区间的方法的自适应贝叶斯量子频率估计协议，用于增强纠缠的原子钟，实现了双海森堡极限精度扩展，同时扩展了动态范围并提高了稳定性。
Complete physical simulation of the entangling-probe attack on the BB84 protocol
本研究利用确定性单光子双量子比特量子逻辑，实现了针对 BB84 协议的最强单光子攻击，物理模拟了 Eve 访问 Bob 接收模块的真实攻击，实验结果与理论预测高度一致，证明了确定性量子逻辑在量子信息处理模拟中的实用性。
We propose using nonlinear Mach-Zehnder interferometer (NMZI) to efficiently prepare photonic quantum states from a classical input. We first analytically investigate the simple NMZI that can filtrate single photon state from weak coherent state by preferrentially blocking two-photon component. As a generalization, we show that the cascaded NMZI can deterministically extract arbitrary quantum state from a strong coherent state. Finally, we numerically demonstrate that the cascaded NMZI can be very efficient in both the input power and the level of cascade. The protocol of quantum state prepara…
This paper provides a security proof of the Bennett-Brassard (BB84) quantum key distribution protocol in practical implementation. To prove the security, it is not assumed that defects in the devices are absorbed into an adversary's attack. In fact, the only assumption in the proof is that the source is characterized. The proof is performed by lower-bounding adversary's Renyi entropy about the key before privacy amplification. The bound reveals the leading factors reducing the key generation rate.
Randomness is a vital resource for modern day information processing, especially for cryptography. A wide range of applications critically rely on abundant, high quality random numbers generated securely. Here we show how to expand a random seed at an exponential rate without trusting the underlying quantum devices. Our approach is secure against the most general adversaries, and has the following new features: cryptographic level of security, tolerating a constant level of imprecision in the devices, requiring only a unit size quantum memory per device component for the honest implementation,…
The Polyanskiy-Verdú paradigm provides an elegant way of using generalized-divergences to obtain strong converses and thus far has remained confined to protocols involving channels (classical or quantum). In this paper, drawing inspirations from it, we provide strong converses for protocols involving LOCC (local operations and classical communication). The key quantity that we work with is the Rényi relative entropy of entanglement. We provide a strong converse for the quantum state merging protocol that gives an exponential decay of the fidelity of the protocol for rates below the optimum wit…
We show how to measure the order-two Renyi entropy of many-body states of spinful fermionic atoms in an optical lattice in equilibrium and non-equilibrium situations. The proposed scheme relies on the possibility to produce and couple two copies of the state under investigation, and to measure the occupation number in a site- and spin-resolved manner, e.g. with a quantum gas microscope. Such a protocol opens the possibility to measure entanglement and test a number of theoretical predictions, such as area laws and their corrections. As an illustration we discuss the interplay between thermal a…
Quantifying non-stabilizerness via information scrambling
该研究提出了一种采样out-of-time-order correlator的方法，用于近似magic monotones和2-Renyi稳定子熵，解决了传统方法随量子比特数指数级扩展的问题，并在qubit和qutrit系统中验证了其有效性。
We develop a general theoretical framework for measurement protocols employing statistical correlations of randomized measurements. We focus on locally randomized measurements implemented with local random unitaries in quantum lattice models. In particular, we discuss the theoretical details underlying the recent measurement of the second Rényi entropy of highly mixed quantum states consisting of up to $10$ qubits in a trapped-ion quantum simulator [Brydges et al., Science 364, 260 (2019)]. We generalize the protocol to access the overlap of quantum states, prepared sequentially in an experime…
Towards Enhanced Quantum Resistance for RSA via Constrained Rényi Entropy Optimization: A Theoretical Framework for Backward-Compatible Cryptography
本文提出CREO框架，通过限制RSA素数接近度以优化瑞尼熵，提升RSA的量子抗性，同时保持向后兼容性。
The information reconciliation in a quantum key distribution protocol can be studied separately from other steps in the protocol. The problem of information reconciliation can be reduced to that of distributed source coding. Its solution by LDPC codes is reviewed. We list some obstacles preventing the LDPC-based distributed source coding from becoming a more favorable alternative to the Cascade protocol for information reconciliation in quantum key distribution protocols. This exposition does not require knowledge of the quantum theory.
