Quantum entanglement has been actively sought for in optomechanical and electromechanical systems. The simplest such system is a mechanical oscillator interacting with a coherent beam, while the oscillator also suffers from thermal decoherence. For this system, we show that quantum entanglement is always present between the oscillator and continuous outgoing fields -- even when the environmental temperature is high and the oscillator is highly classical. Such universal entanglement is also shown to be able to survive more than one oscillation cycle if characteristic frequency of the optomechanical interaction is larger than that of the thermal noise. Furthermore, we derive the effective optical mode that is maximally entangled with the oscillator, which will be useful for future quantum computing and encoding information into mechanical degrees of freedom.
Shannon Entropic Entanglement Criterion in the Simple Harmonic Oscillator
我们应用Walborn [Walborn S P，Taketani B G，Salles A，Toscano F和de Matos Filho R L 2009 Entropic Entanglement Criteria for Continuous Variables Phys.Rev.Lett.香农熵纠缠准则（SEEC），到简谐振子，一个通常在本科量子力学课程中讨论的系统。特别地，我们研究了耦合谐振子系统的纠缠。根据它们之间的相互作用，得到了一种简单的纠缠判据，表明当耦合强度较弱时，一对相互作用的基态耦合振子更容易纠缠，而当耦合强度较高时，处于激发态的耦合振子更容易纠缠.相互作用的振子随着相互作用的增加更有可能纠缠。
We study the effect of quantum entanglement maintained by virtual excitations in an ultrastrongly-coupled harmonic-oscillator system. Here, the quantum entanglement is caused by the counterrotating interaction terms and hence it is maintained by the virtual excitations. We obtain the analytical expression for the ground state of the system and analyze the relationship between the average excitation numbers and the ground-state entanglement. We also study the entanglement dynamics between the two oscillators in both the closed- and open-system cases. In the latter case, the quantum master equat…
We study entanglement dynamics in dispersive optomechanical systems consisting of two optical modes and a mechanical oscillator inside an optical cavity. The two optical modes interact with the mechanical oscillator, but not directly with each other. The appearance of optical entanglement witnesses non-classicality of the oscillator. We study the dependence of the entanglement dynamics with the optomechanical coupling, the mean photon number in the cavity and the oscillator temperature. An experimental realization with ultracold atomic ensembles is proposed.
In this work, we explore the dynamics of entanglement of an isolated quantum system consisting of two time-dependent, coupled harmonic oscillators. Through the use of a numerical method that relies on the estimation of the system's Wigner representation by a specific Gaussian function, we investigate the time evolution of the entanglement entropy after an instant quench in the inherent parameters of the system. Besides, from the comparison of the results obtained from the analytical expression for the time-dependent von Neumann entropy with the numerically computed entropy data, the effectiven…
Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator
本文计算了工作在阈值以上的三重共振非简并光学参量振荡器的三个输出场（泵浦场、信号场和闲频场）之间的量子关联。通过应用标准准则[P. van Loock和A. Furusawa，Phys.Rev.A67，052315（2003）]，我们表明，强三方连续变量纠缠存在于这个众所周知的和简单的系统。此外，由于纠缠直接由非线性过程产生，三个纠缠场可以具有非常不同的频率，为多色量子信息网络开辟了道路。
Dynamics of entanglement among the environment oscillators of many-body systems
在这项工作中，我们扩展了在参考文献[A]中开始的讨论。L.小德保拉，J. G. G.小德奥利维拉，J. G. Peixoto de Faria，Dagoberto S. Freitas和M. C.尼弥斯，{ \it Phys. Rev.} { \bf A89}，（2014）022303]来处理多体系统的并发动力学。在前一篇论文中，讨论的重点是系统分区之间的剩余纠缠。本文的目的是揭示环境振子间纠缠的动力学性质。本文考虑一个由一个谐振子与N个谐振子线性耦合组成的系统，并解析地求解了相应的动力学问题。我们将环境划分为任意两个分区，并量化了这些分区之间的纠缠动力学，结果表明，在每个分区中的激发相等的情况下，并发度达到值1，并且环境的两个分区是最大纠缠的。在很长一段时间内，主振子的激励被完全转移到环境振子中，环境振子纠缠。
Continuous variable entanglement in a cold-atoms mirrorless optical parametric oscillator
Universidade Federal de Pernambuco（伯南布哥联邦大学）；Instituto de Física da Universidade de São Paulo（圣保罗大学物理研究所）；Universidade Estadual da Paraíba（帕拉伊巴州立大学）；Universidade Federal do ABC（ABC联邦大学）
We present the measurement of entanglement between twin beams generated with a doubly resonant optical parameter oscillator (OPO) based on four-wave mixing in hot $^{85}$Rb vapor above threshold. This is the first measurement of entanglement in an OPO with $χ^{(3)}$ media above threshold. We reconstruct the covariance matrix for several configurations and with a full picture of the four side band mode state, we study entanglement between all possible bi-partitions. We show a robust generation of entanglement with stronger generation for a specific pair of modes. For this system, we show that a…
We study the dynamics and redistribution of entanglement and coherence in three time-dependent coupled harmonic oscillators. We resolve the Schrödinger equation by using time-dependent Euler rotation together with a linear quench model to obtain the state of vacuum solution. Such state can be translated to the phase space picture to determine the Wigner distribution. We show that its Gaussian matrix $\mathbb{G}(t)$ can be used to directly cast the covariance matrix $σ(t)$. To quantify the mixedness and entanglement of the state one uses respectively linear and von Neumann entropies for three c…
Localized electronic and nuclear spin qubits in the solid state constitute a promising platform for storage and manipulation of quantum information, even at room temperature. However, the development of scalable systems requires the ability to entangle distant spins, which remains a challenge today. We propose and analyze an efficient, heralded scheme that employs a parity measurement in a decoherence free subspace to enable fast and robust entanglement generation between distant spin qubits mediated by a hot mechanical oscillator. We find that high-fidelity entanglement at cryogenic and even …
Remote entanglement of massive oscillators via wire-mediated Coulomb interaction
Technical University of Vienna（维也纳工业大学）；Institute for Theoretical Physics and Vienna Center for Quantum Science and Technology, Technical University of Vienna（维也纳大学理论物理研究所与维也纳量子科学与技术中心）；Institute of Science and Technology Austria（奥地利科学技术研究所）
Exceptional point induced quantum phase synchronization and entanglement dynamics in mechanically coupled gain-loss oscillators
School of Nanoscience and Technology, IIT Kharagpur（IIT 哈格普尔理工学院纳米科学与技术学院）；Electronics and Electrical Communication Engineering Department, IIT Kharagpur（IIT 哈格普尔理工学院电子与电气通信工程系）；School of Natural and Computing Sciences, University of Aberdeen（阿伯丁大学自然与计算科学学院）
Laser cooled ions trapped in a linear Paul trap are long-standing ideal candidates for realizing quantum simulation, especially of many-body systems. The properties that contribute to this also provide the opportunity to demonstrate unexpected quantum phenomena in few-body systems. A pair of ions interacting in such traps exchange vibrational quanta through the Coulomb interaction. This linear interaction can be anharmonically modulated by an elementary coupling to the internal two-level structure of one of the ions. Driven by thermal energy in the passively coupled oscillators, which are them…
