Seminar on current topics in quantum thermodynamics
Dr. Géraldine Haack
Location
Online
Seminar on current topics in quantum thermodynamics – Online Event
Date & Time
February 10, 2022, 9:00 am – 10:30 am
Description
Title: Non-Hermitian physics for controlling quantum transport in nanoscale devices
Open quantum systems have a natural connection to non-Hermitian physics. Their time evolution, captured by the Liouvillian, usually accounts for a free Hamiltonian evolution (i.e., Hermitian contribution) and for dissipation due to coupling to the reservoirs, this one being clearly non- Hermitian. A hallmark of non-Hermitian physics is the possibility for the system to reach exceptional points (EPs); dissipative open quantum systems can therefore exhibit Liouvillian EPs (to be contrasted to Hamiltonian EPs that can appear in a closed quantum system described by a non-Hermitian Hamiltonian). By definition, EPs are specific points in parameter space at which two or more eigenvalues of a non-Hermitian matrix and their corresponding eigenvectors coalesce. Recently, Hamiltonian EPs have attracted lots of interest in the context of quantum sensing and have been demonstrated experimentally on photonics and superconducting platforms by engineering non-Hermitian Hamiltonians.
In contrast, Liouvillian EPs have only been discussed for simple systems, such as a single dissipative spin or in the absence of quantum jumps, i.e., considering a semiclassical approach to the dynamics. Open questions concern the search for Hamiltonian and Liouvillian EPs in state- of-the-art physical platforms and their signatures, especially in the quantum regime. In this talk, I will present recent results considering a minimal model for an open quantum system made of two Interacting quantum systems. We solve analytically the dynamics of this non- Hermitian quantum system. We demonstrate the existence of Liouvillian EPs for an experimentally accessible range of parameters. We uncover a signature of EPs in the long-time dynamics, in the form of critical decay towards the steady state, in analogy to critical damping in a classical harmonic oscillator. These results broaden the class of systems exhibiting EPs and opens new routes for controlling the quantum dynamics of out-of-equilibrium nanoscale devices.
Reference:
S. Khandelwal, N. Brunner, G. Haack, PRX Quantum 2, 040346 (2021)