Steady-State Nonlinear Many-Body Quantum Transport

Elham Khosravi, Stefan Kurth, Gianluca Stefanucci +1 more

Gianluca Stefanucci, Stefan Kurth, David Jacob +1 more

Peter Bokes, Rex W. Godby

We develop a theoretical framework for describing steady-state quantum transport phenomena, based on the general maximum-entropy principle of nonequilibrium statistical mechanics. The general form of the many-body density matrix is derived, which contains the invariant part of the current operator that guarantees the nonequilibrium and steady-state character of the ensemble. Several examples of the theory are given, demonstrating the relationship of the present treatment to the widely used scattering-state occupation schemes at the level of the self-consistent single-particle approximation. The latter schemes are shown not to maximize the entropy, except in certain limits.

Klée Pollock

Leonardo Lauck, Aurea Rosas Vasconcellos, Roberto Luzzi

Pengfei Zhang, Yu Gao, Xiansong Xu +29 more

Non-equilibrium quantum transport is crucial to technological advances ranging from nanoelectronics to thermal management. In essence, it deals with the coherent transfer of energy and (quasi-)particles through quantum channels between thermodynamic baths. A complete understanding of quantum transport thus requires the ability to simulate and probe macroscopic and microscopic physics on equal footing. Using a superconducting quantum processor, we demonstrate the emergence of non-equilibrium steady quantum transport by emulating the baths with qubit ladders and realising steady particle currents between the baths. We experimentally show that the currents are independent of the microscopic details of bath initialisation, and their temporal fluctuations decrease rapidly with the size of the baths, emulating those predicted by thermodynamic baths. The above characteristics are experimental evidence of pure-state statistical mechanics and prethermalisation in non-equilibrium many-body quantum systems. Furthermore, by utilising precise controls and measurements with single-site resolution, we demonstrate the capability to tune steady currents by manipulating the macroscopic properties of the baths, including filling and spectral properties. Our investigation paves the way for a new generation of experimental exploration of non-equilibrium quantum transport in strongly correlated quantum matter. The use of quantum simulators for studying non-equilibrium quantum transport has been limited. Here the authors demonstrate the steady quantum transport between many-body qubit baths on a superconducting quantum processor, revealing insights into pure-state statistical mechanics for nonequilibrium quantum systems.