Propagating Wigner-Negative States Generated from the Steady-State Emission of a Superconducting Qubit

TL;DR

This paper reports the experimental generation and characterization of steady-state Wigner-negative quantum states emitted by a superconducting qubit, demonstrating high fidelity and potential for quantum information applications.

Contribution

It introduces a method to generate and verify propagating Wigner-negative states from a superconducting qubit in steady state, with high fidelity and practical relevance.

Findings

Achieved Wigner logarithmic negativity > 0.08

Fidelity with theoretical predictions up to 99%

Demonstrated steady-state nonclassical state generation

Abstract

We experimentally demonstrate the steady-state generation of propagating Wigner-negative states from a continuously driven superconducting qubit. We reconstruct the Wigner function of the radiation emitted into propagating modes defined by their temporal envelopes, using digital filtering. For an optimized temporal filter, we observe a large Wigner logarithmic negativity, in excess of 0.08, in agreement with theory. The fidelity between the theoretical predictions and the states generated experimentally is up to 99%, reaching state-of-the-art realizations in the microwave frequency domain. Our results provide a new way to generate and control nonclassical states, and may enable promising applications such as quantum networks and quantum computation based on waveguide quantum electrodynamics.