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Network-Device-Independent Certification of Causal Nonseparability 独立于网络设备的因果不可分性认证
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-30 DOI: 10.22331/q-2024-10-30-1514
Hippolyte Dourdent, Alastair A. Abbott, Ivan Šupić, Cyril Branciard
Causal nonseparability is the property underlying quantum processes incompatible with a definite causal order. So far it has remained a central open question as to whether any process with a clear physical realisation can violate a causal inequality, so that its causal nonseparability can be certified in a device-independent way, as originally conceived. Here we present a method solely based on the observed correlations, which certifies the causal nonseparability of all the processes that can induce a causally nonseparable distributed measurement in a scenario with trusted quantum input states, as defined in [Dourdent et al., Phys. Rev. Lett. 129, 090402 (2022)]. This notably includes the celebrated quantum switch. This device-independent certification is achieved by introducing a network of untrusted operations, allowing one to self-test the quantum inputs on which the effective distributed measurement induced by the process is performed.
因果不可分性是量子过程与确定的因果顺序不相容的基本属性。迄今为止,一个核心的悬而未决的问题是,是否任何具有明确物理现实的过程都能违反因果不等式,从而使其因果不可分性能像最初设想的那样以一种与设备无关的方式得到证明。在这里,我们提出了一种完全基于观测到的相关性的方法,它可以证明所有过程的因果不可分割性,这些过程可以在具有可信量子输入状态的情况下引起因果不可分割的分布式测量,正如[Dourdent 等人,Phys. Rev. Lett.这主要包括著名的量子开关。这种独立于设备的认证是通过引入一个非信任操作网络来实现的,它允许人们对量子输入进行自我测试,在量子输入上执行由过程诱导的有效分布式测量。
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引用次数: 0
Comment on “Multivariable quantum signal processing (M-QSP): prophecies of the two-headed oracle” 关于 "多变量量子信号处理(M-QSP):双头神谕的预言 "的评论
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-29 DOI: 10.22331/q-2024-10-29-1512
Hitomi Mori, Kaoru Mizuta, Keisuke Fujii
Multivariable Quantum Signal Processing (M-QSP) [1] is expected to provide an efficient means to handle polynomial transformations of multiple variables simultaneously. However, we identified several inconsistencies in the main theorem, where necessary and sufficient conditions for achievable polynomials are provided, and its proof in Ref. [1]. Moreover, a counterexample to the conjecture in Ref. [1], based on which the main theorem is constructed, is presented in Ref. [2], meaning the requirement of the conjecture should be included as a condition in the theorem. Here we note our observations and propose the revised necessary conditions for M-QSP. We also show that these necessary conditions cannot be sufficient conditions, and thus some additional condition on top of these revisions is essentially required for the complete M-QSP theorem.
多变量量子信号处理(M-QSP)[1] 被认为是同时处理多变量多项式变换的有效方法。然而,我们发现主定理(其中提供了可实现多项式的必要条件和充分条件)与参考文献[1]中的证明存在若干不一致之处。[1].此外,参考文献[1]中的猜想有一个反例。[1] 中猜想的反例,并在此基础上构建了主定理。[2],这意味着猜想的要求应作为条件包含在定理中。在此,我们指出了我们的观察结果,并提出了修改后的 M-QSP 必要条件。我们还证明了这些必要条件不可能是充分条件,因此在这些修订的基础上还需要一些附加条件才能得到完整的 M-QSP 定理。
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引用次数: 0
Universal quantum processors in spin systems via robust local pulse sequences 通过鲁棒局部脉冲序列实现自旋系统中的通用量子处理器
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-29 DOI: 10.22331/q-2024-10-29-1513
Matteo Votto, Johannes Zeiher, Benoît Vermersch
We propose a protocol to realize quantum simulation and computation in spin systems with long-range interactions. Our approach relies on the local addressing of single spins with external fields parametrized by Walsh functions. This enables a mapping from a class of target Hamiltonians, defined by the graph structure of their interactions, to pulse sequences. We then obtain a recipe to implement arbitrary two-body Hamiltonians and universal quantum circuits. Performance guarantees are provided in terms of bounds on Trotter errors and total number of pulses. Additionally, Walsh pulse sequences are shown to be robust against various types of pulse errors, in contrast to previous hybrid digital-analog schemes of quantum computation. We demonstrate and numerically benchmark our protocol with examples from the dynamics of spin models, quantum error correction and quantum optimization algorithms.
