Universal, unambiguous concentration and distillation of Bell pairs
HUN-REN Wigner Research Centre for Physics（匈牙利科学院维格纳物理研究中心）；Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague（布拉格捷克理工大学核科学与物理工程学院）
Orsolya Kálmán, Aurél Gábris, Igor Jex, Tamás Kiss
The ability of preparing perfect Bell pairs with a practical scheme is of great relevance for quantum communication as well as distributed quantum computing. We propose a scheme which probabilistically, but unambiguously produces the $\left|Φ_{+}\right>$ Bell pair from four copies of qubit pairs initially in the same arbitrary pure quantum state. The same scheme, extended to eight qubit pairs initially in the same, moderately mixed quantum state, unambiguously produces the $\left|Φ_{+}\right>$ Bell pair with quadratically suppressed noise. The core step of the proposed scheme consists of a pair of local two-qubit operations applied at each of the two distant locations, followed by a partial projective measurement and postselection at each party, with results communicated classically. While the scheme resembles standard entanglement distillation protocols, it achieves success within just three iterations, making it attractive for real-world applications.
We propose and theoretically investigate an unambiguous Bell measurement of atomic qubits assisted by multiphoton states. The atoms interact resonantly with the electromagnetic field inside two spatially separated optical cavities in a Ramsey-type interaction sequence. The qubit states are postselected by measuring the photonic states inside the resonators. We show that if one is able to project the photonic field onto two coherent states on opposite sites of phase space, an unambiguous Bell measurement can be implemented. Thus our proposal may provide a core element for future components of q…
Unambiguous arbitrary high-dimensional Bell states analyzer via indefinite causal order
School of Mathematics and Physics, University of Science and Technology Beijing（北京科技大学数学与物理学院）；Department of Mathematics and Physics, Shijiazhuang Tiedao University（石家庄铁道大学数学与物理系）
Quantum information processing using linear optics is challenging due to the limited set of deterministic operations achievable without using complicated resource-intensive methods. While techniques such as the use of ancillary photons can enhance the information processing capabilities of linear optical systems they are technologically demanding. Therefore, determining the constraints posed by linear optics and optimizing linear optical operations for specific tasks under those constraints, without the use of ancillas, can facilitate their potential implementation. Here, we consider the task …
Generating optimal states for a homodyne Bell test
我们提出了一个协议，产生一个有条件的准备状态，可用于贝尔测试的基础上零差检测。基于Munro [PRA 1999]的结果，该状态对于基于使用相关光子数状态的正交相位零差测量的Bell不等式违反是接近最优的。该方案利用了Gaussian纠缠蒸馏协议的Schlemert等。[Annals of Phys.2004]，并且仅使用分束器和光电探测器从具有低压缩参数的双模压缩态源有条件地制备非高斯态，从而允许无环孔测试贝尔不等式。
Resource-adaptive distributed fault tolerance with very noisy Bell pairs
University of Bremen（不来梅大学）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）；University of Oxford（牛津大学）；German Research Center for Artificial Intelligence GmbH（德国人工智能研究中心有限公司）
We develop a scheme for generating a universal qubit cluster state using probabilistic Bell measurements without the need for feed-forward or long-time quantum memories. Borrowing ideas from percolation theory we numerically show that using unambiguous Bell measurements that succeed with 75% success probability, one could build a cluster state with an underlying pyrochlore geometry such that the probability of having a spanning cluster in a chosen direction approaches unity in the limit of an infinite lattice size. The initial resources required for the generation of a universal state in our p…
Quantum information processing in a modular architecture requires the distribution, stabilization and distillation of entanglement in a qubit network. We present autonomous entanglement stabilization protocols between two superconducting qubits that are coupled to distant cavities. The coupling between cavities is mediated and controlled via a three-wave mixing device that generates either a two-mode squeezed state or a delocalized mode between the remote cavities depending on the pump applied to the mixer. Local drives on the qubits and the cavities steer and maintain the system to the desire…
