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

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 similar to 9 and average magnon number up to similar to 4 can be generated with fidelity >0.75.

Automated summary

We propose a protocol to generate arbitrary magnetization quantum states in a magnet and numerically evaluate its effectiveness. The protocol involves exciting a frequency-tunable superconducting transmon and transferring the excitations to the magnet, with counter pulses applied to correct for leakage. The protocol allows for the generation of high fidelity magnon states.