Abstract
In cavity-based axion dark matter detectors, quantum noise remains a primary barrier to achieving the scan rate necessary for a comprehensive search of axion parameter space. Here, we introduce a method of scan rate enhancement in which an axion-sensitive cavity is coupled to an auxiliary resonant circuit through simultaneous two-mode squeezing (entangling) and state-swapping interactions. We show analytically that when combined, these interactions can amplify an axion signal before it becomes polluted by vacuum noise introduced by measurement. This internal amplification yields a wider bandwidth of axion sensitivity, increasing the rate at which the detector can search through frequency space. With interaction rates predicted by circuit simulations of this system, we show that this technique can increase the scan rate up to 15-fold relative to the scan rate of a detector limited by vacuum noise.Received 9 July 2021Accepted 22 October 2021Corrected 5 January 2022DOI:https://doi.org/10.1103/PRXQuantum.2.040350Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasOptical & microwave phenomenaQuantum metrologySuperconducting quantum opticsPhysical SystemsAxionsQuantum cavitiesAtomic, Molecular & OpticalParticles & Fields
Highlights
Several recent experiments in fundamental physics, including searches for axion dark matter and gravitational waves, have reduced noise below the level of vacuum fluctuations [1,2,3]
We have introduced a system capable of amplifying an axion signal through simultaneous two-mode squeezing and state-swapping interactions, and shown that this system can significantly widen the visibility bandwidth of a haloscope, yielding up to a 15-fold enhancement over the quantum-limited scan rate
We have introduced methods for mitigating problems caused by the periodic standing wave modes of a transmission line required to spatially separate the auxiliary readout resonator from the high magnetic field surrounding the axion-sensitive cavity
Summary
Several recent experiments in fundamental physics, including searches for axion dark matter and gravitational waves, have reduced noise below the level of vacuum fluctuations [1,2,3]. A second source of noise is introduced by the act of measurement itself This noise, comprising thermal and vacuum fluctuations arising from loss external to the cavity, dominates off resonance and leads to a finite visibility bandwidth [15]. This method involves using simultaneous two-mode squeezing (entangling) and state-swapping interactions to realize a quantum nondemolition interaction between the cavity mode and an auxiliary resonant mode of a spatially separated readout circuit. V, we calculate the scan rate enhancement achievable with this system
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