Analog quantum control of magnonic cat states on-a-chip by a superconducting qubit

TL;DR

This paper proposes a method to coherently couple a superconducting qubit with magnons in a magnetic particle, enabling quantum control and the generation of entangled and cat states on a chip.

Contribution

It introduces a new on-chip coupling scheme between superconducting qubits and magnons, allowing tunable, strong interactions for quantum state engineering.

Findings

Resonant qubit-magnon exchange predicted

Nonlinear radiation-pressure interaction demonstrated

High-fidelity generation of entangled and cat states achieved

Abstract

We propose to directly and quantum-coherently couple a superconducting transmon qubit to magnons - the quanta of the collective spin excitations, in a nearby magnetic particle. The magnet's stray field couples to the qubit via a superconducting quantum interference device (SQUID). We predict a resonant qubit-magnon exchange and a nonlinear radiation-pressure interaction that are both stronger than dissipation rates and tunable by an external flux bias. We additionally demonstrate a quantum control scheme that generates qubit-magnon entanglement and magnonic Schr\"{o}dinger cat states with high fidelity.