Savona, Vincenzo

Date:   Thursday, June 10, 2021
Time:   10:00
Place:   scheduled Zoom meeting
Host:    Klaus Ensslin

Simulating open quantum systems: From classical to quantum algorithms

Vincenzo Savona
EPF Lausanne

The simulation of the dynamics and of the non-equilibrium steady state (NESS) of open quantum systems is a notoriously challenging task. In addition to the complexity intrinsic of many-body quantum systems, the non-unitary character of the generator of the dynamics and the lack of a rigorous variational principle constitute outstanding difficulties. Yet, in the era of Noisy Intermediate-Scale Quantum (NISQ) hardware, the access to accurate large scale simulations of open quantum systems may help improving the efficiency of advanced quantum algorithms and devising more advanced quantum error correction schemes. Here, I will present our latest results in the numerical simulation of the NESS of an open quantum system. I will first show how a time-dependent variational principle can be used to access the system dynamics through a positive-semidefined neural-network ansatz for the density matrix. I will then briefly review the existing proposals for quantum algorithms and will present a quantum algorithm, designed to run on fault-tolerant hardware, for the direct estimation of the NESS. I will conclude by discussing how a hybrid variational quantum algorithm may be designed to simulate the system dynamics of NISQ hardware.

1. Nagy, A. and Savona, V. Variational quantum Monte Carlo method with a neural-network ansatz for open quantum systems. Phys. Rev. Lett. 122, 250501 (2019).

2. Ramusat, N. and Savona, V. A quantum algorithm for the direct estimation of the steady state of open quantum systems. Quantum 5, 399 (2021).