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arXiv · 2602.03734

Detecting quantum noise of a solid-state spin ensemble with dispersive measurement

Mikhail Mamaev·Jayameenakshi Venkatraman·Martin Koppenhöfer·Ania C. Bleszynski Jayich·Aashish A. Clerk
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Abstract

We theoretically explore protocols for measuring the spin polarization of an ensemble of solid-state spins, with precision at or below the standard quantum limit. Such measurements in the solid-state are challenging, as standard approaches based on optical fluorescence are often limited by poor readout fidelity. Indirect microwave resonator-mediated measurements provide an attractive alternative, though a full analysis of relevant sources of measurement noise is lacking. In this work we study dispersive readout of an inhomogeneously broadened spin ensemble via coupling to a driven resonator measured via homodyne detection. We derive generic analytic conditions for when the homodyne measurement can be limited by the fundamental spin-projection noise, as opposed to microwave-drive shot noise or resonator phase noise. By studying fluctuations of the measurement record in detail, we also propose an experimental protocol for directly detecting spin squeezing, i.e. a reduction of the spin ensemble's intrinsic projection noise from entanglement. Our protocol provides a method for benchmarking entangled states for quantum-enhanced metrology.

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Mikhail Mamaev, Jayameenakshi Venkatraman, Martin Koppenhöfer, Ania C. Bleszynski Jayich, Aashish A. Clerk. 2026-02-03. Detecting quantum noise of a solid-state spin ensemble with dispersive measurement. https://arxiv.org/abs/2602.03734

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