Abstract
Many experiments that interrogate fundamental theories require detectors whose sensitivities are limited by the laws of quantum mechanics. In cavity-based searches for axionic dark matter, vacuum fluctuations in the two quadratures of the cavity electromagnetic field limit the sensitivity to an axion-induced field. In an apparatus designed to partially mimic existing axion detectors, we demonstrate experimentally that such quantum limits can be overcome through the use of squeezed states. By preparing a microwave cavity in a squeezed state and measuring just the squeezed quadrature, we enhance the spectral scan rate by a factor of . This enhancement is in excellent quantitative agreement with a theoretical model accounting for both imperfect squeezing and measurement.
- Received 17 September 2018
- Revised 25 January 2019
DOI:https://doi.org/10.1103/PhysRevX.9.021023
Published 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 Society
Physics Subject Headings (PhySH)
Erratum
Erratum: Squeezed Vacuum Used to Accelerate the Search for a Weak Classical Signal [Phys. Rev. X 9, 021023 (2019)]
M. Malnou, D. A. Palken, B. M. Brubaker, Leila R. Vale, Gene C. Hilton, and K. W. Lehnert
Phys. Rev. X 10, 039902 (2020)
Popular Summary
Measurements of a force whose coupling to a detector is extremely feeble can be obscured by quantum-mechanical noise. Such is the case when searching for axionic dark matter, a hypothetical microwave signal of unknown frequency, where fluctuations arising from the Heisenberg uncertainty principle necessitate prohibitively long measurement times. Here, we exploit microwave squeezed states of the electromagnetic field to circumvent the quantum limit, thereby accelerating the search for a small classical signal.
A microwave cavity can be used as an axion detector: When tuned to resonance with the axion field, the cavity state may be displaced by an amount that is small compared to the scale of quantum fluctuations. Introducing a squeezed state receiver apparatus, we demonstrate both theoretically and experimentally the squeezed state receiver’s ability to achieve a favorable trade-off between the detector’s bandwidth and its peak sensitivity, enabling a faster signal search. By injecting a synthetic tone, shaped to mimic a real axion signal, into the cavity at an unknown frequency, we demonstrate an enhancement in the detection rate by a factor of 2.
Our technique is straightforwardly applicable to existing axion detectors and will permit still greater scan rates as microwave-component losses are further reduced.
