Measurement-free preparation of grid states

TL;DR

This paper introduces a measurement-free, deterministic protocol for preparing high-quality grid states in quantum computing, enhancing fault tolerance potential without the need for time-consuming measurements.

Contribution

It proposes a novel measurement-free method to generate logical grid states deterministically, improving efficiency and state quality for fault-tolerant quantum computing.

Findings

Protocol can be implemented in trapped-ion and superconducting circuits.

Generates high-quality grid states with minimal interactions.

Suitable for current noisy quantum systems.

Abstract

Quantum computing potentially offers exponential speed-ups over classical computing for certain tasks. A central, outstanding challenge to making quantum computing practical is to achieve fault tolerance, meaning that computations of any length or size can be realised in the presence of noise. The Gottesman-Kitaev-Preskill code is a promising approach towards fault-tolerant quantum computing, encoding logical qubits into grid states of harmonic oscillators. However, for the code to be fault tolerant, the quality of the grid states has to be extremely high. Approximate grid states have recently been realized experimentally, but their quality is still insufficient for fault tolerance. Current implementable protocols for generating grid states rely on measurements of ancillary qubits combined with either postselection or feed forward. Implementing such measurements take up significant time during which the states decohere, thus limiting their quality. Here we propose a measurement-free preparation protocol which deterministically prepares arbitrary logical grid states with a rectangular or hexagonal lattice. The protocol can be readily implemented in trapped-ion or superconducting-circuit platforms to generate high-quality grid states using only a few interactions, even with the noise levels found in current systems.