我们提出了一种在具有长程相互作用的自旋系统中实现量子模拟和计算的协议。我们的方法依赖于用沃尔什函数参数化的外部场对单个自旋进行局部寻址。这就实现了从一类目标哈密顿(由其相互作用的图结构定义)到脉冲序列的映射。然后,我们获得了实现任意二体哈密顿和通用量子电路的方法。我们从特罗特误差和脉冲总数的界限方面提供了性能保证。此外,与之前的量子计算数模混合方案相比,沃尔什脉冲序列对各种类型的脉冲误差具有鲁棒性。我们以自旋模型动力学、量子纠错和量子优化算法为例,演示了我们的协议并对其进行了数值基准测试。
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引用次数: 0
Hardness results for decoding the surface code with Pauli noise 利用保利噪声解码面码的难度结果
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-28 DOI: 10.22331/q-2024-10-28-1511
Alex Fischer, Akimasa Miyake
Real quantum computers will be subject to complicated, qubit-dependent noise, instead of simple noise such as depolarizing noise with the same strength for all qubits. We can do quantum error correction more effectively if our decoding algorithms take into account this prior information about the specific noise present. This motivates us to consider the complexity of surface code decoding where the input to the decoding problem is not only the syndrome-measurement results, but also a noise model in the form of probabilities of single-qubit Pauli errors for every qubit.

In this setting, we show that quantum maximum likelihood decoding (QMLD) and degenerate quantum maximum likelihood decoding (DQMLD) for the surface code are NP-hard and #P-hard, respectively. We reduce directly from SAT for QMLD, and from #SAT for DQMLD, by showing how to transform a boolean formula into a qubit-dependent Pauli noise model and set of syndromes that encode the satisfiability properties of the formula. We also give hardness of approximation results for QMLD and DQMLD. These are worst-case hardness results that do not contradict the empirical fact that many efficient surface code decoders are correct in the average case (i.e., for most sets of syndromes and for most reasonable noise models). These hardness results are nicely analogous with the known hardness results for QMLD and DQMLD for arbitrary stabilizer codes with independent $X$ and $Z$ noise.
真正的量子计算机将受到复杂的、依赖于量子比特的噪声的影响,而不是简单的噪声,如所有量子比特强度相同的去极化噪声。如果我们的解码算法能考虑到有关特定噪声的先验信息,我们就能更有效地进行量子纠错。这促使我们考虑表面代码解码的复杂性,在这种情况下,解码问题的输入不仅是综合征测量结果,还有以每个量子比特的单量子比特保利误差概率为形式的噪声模型。在这种情况下,我们证明表面码的量子极大似然解码(QMLD)和退化量子极大似然解码(DQMLD)分别是 NP 难和 #P 难。我们通过展示如何将布尔公式转化为依赖于量子比特的保利噪声模型和编码该公式的可满足性属性的综合征集,直接从 SAT 对 QMLD 进行了简化,并从 #SAT 对 DQMLD 进行了简化。我们还给出了 QMLD 和 DQMLD 的近似硬度结果。这些都是最坏情况下的硬度结果,与许多高效表面代码解码器在平均情况下(即对于大多数联合集和大多数合理噪声模型)都是正确的这一经验事实并不矛盾。这些硬度结果与已知的 QMLD 和 DQMLD 的硬度结果非常相似,它们适用于具有独立 $X$ 和 $Z$ 噪声的任意稳定器代码。
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引用次数: 0
Deterministic Bethe state preparation 确定性贝特态准备
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-24 DOI: 10.22331/q-2024-10-24-1510
David Raveh, Rafael I. Nepomechie
We present an explicit quantum circuit that prepares an arbitrary $U(1)$-eigenstate on a quantum computer, including the exact eigenstates of the spin-$1/2 XXZ$ quantum spin chain with either open or closed boundary conditions. The algorithm is deterministic, does not require ancillary qubits, and does not require QR decompositions. The circuit prepares such an $L$-qubit state with $M$ down-spins using $binom{L}{M}-1$ multi-controlled rotation gates and $2M(L-M)$ CNOT-gates.
我们提出了一种明确的量子电路,可在量子计算机上准备任意 $U(1)$ 特征状态,包括具有开放或封闭边界条件的自旋-$1/2 XXZ$ 量子自旋链的精确特征状态。该算法是确定性的,不需要辅助量子位,也不需要 QR 分解。该电路使用 $binom{L}{M}-1$ 多控旋转门和 $2M(L-M)$ CNOT 门来准备这样一个具有 $M$ 下旋的 $L$ 量子位态。
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引用次数: 0
Limitations for Quantum Algorithms to Solve Turbulent and Chaotic Systems 量子算法解决湍流和混沌系统的局限性
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-24 DOI: 10.22331/q-2024-10-24-1509
Dylan Lewis, Stephan Eidenbenz, Balasubramanya Nadiga, Yiğit Subaşı
We investigate the limitations of quantum computers for solving nonlinear dynamical systems. In particular, we tighten the worst-case bounds of the quantum Carleman linearisation (QCL) algorithm [Liu et al., PNAS 118, 2021] answering one of their open questions. We provide a further significant limitation for any quantum algorithm that aims to output a quantum state that approximates the normalized solution vector. Given a natural choice of coordinates for a dynamical system with one or more positive Lyapunov exponents and solutions that grow sub-exponentially, we prove that any such algorithm has complexity scaling at least exponentially in the integration time. As such, an efficient quantum algorithm for simulating chaotic systems or regimes is likely not possible.