Bell state measurement is crucial to quantum information protocols, but it is impossible to unambiguously distinguish all the Bell states encoded in multi-photon using only linear optics. There is a maximum number of distinguished Bell states, i.e. distinguising limit which is very important for increasing the channel capacity of quantum communications. In this paper, we separate $n$-photon $D$-dimensional hyperentanglement into two groups. For the first group of $U$ ($G_1$), we obtain the limit ${N_1} = nD - (n - 1)$, which can be applied for both bosons' and fermions' cases. We further discu…
Entanglement distillation, an essential quantum information processing task, refers to the conversion from multiple copies of noisy entangled states to a smaller number of highly entangled states. In this work, we study the non-asymptotic fundamental limits for entanglement distillation. We investigate the optimal tradeoff between the distillation rate, the number of prepared states, and the error tolerance. First, we derive the one-shot distillable entanglement under completely positive partial transpose preserving operations as a semidefinite program and demonstrate an exact characterization…
We present a complete hyperentangled Bell state analysis protocol for two-photon four-qubit states which are simultaneously entangled in the polarization and time-bin degrees of freedom. The 16 hyperentangled states can be unambiguously distinguished via two steps. In the first step, the polarization entangled state is distinguished deterministically and nondestructively with the help of the cross-Kerr nonlinearity. Then, in the second step, the time-bin state is analyzed with the aid of the polarization entanglement. We also discuss the applications of our protocol for quantum information pro…
Entanglement boosting: Low-volume logical Bell pair preparation for distributed fault-tolerant quantum computation
Nanofiber Quantum Technologies, Inc. (NanoQT)（纳米纤维量子技术有限公司）；Clarendon Laboratory, University of Oxford（牛津大学克拉伦登实验室）；Department of Computer Science, Graduate School of Information Science and Technology, The University of Tokyo（东京大学大学院信息理工学研究系计算机科学专业）
A double selection entanglement distillation-based state estimator
Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）；S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心）；Keio University Shonan Fujisawa Campus（庆应义塾大学湘南藤泽校区）；National Institute of Informatics（国立情报学研究所）；SOKENDAI (The Graduate University for Advanced Studies)（综合研究大学院大学）；Faculty of Environment and Information Studies, Keio University Shonan Fujisawa Campus（庆应义塾大学湘南藤泽校区环境信息学部）
Entanglement distillation is a well-studied problem in quantum information, where one typically starts with $n$ noisy Bell pairs and distills $k$ Bell pairs of higher fidelity. While distilling Bell pairs is the canonical setting, it is important to study the distillation of multipartite entangled states because these can be useful for realizing distributed algorithms on quantum networks. In this paper, we study the distillation of GHZ states using quantum error correcting codes (QECCs). Using the stabilizer formalism, we begin by explaining the QECC-based Bell pair distillation protocol in ar…
Quantum Repeater Protocol using Quantum Error Correction for Distillation
Wyant College of Optical Sciences, University of Arizona（亚利桑那大学怀特光学科学学院）；Department of Electrical and Computer Engineering, University of Arizona（亚利桑那大学电气与计算机工程系）；Department of Electrical and Computer Engineering, University of Maryland, College Park（马里兰大学帕克分校电气与计算机工程系）
In the last decade Grice and Ewert and van Loock found linear optical networks achieving near-unit efficiency unambiguous Bell state discrimination, when fed with increasingly complex ancillary states. However, except for the vacuum ancilla case, the optimality of these schemes is unknown. Here, the optimality of these networks is investigated through analytical and numerical means. We show an analytical upper bound to the success probability for interferometers that preserve the polarization of the input photons, saturated by both Grice's and Evert-van Loock's strategies. Furthermore, such an…
