近日，印度哈里什-钱德拉研究所的Ujjwal Sen及其研究团队取得一项新进展。经过不懈努力，他们揭示有限环境下量子制冷机中的瞬态效应。相关研究成果已于2025年1月13日在国际知名学术期刊《物理评论A》上发表。

该研究团队研究了一个由三个量子比特组成的小型量子制冷剂，每个量子比特都与一个环境保持接触。研究人员考虑了两种设置：一种是必然存在瞬态冷却的情况，另一种是稳态冷却和瞬态冷却都存在的情况。然而，研究人员主要关注点是瞬态冷却现象。研究表明，在瞬态区域内，通过将与冷量子比特相连的环境替换为由几个与冷量子比特相互作用的量子自旋构成的有限大小自旋环境，冷量子比特的温度可以比所有量子比特都连接到马尔可夫环境时进一步降低。

研究人员还考虑了使用多于一个有限大小自旋环境的三量子比特制冷装置进行制冷。不出所料，只有当至少有两个马尔可夫浴时，无论冷量子比特是否连接到环境，系统才能达到稳定温度。然而，在所有情况下都观察到了不同的温度振荡包络。他们研究了当一个、两个或所有马尔可夫浴被有限大小环境替换时，这些有限大小环境对冷量子比特冷却的影响。

此外，研究人员还在连接到一个或多个有限大小环境的两量子比特和单量子比特自持续装置中考察了这种影响。在推导连接到有限大小环境的量子比特的动力学方程时，研究人员没有对环境的马尔可夫性做出任何假设。因此，这些有限大小环境本质上表现出从环境到系统的信息回流，这是非马尔可夫性的标志。

因此，研究人员提出了一种目击者方法来检测此类系统中的非马尔可夫性。最后，他们研究了在存在马尔可夫噪声的情况下的冷却过程，并分析了噪声强度对制冷效果的影响。特别是，他们找到了制冷仍然可能的噪声强度上限。

附：英文原文

Title: Transient effects in quantum refrigerators with finite environments

Author: Aparajita Bhattacharyya¹, Ahana Ghoshal^1,2, and Ujjwal Sen¹

Issue&Volume: 2025-01-13

Abstract: We explore a small quantum refrigerator consisting of three qubits, each of which is kept in contact with an environment. We consider two settings: one is when there is necessarily transient cooling and the other is when both steady-state and transient coolings prevail. Our primary focus, however, is on the transient cooling phenomena. We show that in the transient regime, the temperature of the cold qubit can decrease further compared to the case where all qubits are connected to Markovian environments, by replacing the environment attached to the cold qubit with a finite-size spin environment, modeled by a few quantum spins interacting with the cold qubit. We also consider refrigeration with more than one finite-size spin environment of the three-qubit refrigerating device. As expected, a steady temperature is reached only if there are at least two Markovian baths, regardless of whether the cold qubit is attached to an environment. However, distinct envelopes of temperature oscillations are observed in all cases. We investigate the effects of the finite-size environments on the cooling of the cold qubit when one, two, or all Markovian baths are replaced by finite-size environments. Additionally, we examine this effect in two- and single-qubit self-sustained devices connected to one or more finite-size environments. In deriving the dynamical equations for the qubits connected to finite-size environments, we made no assumptions about the Markovian nature of the environment. As a result, these finite-size environments inherently exhibit information backflow from the environment to the system, a hallmark of non-Markovianity. Hence, we propose a witness to detect non-Markovianity in such systems. Finally, the cooling processes are studied in presence of Markovian noise, and we analyze the response on the refrigeration of the noise strength. In particular, we find the noise strength until which refrigeration remains possible.

DOI: 10.1103/PhysRevA.111.012209

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.111.012209