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  • Open Access

Ultralow-Power Microwave Frequency Comb at a Bistable Phase Transition

Hanfeng Wang1,*, Kurt Jacobs2,3, Dirk R. Englund1, and Matthew E. Trusheim1,2,†

  • *Contact author: hanfengw@mit.edu
  • †Contact author: matthew.e.trusheim.civ@army.mil
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Phys. Rev. X 16, 021005 – Published 6 April, 2026

DOI: https://doi.org/10.1103/59xl-zyxp

Abstract

Nonlinear phenomena underpin a broad array of technologies, from electronic frequency mixers and harmonic generation to parametric amplification and optical frequency doubling. Conventional schemes for generating microwave frequency combs are constrained by intrinsic material or junction properties that require high driving powers. Here, we overcome these limitations via phase-transition physics. We show that a hybrid quantum system—composed of a solid-state spin ensemble and a nonlinear oscillator—exhibits a distinct bistable phase transition point (BP) where system response becomes both highly enhanced and nonlinear. The nonlinearity around the BP is higher order than other phase transitions, such as exceptional points, critically producing high-order frequency response which enhances nonlinear processes. Approaching the BP, we demonstrate a frequency comb with a record number of teeth at unprecedentedly low driving powers, surpassing previous results using magnonic systems and traditional diode-based approaches. These findings highlight the potential of hybrid quantum systems in advancing high-performance frequency manipulation.

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Physics Subject Headings (PhySH)

Popular Summary

Generating strong nonlinear behavior for applications like frequency combs traditionally relies on intrinsic material properties that require relatively high driving powers. We demonstrate a low-power approach in a hybrid quantum system by coupling an ensemble of nitrogen-vacancy centers in diamond to a microwave oscillator near a bistable phase transition point. We observe that operating at this specific point yields an enhanced higher-order nonlinear response. This behavior allows us to generate a microwave frequency comb with 193 distinct spectral teeth using only −16.6  dBm of driving power, significantly lower than existing conventional platforms. Our findings provide a pathway for advancing low-power and high-precision technologies in quantum sensing, communications, and metrology.

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Phys. Rev. X 16, 021005– Published 6 April, 2026
  • Received 11 August 2025
  • Accepted 29 January 2026
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