Robust preparation of Wigner-negative states with optimized SNAP-displacement sequences

TL;DR

This paper demonstrates the experimental generation of various Wigner-negative quantum states in microwave cavities using optimized SNAP-displacement sequences, achieving high fidelity and robustness to system fluctuations.

Contribution

It introduces a two-step optimization method for preparing non-classical states in a harmonic oscillator using SNAP and displacement gates, including the first experimental realization of cubic phase states.

Findings

Successful high-fidelity creation of Schrödinger-cat, binomial, GKP, and cubic phase states.

The state preparation method is robust against fluctuations in system parameters.

Optimization improves the fidelity and stability of non-classical state generation.

Abstract

Hosting non-classical states of light in three-dimensional microwave cavities has emerged as a promising paradigm for continuous-variable quantum information processing. Here we experimentally demonstrate high-fidelity generation of a range of Wigner-negative states useful for quantum computation, such as Schr\"{o}dinger-cat states, binomial states, Gottesman-Kitaev-Preskill (GKP) states, as well as cubic phase states. The latter states have been long sought after in quantum optics and were never achieved experimentally before. To do so, we use a sequence of interleaved selective number-dependent arbitrary phase (SNAP) gates and displacements. We optimize the state preparation in two steps. First we use a gradient-descent algorithm to optimize the parameters of the SNAP and displacement gates. Then we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly non-classical states in a harmonic oscillator is robust to fluctuations of the system parameters such as the qubit frequency and the dispersive shift.