We consider a quantum device $D$ interacting with a quantum many-body environment $R$ which features a second-order phase transition at $T=0$. Exploiting the description of the critical slowing down undergone by $R$ according to the Kibble-Zurek mechanism, we explore the possibility to freeze the environment in a configuration such that its impact on the device is significantly reduced. Within this framework, we focus upon the magnetic-domain formation typical of the critical behaviour in spin models, and propose a strategy that allows one to protect the entanglement between different components of $D$ from the detrimental effects of the environment.
Fujian Key Laboratory of Quantum Information and Quantum Optics, Fuzhou University（福州大学量子信息与量子光学福建省重点实验室）；Department of Physics, Fuzhou University（福州大学物理系）
Protection of Entanglement in the presence of Markovian or Non-Markovian Environment via particle velocity : Exact Results
在分析的基础上，研究了当量子系统处于马尔可夫或非马尔可夫环境中时，粒子速度对纠缠的保护作用的物理机制。特别是粒子速度的影响，检查在纠缠突然死亡（ESD）和纠缠复苏（ROE）现象。即使粒子快速运动，如果在零速度下发生，ESD现象也不会消失。然而，非零纠缠的时域$0 \leq t \leq t_*$随着速度的增加而变得越来越大。在零速度下发生ROE现象时，即使很小的速度也可以使这种现象不发生，但纠缠在时间上的振荡行为仍然保持不变。对于比较大的速度，振荡行为的振幅变得非常小。在这种情况下，纠缠可以通过粒子速度来保护。比较了速度对纠缠的保护和失谐量对纠缠的保护。
Quantum information encoded into superposition of coherent states is an illustrative representative of practical applications of macroscopic quantum coherence possessing. However, these states are very sensitive to energy loss, losing their non-classical aspects of coherence very rapidly. An available deterministic strategy to slow down this decoherence process is to apply a Gaussian squeezing transformation prior to the loss as a protective step. Here, we propose a deterministic hybrid protection scheme utilizing strong but feasible interactions with two-level ancillas immune to spontaneous e…
The inevitable dissipative interaction of an entangled quantum system with its environment causes degradation in quantum correlations present in the system. This can lead to a finite-time disappearance of entanglement, which is known as entanglement sudden death (ESD). Here, we consider an initially entangled qubit-qutrit system and a dissipative noise which leads to ESD, and propose a set of local unitary operations, which when applied on the qubit, qutrit, or both subsystems during the decoherence process, cause ESD to be hastened, delayed, or avoided altogether, depending on its time of app…
Quantum technologies able to manipulating single quantum systems, are presently developing. Among the dowries of the quantum realm, entanglement is one of the basic resources for the novel quantum revolution. Within this context, one is faced with the problem of protecting the entanglement when a system state is manipulated. In this paper, we investigate the effect of the classical driving field on the generation entanglement between two qubits interacting with a bosonic environment. We discuss the effect of the classical field on the generation of entanglement between two (different) qubits a…
Topological insulators combine insulating properties in the bulk with scattering-free transport along edges, supporting dissipationless unidirectional energy and information flow even in the presence of defects and disorder. The feasibility of engineering quantum Hamiltonians with photonic tools, combined with the availability of entangled photons, raises the intriguing possibility of employing topologically protected entangled states in optical quantum computing and information processing. However, while two-photon states built as a product of two topologically protected single-photon states …
High-fidelity quantum entanglement is a key resource for quantum communication and distributed quantum computing, enabling quantum state teleportation, dense coding, and quantum encryption. Any sources of decoherence in the communication channel however degrade entanglement fidelity, thereby increasing the error rates of entangled state protocols. Entanglement purification provides a method to alleviate these non-idealities, by distilling impure states into higher-fidelity entangled states. Here we demonstrate the entanglement purification of Bell pairs shared between two remote superconductin…
