Photon-assisted tunneling with non-classical light

TL;DR

This paper theoretically investigates how non-classical microwave states, such as squeezed and Fock states, influence a quantum electronic conductor coupled to a superconducting cavity, revealing unique quantum effects like negativity in quasi-probability distributions.

Contribution

It introduces a theoretical framework for understanding the interaction between non-classical microwaves and quantum conductors in the tunneling regime, highlighting the conductor's role as a probe of quantum microwave states.

Findings

Quantum conductors exhibit non-positive quasi-probability distributions when interacting with non-classical microwaves.

Negativity in the quasi-probability distribution affects the conductance of the quantum conductor.

The study provides insights into new physical regimes accessible with hybrid superconducting quantum systems.

Abstract

Among the most exciting recent advances in the field of superconducting quantum circuits is the ability to coherently couple microwave photons in low-loss cavities to quantum electronic conductors (e.g.~semiconductor quantum dots or carbon nanotubes). These hybrid quantum systems hold great promise for quantum information processing applications; even more strikingly, they enable exploration of completely new physical regimes. Here we study theoretically the new physics emerging when a quantum electronic conductor is exposed to non-classical microwaves (e.g.~squeezed states, Fock states). We study this interplay in the experimentally-relevant situation where a superconducting microwave cavity is coupled to a conductor in the tunneling regime. We find the quantum conductor acts as a non-trivial probe of the microwave state; in particular, the emission and absorption of photons by the conductor is characterized by a non-positive definite quasi-probability distribution. This negativity has a direct influence on the conductance of the conductor.