我们研究了量子计算机在求解非线性动力学系统方面的局限性。特别是,我们收紧了量子卡勒曼线性化(QCL)算法[Liu 等人,PNAS 118, 2021]的最坏情况边界,回答了其中一个开放性问题。我们为任何旨在输出近似归一化解向量的量子态的量子算法提供了进一步的重要限制。给定一个具有一个或多个正 Lyapunov 指数且解呈亚指数增长的动力学系统的自然选择坐标,我们证明任何此类算法的复杂度都至少以积分时间的指数级缩放。因此,模拟混沌系统或机制的高效量子算法很可能是不可能的。
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引用次数: 0
Quantum networks theory 量子网络理论
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-23 DOI: 10.22331/q-2024-10-23-1508
Pablo Arrighi, Amélia Durbec, Matt Wilson
The formalism of quantum theory over discrete systems is extended in two significant ways. First, quantum evolutions are generalized to act over entire network configurations, so that nodes may find themselves in a quantum superposition of being connected or not, and be allowed to merge, split and reconnect coherently in a superposition. Second, tensors and traceouts are generalized, so that systems can be partitioned according to almost arbitrary logical predicates in a robust manner. The hereby presented mathematical framework is anchored on solid grounds through numerous lemmas. Indeed, one might have feared that the familiar interrelations between the notions of unitarity, complete positivity, trace-preservation, non-signalling causality, locality and localizability that are standard in quantum theory be jeopardized as the neighbourhood and partitioning between systems become both quantum, dynamical, and logical. Such interrelations in fact carry through, albeit two new notions become instrumental: consistency and comprehension.
关于离散系统的量子理论的形式主义在两个重要方面得到了扩展。首先,量子演化被泛化为作用于整个网络配置,因此节点可以发现自己处于连接或不连接的量子叠加状态,并可以在叠加状态下连贯地合并、分裂和重新连接。其次,对张量和迹线进行了泛化,从而可以根据几乎任意的逻辑谓词,以稳健的方式对系统进行分割。本文提出的数学框架通过大量寓言建立在坚实的基础之上。事实上,人们可能会担心,量子理论中标准的单元性、完全实在性、轨迹保留、非信号因果性、局域性和局域性等概念之间熟悉的相互关系,会因为系统之间的邻域和分区变得既是量子的、动态的,又是逻辑的而受到损害。尽管有两个新的概念变得非常重要:一致性和理解性,但这种相互关系实际上是贯穿始终的。
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引用次数: 0
Programmable adiabatic demagnetization for systems with trivial and topological excitations 具有三态和拓扑激发的系统的可编程绝热消磁
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-23 DOI: 10.22331/q-2024-10-23-1505
Anne Matthies, Mark Rudner, Achim Rosch, Erez Berg
We propose a simple, robust protocol to prepare a low-energy state of an arbitrary Hamiltonian on a quantum computer or programmable quantum simulator. The protocol is inspired by the adiabatic demagnetization technique, used to cool solid-state systems to extremely low temperatures. A fraction of the qubits (or spins) is used to model a spin bath that is coupled to the system. By an adiabatic ramp down of a simulated Zeeman field acting on the bath spins, energy and entropy are extracted from the system. The bath spins are then measured and reset to the polarized state, and the process is repeated until convergence to a low-energy steady state is achieved. We demonstrate the protocol via application to the quantum Ising model. We study the protocol's performance in the presence of noise and show how the information from the measurement of the bath spins can be used to monitor the cooling process. The performance of the algorithm depends on the nature of the excitations of the system; systems with non-local (topological) excitations are more difficult to cool than those with local excitations. We explore the possible mitigation of this problem by trapping topological excitations.
