Resonance fluorescence of a chiral artificial atom

TL;DR

This paper demonstrates a superconducting artificial atom with unidirectional microwave photon coupling, exhibiting non-reciprocal emission, quantum nonlinear behavior, and controllable chirality, advancing chiral quantum optics applications.

Contribution

The authors realize a superconducting artificial atom with strong unidirectional coupling and demonstrate non-reciprocal emission, quantum nonlinear effects, and controllable chirality in a scalable platform.

Findings

Achieved a forward/backward emission ratio exceeding 100.

Observed well-resolved Mollow triplets indicating quantum nonlinear behavior.

Controlled chirality for the second transition energy and implemented qubit-state-dependent non-reciprocal phase.

Abstract

We demonstrate a superconducting artificial atom with strong unidirectional coupling to a microwave photonic waveguide. Our artificial atom is realized by coupling a transmon qubit to the waveguide at two spatially separated points with time-modulated interactions. Direction-sensitive interference arising from the parametric couplings in our scheme results in a non-reciprocal response, where we measure a forward/backward ratio of spontaneous emission exceeding 100. We verify the quantum nonlinear behavior of this artificial chiral atom by measuring the resonance fluorescence spectrum under a strong resonant drive and observing well-resolved Mollow triplets. Further, we demonstrate chirality for the second transition energy of the artificial atom and control it with a pulse sequence to realize a qubit-state-dependent non-reciprocal phase on itinerant photons. Our demonstration puts forth a superconducting hardware platform for the scalable realization of several key functionalities pursued within the paradigm of chiral quantum optics, including quantum networks with all-to-all connectivity, driven-dissipative stabilization of many-body entanglement, and the generation of complex non-classical states of light.