The distribution of high-quality Greenberger-Horne-Zeilinger (GHZ) states is at the heart of many quantum communication tasks, ranging from extending the baseline of telescopes to secret sharing. They also play an important role in error-correction architectures for distributed quantum computation, where Bell pairs can be leveraged to create an entangled network of quantum computers. We investigate the creation and distillation of GHZ states out of non-perfect Bell pairs over quantum networks. In particular, we introduce a heuristic dynamic programming algorithm to optimize over a large class …
A Greenberger Horne Zeilinger (GHZ) entangled state with a phase is crucial for realizing desired multipartite quantum states for practical applications. Here, we report violations of the general Bell inequality (GBI) introduced in [1] using the four photon polarization entangled phase GHZ state realized via intrinsic polarization correlation and collective two-photon coherence in the 5S1/2 5P3/2 5D5/2 transition of 87Rb atoms. The phase GHZ state can be achieved by the unitary transformation of only one local phase of the four photons. Theoretically, the GHZ state with the π/4 phase affords m…
We compare the classification as entangled or separable of Bell diagonal bipartite qudits with positive partial transposition (PPT) and their properties for different dimensions. For dimension $d \geq 3$, a form of entanglement exists that is hard to detect and called bound entanglement due to the fact that such entangled states cannot be used for entanglement distillation. Up to this date, no efficient solution is known to differentiate bound entangled from separable states. We address and compare this problem named separability problem for a family of bipartite Bell diagonal qudits with spec…
Quantum non-locality tests have been of interest since the 1960's paper by Bell on the original EPR paradox.The present paper discusses whether the CGLMP (Bell) inequalities are possible tests for showing that quantum theory is not underpinned by local hidden variable theory (LHVT). It is found by applying Fine's theorem that the CGLMP approach involves a LHVT for the joint probabilities associated with the measurement of one observable from each of the two sub-systems, even though the underlying probabilities for joint measurements of all four observables may involve a non-local HVT. The latt…
Remote Entanglement in Lattice Surgery: To Distill, or Not to Distill
Duke University（杜克大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；North Carolina State University（北卡罗来纳州立大学）；University of California, Berkeley（加州大学伯克利分校）
Quantum networking relies on the management and exploitation of entanglement. Practical sources of entangled qubits are imperfect, producing mixed quantum state with reduced fidelity with respect to ideal Bell pairs. Therefore, an important primitive for quantum networking is entanglement distillation, whose goal is to enhance the fidelity of entangled qubits through local operations and classical communication (LOCC). Existing distillation protocols assume the availability of ideal, noiseless, communication channels. In this paper, we study the case in which communication takes place over noi…
East China Normal University（华东师范大学）；New York University Shanghai（纽约大学上海分校）；NYU-ECNU Institute of Physics at NYU Shanghai（纽约大学上海分校 NYU-ECNU 物理研究所）；Department of Physics, New York University（纽约大学物理系）
Linear optical realizations of Bell state measurement (BSM) on two single-photon qubits succeed with probability $p_s$ no higher than $0.5$. However pre-detection quadrature squeezing, i.e., quantum noise limited phase sensitive amplification, in the usual linear-optical BSM circuit, can yield ${p_s \approx 0.643}$. The ability to achieve $p_s > 0.5$ has been found to be critical in resource-efficient realizations of linear optical quantum computing and all-photonic quantum repeaters. Yet, the aforesaid value of $p_s > 0.5$ is not known to be the maximum achievable using squeezing, thereby lea…
Evaluation of Distimation's Real-world Performance on a Superconducting Quantum Computer
Faculty of Environment and Information Studies, Keio University Shonan Fujisawa Campus（庆应义塾大学湘南藤泽校区环境与信息学部）；Graduate School of Media and Governance, Keio University Shonan Fujisawa Campus（庆应义塾大学湘南藤泽校区媒体治理研究生院）；Quantum Computing Center, Keio University（庆应义塾大学量子计算中心）；Graduate School of Media Design, Keio University（庆应义塾大学媒体设计研究生院）；mercari R4D, Mercari, Inc.（Mercari公司mercari R4D）
