Discrete-Time Controllability for Feedback Quantum Dynamics

A Quantum Model for Coherent Ising Machines: Discrete-time Measurement Feedback Formulation

Recently, the coherent Ising machine (CIM) as a degenerate optical parametric oscillator (DOPO) network has been researched to solve Ising combinatorial optimization problems. We formulate a theoretical model for the CIM with discrete-time measurement feedback processes, and perform numerical simulations for the simplest network, composed of two degenerate optical parametric oscillator pulses with the anti-ferromagnetic mutual coupling. We evaluate the extent to which quantum coherence exists during the optimization process.

横向磁场伊辛链的数字可控性

Digital controllability of transverse field Ising chains

研究通过离散的幺正操作实现精确基态，揭示数字方法与模拟方法的本质区别，核心贡献在于计算所需幺正操作数量与系统规模平方成正比。

Continuous and time-discrete non-Markovian system-reservoir interactions: Dissipative coherent quantum feedback in Liouville space

Based on tensor network realizations of path integrals reducing exponential memory scaling to polynomial efficiency and a Liouville space implementation of a time-discrete quantum memory, we investigate a quantum system simultaneously exposed to two structured reservoirs. For this purpose, we employ a numerically exact quasi-2D tensor network combining both diagonal and off-diagonal system-reservoir interactions with a twofold memory for continuous and discrete retardation effects. As a possible example, we study the non-Markovian dynamical interplay between discrete photonic feedback and stru…

Comparison between continuous- and discrete-mode coherent feedback for the Jaynes-Cummings model

Using the example of the Jaynes-Cummings model, we present a comparison between time-delayed coherent feedback mediated by reservoirs with continuous and discrete mode structures and work out their qualitative differences. In contrast to the discrete-mode case, the continuous-mode case results in the well-known single-delay dynamics which can, e.g., stabilize Rabi oscillations. The discrete-mode case, however, shows population trapping, not present in the continuous-mode model. Given these differences, we discuss the cavity output spectra and show how these characteristic properties are spectr…

离散量子反馈控制的拓扑

Topology of Discrete Quantum Feedback Control

本文发展了单粒子系统量子信道拓扑的一般框架，通过分类离散量子反馈控制的对称类，利用拓扑麦克斯韦妖构建了能抵抗噪声和退相干的拓扑反馈控制，为开放量子系统中非平衡拓扑相的创造与设计提供了新工具和指导原则。

Second Law of Thermodynamics with Discrete Quantum Feedback Control

A new thermodynamic inequality is derived which leads to the maximum work that can be extracted from multi-heat baths with the assistance of discrete quantum feedback control. The maximum work is determined by the free-energy difference and a generalized mutual information content between the thermodynamic system and the feedback controller. This maximum work can exceed that in conventional thermodynamics and, in the case of a heat cycle with two heat baths, the heat efficiency can be greater than that of the Carnot cycle. The consistency of our results with the second law of thermodynamics is…

Verifying detailed fluctuation relations for discrete feedback-controlled quantum dynamics

Discrete quantum feedback control consists of a managed dynamics according to the information acquired by a previous measurement. Energy fluctuations along such dynamics satisfy generalized fluctuation relations, which are useful tools to study the thermodynamics of systems far away from equilibrium. Due to the practical challenge to assess energy fluctuations in the quantum scenario, the experimental verification of detailed fluctuation relations in the presence of feedback control remains elusive. We present a feasible method to experimentally verify detailed fluctuation relations for discre…

通过零场金刚石量子模拟器中的单比特操作控制离散时间晶体

Controlling discrete time crystals via single-site operations in zero-field diamond quantum simulators

本研究提出在零场金刚石量子模拟器中通过单比特操作设计多种离散时间晶体协议，消除偏置磁场对处理器自旋可控性的限制，实现具有不同周期性和寿命的DTCs，为多功能量子模拟提供新平台。