Evolution of tripartite entangled states in a decohering environment and their experimental protection using dynamical decoupling
我们开始了不同类别的三重纠缠态，即最大纠缠GHZ和W状态和${\rm W \bar{W}}$状态的实验保护的任务，使用动态解耦。这些状态是在一个三量子比特的NMR量子信息处理器上创建的，并允许在自然噪声的NMR环境中演化。在状态演化过程中的每个时刻，使用负性作为纠缠度量来监测三体纠缠。结果发现，W状态是最强大的，而GHZ型的国家是最脆弱的自然退相干存在于NMR系统。${\rm W \bar{W}}$态是GHZ类的，但以类似于W态的方式存储纠缠，令人惊讶的是，它比GHZ态更鲁棒。通过将主要噪声通道视为独立作用于每个量子比特的不相关相位阻尼通道以及广义振幅阻尼通道，可以最好地对实验数据进行建模。利用动态解耦，我们能够实现GHZ态纠缠的有效保护。W状态的状态保真度有微小的改善（其已经对自然系统退相干具有鲁棒性），而${\rm W \bar{W}}$状态在保真度和对退相干的保护方面显示出显著的改善。
Cryptography without Long-Term Quantum Memory and Global Entanglement: Classical Setups for One-Time Programs, Copy Protection, and Stateful Obfuscation
Silicon T centre hyperfine structure and memory protection schemes
Simon Fraser University（西蒙菲莎大学）；Photonic Inc.（Photonic公司）；Thayer School of Engineering, Dartmouth College（达特茅斯学院塔克工程学院）；Leibniz-Institut für Kris（莱布尼茨危机研究所）
The existence of $1/2$ modes in the entanglement spectrum (ES) has been shown to be a powerful quantum-informative signature of boundary states of gapped topological phases of matter, e.g., topological insulators and topological superconductors, where the finite bulk gap allows us to establish a crystal-clear correspondence between $1/2$ modes and boundary states. Here we investigate the recently proposed higher-order Weyl semimetals (HOWSM), where bulk supports gapless higher-order Weyl nodes and boundary supports hinge arcs and Fermi arcs. We find that the aim of unambiguously identifying hi…
Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences（奥地利科学院量子光学和量子信息研究所）；Faculty of Physics, University of Warsaw（华沙大学物理系）；Qilimanjaro Quantum Tech（基利马扎罗量子技术）
Recent experimental observation of weak ergodicity breaking in Rydberg atom quantum simulators has sparked interest in quantum many-body scars - eigenstates which evade thermalisation at finite energy densities due to novel mechanisms that do not rely on integrability or protection by a global symmetry. A salient feature of some quantum many-body scars is their sub-volume bipartite entanglement entropy. In this work we demonstrate that such exact many-body scars also possess extensive multipartite entanglement structure if they stem from an su(2) spectrum generating algebra. We show this analy…
We address the non-Markovian entanglement dynamics for bimodal continuous variable quantum systems interacting with two independent structured reservoirs. We derive an analytical expression for the entanglement of formation without performing the Markov and the secular approximations. We observe a variety of qualitative features such as entanglement sudden death, dynamical generation, and protection for two types of Lorentzian spectral densities, assuming the two modes initially excited in a twin-beam state. Our quantitative analysis shows that these cases with different reservoir spectrum, th…
In this paper, we investigate coherence protection of a quantum system coupled to a hierarchical environment by utilizing noise. As an example, we solve the Jaynes-Cummings (J-C) model in presence of both a classical and a quantized noise. The master equation is derived beyond the Markov approximation, where the influence of memory effects from both noises is taken into account. More importantly, we find that the performance of the coherence protection sensitively depends on the non-Markovian properties of both noises. By analyzing the mathematical mechanism of the coherence protection, we sho…
In this thesis, we report the theoretical and experimental investigations towards the creation, characterization, and manipulation of quantum entanglement in a photonic system. We examine two different aspects of quantum entanglement: In the first part, we discuss the experimental method for the preparation and characterization of SPDC-based polarization-entangled photon source. We provide a review study comparing different Entanglement Measures for non-maximally entangled two-qubit pure states and extend this analysis to higher-dimensional systems. In the second part, we study the entanglemen…
