Protocol for generating an arbitrary quantum state of the magnetization in cavity magnonics

TL;DR

This paper presents a protocol for generating arbitrary quantum states of magnetization in cavity magnonics, utilizing superconducting transmons and microwave cavities, with strategies to mitigate decoherence and leakage for high-fidelity state preparation.

Contribution

The paper introduces a novel protocol combining transmon excitation and microwave transfer to produce arbitrary magnon states, including leakage correction techniques for improved fidelity.

Findings

States with up to ~9 magnons achieved with >75% fidelity

Protocol operates faster than magnon lifetime to prevent decay

Leakage correction improves state fidelity

Abstract

We propose and numerically evaluate a protocol to generate an arbitrary quantum state of the magnetization in a magnet. The protocol involves repeatedly exciting a frequency-tunable superconducting transmon and transferring the excitations to the magnet via a microwave cavity. To avoid decay, the protocol must be much shorter than magnon lifetime. Speeding up the protocol by simply shortening the pulses leads to non-resonant leakage of excitations to higher levels of the transmon accompanied by higher decoherence. We discuss how to correct for such leakages by applying counter pulses to de-excite these higher levels. In our protocol, states with a maximum magnon occupation of up to $\sim9$ and average magnon number up to $\sim4$ can be generated with fidelity $>0.75$.