我们提出了一种简单、稳健的协议,用于在量子计算机或可编程量子模拟器上制备任意哈密顿的低能态。该协议受绝热消磁技术的启发,该技术用于将固态系统冷却到极低的温度。一部分量子比特(或自旋)被用来模拟与系统耦合的自旋浴。通过作用于自旋浴的模拟泽曼场的绝热降温,从系统中提取能量和熵。然后测量浴池自旋并将其重置为极化状态,并重复该过程,直到收敛到低能量稳态。我们将该协议应用于量子伊辛模型。我们研究了该协议在存在噪声时的性能,并展示了如何利用测量浴池自旋的信息来监控冷却过程。该算法的性能取决于系统激发的性质;具有非局部(拓扑)激发的系统比具有局部激发的系统更难冷却。我们探讨了通过捕获拓扑激元来缓解这一问题的可能性。
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引用次数: 0
Option pricing under stochastic volatility on a quantum computer 量子计算机随机波动下的期权定价
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-23 DOI: 10.22331/q-2024-10-23-1504
Guoming Wang, Angus Kan
We develop quantum algorithms for pricing Asian and barrier options under the Heston model, a popular stochastic volatility model, and estimate their costs, in terms of T-count, T-depth and number of logical qubits, on instances under typical market conditions. These algorithms are based on combining well-established numerical methods for stochastic differential equations and quantum amplitude estimation technique. In particular, we empirically show that, despite its simplicity, weak Euler method achieves the same level of accuracy as the better-known strong Euler method in this task. Furthermore, by eliminating the expensive procedure of preparing Gaussian states, the quantum algorithm based on weak Euler scheme achieves drastically better efficiency than the one based on strong Euler scheme. Our resource analysis suggests that option pricing under stochastic volatility is a promising application of quantum computers, and that our algorithms render the hardware requirement for reaching practical quantum advantage in financial applications less stringent than prior art.
我们开发了海斯顿模型(一种流行的随机波动模型)下的亚洲期权和障碍期权定价量子算法,并在典型市场条件下的实例中估算了这些算法的成本(T-计数、T-深度和逻辑量子比特数)。这些算法的基础是将成熟的随机微分方程数值方法与量子振幅估算技术相结合。特别是,我们通过经验证明,尽管弱欧拉法很简单,但在这项任务中却能达到与更著名的强欧拉法相同的精度水平。此外,由于省去了准备高斯状态这一昂贵的过程,基于弱欧拉方案的量子算法比基于强欧拉方案的算法实现了更高的效率。我们的资源分析表明,随机波动下的期权定价是量子计算机的一个有前途的应用,我们的算法使得在金融应用中实现实际量子优势的硬件要求比现有技术更宽松。
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引用次数: 0
Quantum Universally Composable Oblivious Linear Evaluation 量子普遍可复合遗忘线性评估
IF 6.4 2区 物理与天体物理 Q1 PHYSICS, MULTIDISCIPLINARY Pub Date : 2024-10-23 DOI: 10.22331/q-2024-10-23-1507
Manuel B. Santos, Paulo Mateus, Chrysoula Vlachou
Oblivious linear evaluation is a generalization of oblivious transfer, whereby two distrustful parties obliviously compute a linear function, $f (x) = ax + b$, i.e., each one provides their inputs that remain unknown to the other, in order to compute the output $f (x)$ that only one of them receives. From both a structural and a security point of view, oblivious linear evaluation is fundamental for arithmetic-based secure multi-party computation protocols. In the classical case, oblivious linear evaluation protocols can be generated using oblivious transfer, and their quantum counterparts can, in principle, be constructed as straightforward extensions using quantum oblivious transfer. Here, we present the first, to the best of our knowledge, quantum protocol for oblivious linear evaluation that, furthermore, does not rely on quantum oblivious transfer. We start by presenting a semi-honest protocol, and then extend it to the dishonest setting employing a $commit-and-open$ strategy. Our protocol uses high-dimensional quantum states to obliviously compute $f (x)$ on Galois Fields of prime and prime-power dimension. These constructions utilize the existence of a complete set of mutually unbiased bases in prime-power dimension Hilbert spaces and their linear behaviour upon the Heisenberg-Weyl operators. We also generalize our protocol to achieve vector oblivious linear evaluation, where several instances of oblivious linear evaluation are generated, thus making the protocol more efficient. We prove the protocols to have static security in the framework of quantum universal composability.
遗忘线性评估是对遗忘转移的一种概括,即两个互不信任的当事人遗忘地计算一个线性函数 $f (x) = ax + b$,也就是说,每一方提供自己的输入,另一方保持未知,以计算只有其中一方收到的输出 $f(x)$。从结构和安全的角度来看,遗忘线性评估对于基于算术的安全多方计算协议都是至关重要的。在经典情况下,遗忘线性评估协议可以通过遗忘转移生成,而它们的量子对应协议原则上可以通过量子遗忘转移直接扩展。据我们所知,我们在这里提出了第一个用于遗忘线性评估的量子协议,而且不依赖于量子遗忘传输。我们首先提出了一个半诚实协议,然后采用 "提交-打开 "策略将其扩展到不诚实环境。我们的协议使用高维量子态在素数维和素幂数维的伽罗瓦场上遗忘计算 $f (x)$。这些构造利用了素幂维度希尔伯特空间中存在的一套完整的互不偏倚基,以及它们在海森堡-韦尔算子上的线性行为。我们还对协议进行了扩展,以实现矢量遗忘线性评估,即生成多个遗忘线性评估实例,从而提高协议的效率。我们证明了协议在量子通用可组合性框架下的静态安全性。
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引用次数: 0
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