Quantum Gate for Kerr Nonlinear Parametric Oscillator Using Effective Excited States

TL;DR

This paper proposes a high-fidelity, fast $R_x$ gate for Kerr nonlinear parametric oscillators by exciting higher effective states outside the qubit space, enhancing quantum gate performance for variational algorithms.

Contribution

It introduces a novel method to implement a continuous $R_x$ gate using parity-selective transitions to excite higher effective states, improving gate speed and fidelity.

Findings

Faster $R_x$ gate achieved through higher effective excited states.

Method enables continuous $R_x$ gate for KPO-based qubits.

Potential application in variational quantum algorithms.

Abstract

A Kerr nonlinear parametric oscillator (KPO) can stabilize a quantum superposition of two coherent states with opposite phases, which can be used as a qubit. In a universal gate set for quantum computation with KPOs, an $R_x$ gate, which interchanges the two coherent states, is relatively hard to perform owing to the stability of the two states. We propose a method for a high-fidelity $R_x$ gate by exciting the KPO outside the qubit space with parity-selective transitions, which can be implemented by only adding a driving field. In this method, the utilization of higher effective excited states leads to a faster $R_x$ gate, rather than states near the qubit space. The proposed method can realize a continuous $R_x$ gate and thus is expected to be useful for, e.g., recently proposed variational quantum algorithms.