Quantum control of a single magnon in a macroscopic spin system

TL;DR

This paper demonstrates the first deterministic quantum control of a single magnon in a macroscopic spin system, enabling generation of non-classical states with potential quantum engineering applications.

Contribution

It introduces a method to coherently generate and manipulate non-classical magnon states in a large-scale spin system using superconducting qubits and microwave cavities.

Findings

Successful generation of single-magnon and superposition states

Wigner tomography confirms non-classical states

First deterministic control of magnons in a macroscopic system

Abstract

Non-classical quantum states are the pivotal features of a quantum system that differs from its classical counterpart. However, the generation and coherent control of quantum states in a macroscopic spin system remain an outstanding challenge. Here we experimentally demonstrate the quantum control of a single magnon in a macroscopic spin system (i.e., 1~mm-diameter yttrium-iron-garnet sphere) coupled to a superconducting qubit via a microwave cavity. By tuning the qubit frequency {\it in situ} via the Autler-Townes effect, we manipulate this single magnon to generate its non-classical quantum states, including the single-magnon state and the superposition state of a single magnon and vacuum. Moreover, we confirm the deterministic generation of these non-classical states by Wigner tomography. Our experiment offers the first reported deterministic generation of the non-classical quantum states in a macroscopic spin system and paves a way to explore its promising applications in quantum engineering.