Observation of quantum multi-Mpemba effect in a trapped-ion system

TL;DR

This paper reports the experimental observation of multiple quantum Mpemba effect trajectories in a trapped-ion system, revealing complex transient relaxation dynamics beyond traditional long-time explanations.

Contribution

It introduces the first experimental demonstration of multi-Mpemba effect in a quantum system with a novel theoretical framework based on relaxation speed.

Findings

Multiple trajectory crossings observed in quantum relaxation dynamics.

Initial states with larger overlap with the slowest decay mode can relax faster.

A phase diagram explains the occurrence and types of quantum Mpemba effects.

Abstract

The quantum Mpemba effect (ME) in Markovian systems is conventionally explained by a smaller overlap between the initial state and the slowest decay mode (SDM). Such state, initially farther away from equilibrium or steady state, relaxes faster than closer ones, resulting to a crossing of their trajectories. This picture, by neglecting the transient dynamics, holds in the long-time limit. Here we experimentally observe multiple trajectory crossings (multi-ME) in the relaxation dynamics of a trapped ion. Such novel dynamics takes place in a unusual scenario where the initial state instead has a larger overlap with the SDM. We develop a theoretical framework based on relaxation speed to understand the multi-ME. We show that the initial relaxation speed is governed by the fastest decay mode, which together with the SDM overlap gives a phase diagram that reveals both the occurrence and the types of quantum ME observed in our experiment. Our study goes beyond the simple picture based on the long-time limit, tracks continuously the quantum ME dynamics, and establishes a comprehensive framework to describe the transient quantum relaxation.