Asymptotically tight security analysis of quantum key distribution based on universal source compression
本文提出一种新的PEC策略，实现渐近最优密钥率，通过构造基于量子侧信息的通用源压缩协议，结合集体攻击的缩减方法，紧密评估PEC失败概率，从而实现渐近紧安全性分析。
Apart from their foundational significance, entropic uncertainty relations play a central role in proving the security of quantum cryptographic protocols. Of particular interest are thereby relations in terms of the smooth min-entropy for BB84 and six-state encodings. Previously, strong uncertainty relations were obtained which are valid in the limit of large block lengths. Here, we prove a new uncertainty relation in terms of the smooth min-entropy that is only marginally less strong, but has the crucial property that it can be applied to rather small block lengths. This paves the way for a p…
Coupling the output of a source quantum system into a target quantum system is easily treated by cascaded systems theory if the intervening quantum channel is dispersionless. However, dispersion may be important in some transfer protocols, especially in solid-state systems. In this paper we show how to generalize cascaded systems theory to treat such dispersion, provided it is not too strong. We show that the technique also works for fermionic systems with a low flux, and can be extended to treat fermionic systems with large flux. To test our theory, we calculate the effect of dispersion on th…
Entanglement purification provides a unifying framework for proving the security of quantum key distribution schemes. Nonetheless, up till now, a local commutability constraint in the CSS code construction means that the error correction and privacy amplification procedures of BB84 are not fully decoupled. Here, I provide a method to decouple the two processes completely. The method requires Alice and Bob to share some initial secret string and use it to encrypt the bit-flip error syndrome using one-time-pad encryption. As an application, I prove the unconditional security of the interactive C…
Finite-Key Analysis of Quantum Key Distribution with Characterized Devices Using Entropy Accumulation
本文提出使用熵积累理论提升设备依赖型量子密钥分发的密钥速率，通过优化沙漏瑞尼熵并改进隐私放大方法。
Universal quantum coding
通过Schur-Weyl对偶性建立通用量子纠错原理，实现无需先验知识的纠缠提取与量子通信，达到最优速率与样本复杂度。
We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states, that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. The simultaneous interrogation of the laser phase with such a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the Ramsey interrogation time beyond the laser noise limit. We compare the new protocol with state of the art interrogation schemes, and show that entanglement all…
For the four-state protocol of quantum key distribution, optimum sets of probe parameters are calculated for the most general unitary probe in which each individual transmitted photon is made to interact with the probe so that the signal and the probe are left in an entangled state, and projective measurement by the probe, made subsequent to projective measurement by the legitimate receiver, yields information about the signal state. The probe optimization is based on maximizing the Renyi information gain by the probe on corrected data for a given error rate induced by the probe in the legitim…
Decoy state and purification protocols for superior quantum key distribution with imperfect quantum-dot based single photon sources: Theory and Experiment
本文提出并实验验证截断诱骗态与预告纯化两种QKD协议，利用不完美量子点单光子源的可控光子统计，使其最大可容忍信道损耗超过理想WCS逾3 dB。
Impact of dephased entangled states and varying measurement orientations on the reliability of cryptographic keys generated via the quantum protocol E91: A quantum simulation approach
本研究通过IBM Qiskit模拟E91量子密钥分发协议，分析输入态相位和偏振分析器方向对密钥可靠性的影响，发现激子寿命与精细结构劈裂之积是关键因素，且特定条件下协议可转化为BBM92协议。
We present an elementary derivation and generalisation of a recently reported method of simulating feedback in open quantum systems. We use our generalised method to simulate systems with multiple delays, as well as cascaded systems with delayed backscatter. In addition, we derive a generalisation of the quantum regression formula that applies to systems with delayed feedback, and show how to use the formula to compute two-time correlation functions of the system as well as output field properties. Finally, we show that delayed coherent feedback can be simulated as a quantum teleportation prot…
Non-stabilizerness in quantum-enhanced metrological protocols
该研究探讨了量子增强型计量协议中非稳定化性的产生与测量，揭示了其与多体关联和量子计量学的联系，并提出了一种实验量化非稳定化性的方法。
The rates of quantum cryptographic protocols are usually expressed in terms of a conditional entropy minimized over a certain set of quantum states. In particular, in the device-independent setting, the minimization is over all the quantum states jointly held by the adversary and the parties that are consistent with the statistics that are seen by the parties. Here, we introduce a method to approximate such entropic quantities. Applied to the setting of device-independent randomness generation and quantum key distribution, we obtain improvements on protocol rates in various settings. In partic…
Device-to-protocol simulation of spectrally-resolved quantum photonic circuits
本文提出PhoQuS框架，结合多类模型仿真量子光子电路，通过协方差-格拉姆约简降低读出成本，在连续、离散变量态制备中验证其性能，实现器件物理到协议级性能的关联。
Quantum key distribution (QKD) relies on quantum and classical procedures in order to achieve the growing of a secret random string -the key- known only to the two parties executing the protocol. Limited intrinsic efficiency of the protocol, imperfect devices and eavesdropping produce errors and information leakage from which the set of measured signals -the raw key- must be stripped in order to distill a final, information theoretically secure, key. The key distillation process is a classical one in which basis reconciliation, error correction and privacy amplification protocols are applied t…
Robust teleportation of a surface code and cascade of topological quantum phase transitions
本文提出用基本 Bell 测量隐形传态表面码态的鲁棒协议，将相干误差阈值映射为含 Nishimori 无序的 Ashkin–Teller 相变问题，并发现自对偶线上阈值发散。
How much secure randomness is in a quantum state?
