Implementing a Universal Gate Set on a Logical Qubit Encoded in an Oscillator

TL;DR

This paper demonstrates a high-fidelity control strategy for a logical qubit encoded in a superconducting cavity, leveraging accurate Hamiltonian knowledge to perform decoherence-limited operations in a large Hilbert space.

Contribution

The authors develop a holistic control approach exploiting Hamiltonian knowledge to manipulate oscillator-based logical qubits with high fidelity, advancing quantum information processing.

Findings

Achieved 99% fidelity in logical qubit operations

Demonstrated control of a logical qubit encoded in a superconducting cavity

Showed the effectiveness of numerical techniques for oscillator control

Abstract

A logical qubit is a two-dimensional subspace of a higher dimensional system, chosen such that it is possible to detect and correct the occurrence of certain errors. Manipulation of the encoded information generally requires arbitrary and precise control over the entire system. Whether based on multiple physical qubits or larger dimensional modes such as oscillators, the individual elements in realistic devices will always have residual interactions which must be accounted for when designing logical operations. Here we demonstrate a holistic control strategy which exploits accurate knowledge of the Hamiltonian to manipulate a coupled oscillator-transmon system. We use this approach to realize high-fidelity (99%, inferred), decoherence-limited operations on a logical qubit encoded in a superconducting cavity resonator using four-component cat states. Our results show the power of applying numerical techniques to control linear oscillators and pave the way for utilizing their large Hilbert space as a resource in quantum information processing.