On relations between stable and Zeno dynamics in a leaky graph decay model

Entangling photons via the quantum Zeno effect

The quantum Zeno effect describes the inhibition of quantum evolution by frequent measurements. Here, we propose a scheme for entangling two given photons based on this effect. We consider a linear-optics set-up with an absorber medium whose two-photon absorption rate $ξ_{2γ}$ exceeds the one-photon loss rate $ξ_{1γ}$. In order to reach an error probability $P_{\rm error}$, we need $ξ_{1γ}/ξ_{2γ}<2P_{\rm error}^2/π^2$, which is a factor of 64 better than previous approaches (e.g., by Franson et al). Since typical media have $ξ_{2γ}<ξ_{1γ}$, we discuss three mechanisms for enhancing two-photon …

Time evolution of condensed state of interacting bosons with reduced number fluctuation in a leaky box

We study the time evolution of the Bose-Einstein condensate of interacting bosons confined in a leaky box, when its number fluctuation is initially (t=0) suppressed. We take account of quantum fluctuations of all modes, including k = 0. We identify a ``natural coordinate'' b_0 of the interacting bosons, by which many physical properties can be simply described. Using b_0, we successfully define the cosine and sine operators for interacting many bosons. The wavefunction, which we call the ``number state of interacting bosons'' (NSIB), of the ground state that has a definite number N of interact…

Collective dynamics of multimode bosonic systems induced by weak quantum measurement

In contrast to the fully projective limit of strong quantum measurement, where the evolution is locked to a small subspace (quantum Zeno dynamics), or even frozen completely (quantum Zeno effect), the weak non-projective measurement can effectively compete with standard unitary dynamics leading to nontrivial effects. Here we consider global weak measurement addressing collective variables, thus preserving quantum superpositions due to the lack of which path information. While for certainty we focus on ultracold atoms, the idea can be generalized to other multimode quantum systems, including va…

利用纳米光子处理器实现真正的反事实通信

Genuine Counterfactual Communication with a Nanophotonic Processor

本文在可编程纳米光子处理器上实现了一种新协议，克服了先前反事实通信中弱痕迹和可扩展性问题，实现了无痕迹、低错误率（<1%）的真正反事实通信。

Accelerated and noise-resistant generation of a high-fidelity steady-state entanglement with Rydberg atoms

Based on Lyapunov control, a scheme is proposed to accelerate the dissipation dynamics for the generation of high-fidelity entanglement between two Rydberg atoms in the context of cavity quantum electrodynamics (QED). We first use the quantum Zeno dynamics and Rydberg antiblockade to find a unique steady state (two-atom singlet state) for the system. Then, applying additional coherent control (ACC) fields to improve the evolution speed of the dissipative system. The ACC fields are designed based on the target state and they vanish gradually along with increasing of the fidelity thus the system…

Correlation between Correlations: Process and Time in Quantum Networks

We study a special inhomogeneous quantum network consisting of a ring of $M$ pseudo-spins (here $M = 4$) sequentially coupled to one and the same central spin under the influence of given pulse sequences (quantum gate operations). This architecture could be visualized as a quantum Turing machine with a cyclic ``tape''. Rather than input-output-relations we investigate the resulting process, i.e. the correlation between one- and two-point expectation values (``correlations'') over various time-steps. The resulting spatio-temporal pattern exhibits many non-classical features including Zeno-effec…

Open system approach to the internal dynamics of a model multilevel molecule

A model multilevel molecule described by two sets of rotational internal energy levels of different parity and degenerate ground states, coupled by a constant interaction, is considered, by assuming that the random collisions in a gas of identical molecules, provoke transitions between adjacent energy levels of the same parity. The prescriptions of the continuous time quantum random walk are applied to the single molecule, interpreted as an open quantum system, and the master equation driving its internal dynamics is built for a general distribution of the waiting times between two consecutive…

Dicke time crystals in driven-dissipative quantum many-body systems

The Dicke model -- a paradigmatic example of superradiance in quantum optics -- describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system's dynamics are captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light-matter coupling can lead to time-crystalline-like behavior of the collective spin. In this work, we investigate whether such a Dicke time crystal is stable t…

开放量子系统中的稳定双极化子

Stable bipolarons in open quantum systems

该研究结合非马尔可夫纯态层级法、马尔可夫量子跳跃法与投影纯化密度矩阵重整化群，研究耗散环境下Hubbard-Holstein模型的输运与双极化子稳定性，发现耗散使双极化子局域化但结合能不受影响，为设计高$T_\mathrm{C}$超导材料提供启示。

逐步打开薛定谔的盒子揭示了一系列尖锐的动力学转变

Gradually opening Schrödinger's box reveals a cascade of sharp dynamical transitions

通过调节超导量子比特的测量强度，研究揭示了测量主导动力学通过三个尖锐转变从量子动力学中出现，退相干重新组织了这些转变的顺序。

具有零差测量的随机量子动力学的状态估计与控制：不确定性下的量子比特镇定

State Estimation and Control for Stochastic Quantum Dynamics with Homodyne Measurement: Stabilizing Qubits under Uncertainty

本文针对零差测量下具有不确定性的随机量子系统，提出基于李雅普诺夫切换控制的量子比特镇定方法，并通过多模型估计与状态重建保证概率意义下的实际稳定。