Probing an electron spin ensemble with squeezed microwave signals

TL;DR

This paper demonstrates the interaction of squeezed microwave signals with an electron spin ensemble, showing potential for quantum memory applications by achieving a 61% transfer efficiency.

Contribution

It experimentally investigates the use of spin ensembles as quantum memories for GHz signals using squeezed microwaves, with a detailed theoretical model.

Findings

Achieved up to 5dB squeezing of microwave states.

Observed 61% transfer efficiency between microwaves and spins.

Provided a steady-state quantum input-output model for system design.

Abstract

The efficient transfer of quantum states into a long-lived storage unit such as solid-state spin ensembles is widely recognized as a critical challenge with significant implications for quantum communication, sensing and computing applications. Here, we experimentally investigate the interaction of propagating squeezed microwaves with an electron spin resonance transition in order to evaluate the use of spin ensembles as quantum memories for GHz signals. We generate continuous variable microwave states with a squeezing of up to 5dB below the vacuum level and let this signal interrogate a spin ensemble, which is inductively coupled to a lumped element superconducting microwave resonator with a cooperativity of C=0.3. Analyzing this signal using Wigner tomography, we observe a transfer efficiency of around 61% between the squeezed microwaves and the spin excitation. We successfully model our experimental results with a dedicated steady-state model based on the quantum input-output formalism and provide guidance for design parameters required to enable spin-based quantum memories.