近日，意大利的里雅斯特大学的Nicolò Piccione及其研究团队取得一项新进展。经过不懈努力，他们基于色散量子比特-光相互作用揭示自主测量中能量交换的基本机制。相关研究成果已于2024年6月14日在国际知名学术期刊《物理评论A》上发表。

该研究团队深入探讨了自主计量系统的动力学理论，特别是量子比特与一维波导中传播的光脉冲之间的色散相互作用。在这个过程中，光脉冲的相位会根据量子比特的状态发生位移，而量子比特哈密顿量的方向则具有任意性。由于这种相互作用具有色散性质，光子数得以守恒，但系统能量平衡的实现需通过光脉冲的光谱变形来实现。

基于解析和数值解，研究人员详细阐述了这种光谱变形的机制，并展示了它是如何补偿量子比特能量变化的。此外，他们还解释了输出光谱中三峰结构的形成原因，并给出了观测这一结构的条件。

据悉，测量不与量子系统的哈密顿量交换的可观测值通常会改变该系统的平均能量。在自主测量方案中，将系统耦合到量子计量器，系统的能量变化必须由量子计量器的能量变化来补偿。

附：英文原文

Title: Fundamental mechanisms of energy exchanges in autonomous measurements based on dispersive qubit-light interaction

Author: Nicolò Piccione, Maria Maffei, Xiayu Linpeng, Andrew N. Jordan, Kater W. Murch, Alexia Auffèves

Issue&Volume: 2024/06/14

Abstract: Measuring an observable which does not commute with the Hamiltonian of a quantum system usually modifies the mean energy of this system. In an autonomous measurement scheme, coupling the system to a quantum meter, the system's energy change must be compensated by the meter's energy change. Here, we theoretically study such an autonomous meter-system dynamics: a qubit interacting dispersively with a light pulse propagating in a one-dimensional waveguide. The phase of the light pulse is shifted, conditioned to the qubit's state along the direction, while the orientation of the qubit Hamiltonian is arbitrary. As the interaction is dispersive, photon number is conserved so that energy balance has to be attained by spectral deformations of the light pulse. Building on analytical and numerical solutions, we reveal the mechanism underlying this spectral deformation and display how it compensates for the qubit's energy change. We explain the formation of a three-peak structure of the output spectrum and we provide the conditions under which this is observable.

DOI: 10.1103/PhysRevA.109.063707

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.063707