Nonequilibrium Quantum Critical Steady State: Transport Through a Dissipative Resonant Level

TL;DR

This paper investigates the nonequilibrium steady-state current near a quantum critical point in a dissipative quantum dot system, combining analytical theory and experimental measurements with excellent agreement.

Contribution

It provides the first combined analytical and experimental study of nonequilibrium transport at a quantum critical point in a dissipative resonant level system.

Findings

Analytical calculation matches experimental data without fitting parameters.

Identifies a two-channel Kondo-like quantum critical point in the system.

Demonstrates the system's suitability for studying nonequilibrium quantum phenomena.

Abstract

Nonequilibrium properties of correlated quantum matter are being intensively investigated because of the rich interplay between external driving and the many-body correlations. Of particular interest is the nonequilibrium behavior near a quantum critical point (QCP), where the system is delicately balanced between different ground states. We present both an analytical calculation of the nonequilibrium steady-state current in a critical system and experimental results to which the theory is compared. The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an ohmic dissipative environment. A two channel Kondo-like QCP occurs when the level is on resonance and symmetrically coupled to the leads, conditions achieved by fine-tuning using electrostatic gates. We calculate and measure the nonlinear current as a function of bias ($I$-$V$ curve) at the critical values of the gate voltages corresponding to the QCP. The quantitative agreement between the experimental data and the theory, with no fitting parameter, is excellent. As our system is fully accessible to both theory and experiment, it provides an ideal setting for addressing nonequilibrium phenomena in correlated quantum matter.