针对量子态可提取密码学安全随机性的极限未解问题，研究基于含量子侧信息敌手的通用对抗模型，结合夹层Rényi熵推导紧致易算的安全随机性提取可达速率，为QRNG协议提供速率基准测试工具。
We show that a set of optical memories can act as a configurable linear optical network operating on frequency-multiplexed optical states. Our protocol is applicable to any quantum memories that employ off-resonant Raman transitions to store optical information in atomic spins. In addition to the configurability, the protocol also offers favourable scaling with an increasing number of modes where N memories can be configured to implement an arbitrary N-mode unitary operations during storage and readout. We demonstrate the versatility of this protocol by showing an example where cascaded memori…
A missing piece in quantum information theory, with very few exceptions, has been to provide the random coding exponents for quantum information-processing protocols. We remedy the situation by providing these exponents for a variety of protocols including those at the top of the family tree of protocols. Our line of attack is to provide an exponential bound on the decoupling error for a restricted class of completely positive maps where a key term in the exponent is in terms of a Rényi α-information-theoretic quantity for any α$\in$ (1,2]. Among the protocols covered are fully quantum Slepian…
Probing entanglement dynamics and topological transitions on noisy intermediate-scale quantum computers
本研究在IBM噪声中等规模量子计算机上模拟SSH链淬火动力学，用随机测量等方法测纠缠熵等物理量，结合误差缓解技术得到与精确解高度吻合的结果，为拓扑量子系统研究提供实验支撑。
Implementation of distillation protocols using a recirculating bricks mesh network
本文提出利用循环砖块网格架构实现量子信号处理所需的蒸馏协议，通过可编程光学系统降低计算资源消耗，并演示了级联量子干涉仪和傅里叶变换方案。
High-speed long-range quantum communication requires combining frequency multiplexed photonic channels with quantum memories. We experimentally demonstrate an integrated quantum frequency conversion protocol that can convert between wavelength division multiplexing channels in the telecom range with an efficiency of $55\pm 8\%$ and a noise subtracted HOM dip visibility of 84.5%. This protocol is based on a cascaded second order nonlinear interaction and can be used to interface a broad spectrum of frequencies with narrowband quantum memories, or alternatively as a quantum optical transponder, …
Refined sample complexities from the tomographic rate function
本文建立协变量子态层析协议分析框架，推导多种协议的速率函数并证明其严格排序，进而得出Wasserstein型样本复杂度的严格不等式，表明速率函数是比样本复杂度更精细的性能指标。
We investigate both experimentally and theoretically a simple yet more robust and flexible alternative to Rabi oscillation-type biexciton preparation protocols traditionally used for semiconductor quantum dots. The quantum dot is excited by a strong laser pulse positively detuned from the two-photon resonance yielding an on demand initialization of the biexciton state by making use of the phonon-induced thermalization of the photon dressed states. It is shown that for excitation pulses in the picosecond range, a stable and high fidelity of up to $f_{XX}=0.98\pm 0.01$ is reached. Notably, the g…
Dynamic rephasing in a telecom warm vapor quantum memory
本文提出动态重相位协议，通过转移存储激发到辅助退相干态，有效逆转积累的多普勒相位，将存储时间延长50倍，同时保持GHz带宽和低噪声，实现四独立时间-bin模式的on-demand存储与检索。
Capturing the Page Curve and Entanglement Dynamics of Black Holes in Quantum Computers
本研究在IBM超导量子计算机上检验量子比特传输模型，利用随机酉电路模拟黑洞scrambling动力学，并结合多体干涉与随机测量协议及量子误差缓解技术准确测定Rényi熵，展示了量子计算机研究黑洞Page曲线与纠缠动力学的实用性。
The recent direct experimental measurement of quantum entanglement paves the way towards a better understanding of many-body quantum systems and their correlations. Nevertheless, the experimental and theoretical advances had so far been predominantly limited to bosonic systems. Here, we study fermionic systems. Using experimental setups where multiple copies of the same state are prepared, arbitrary order Renyi entanglement entropies and entanglement negativities can be extracted by utilizing spatially-uniform beam splitters and on-site occupation measurement. As an example, we simulate the us…
Additivity and chain rules for quantum entropies via multi-index Schatten norms
通过推广多指标Schatten范数，建立了量子信道优化夹层Rényi熵的通用可加性，并推导了Rényi条件熵的链式法则，用于分析时间自适应量子密码协议。
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