Overcoming the Standard Quantum Limit in Gravitational Wave Detectors Using Spin Systems with a Negative Effective Mass

F. Ya. Khalili and E. S. Polzik
Phys. Rev. Lett. 121, 031101 – Published 16 July 2018
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Abstract

Quantum backaction (QBA) of a measurement limits the precision of observation of the motion of a free mass. This profound effect, dubbed the “Heisenberg microscope” in the early days of quantum mechanics, leads to the standard quantum limit (SQL) stemming from the balance between the measurement sensitivity and the QBA. We consider the measurement of motion of a free mass performed in a quantum reference frame with an effective negative mass which is not limited by QBA. As a result, the disturbance on the motion of a free mass can be measured beyond the SQL. QBA-limited detection of motion for a free mass is extremely challenging, but there are devices where this effect is expected to play an essential role, namely, gravitational wave detectors (GWDs) such as LIGO and Virgo. Recent reports on the observations of gravitational waves have opened new horizons in cosmology and astrophysics. We present a general idea and a detailed numerical analysis for QBA-evading measurement of the gravitational wave effect on the GWD mirrors, which can be considered free masses under relevant conditions. The measurement is performed by two entangled beams of light, probing the GWD and an auxiliary atomic spin ensemble, respectively. The latter plays the role of a free negative mass. We show that under realistic conditions the sensitivity of the GWD in m/Hz can be increased by 6 dB over the entire frequency band of interest.

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  • Received 29 October 2017
  • Revised 11 May 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.031101

© 2018 American Physical Society

Physics Subject Headings (PhySH)

General Physics

Authors & Affiliations

F. Ya. Khalili*

  • Faculty of Physics, M.V. Lomonosov Moscow State University, 119991 Moscow, Russia and Russian Quantum Center, Skolkovo 143025, Russia

E. S. Polzik

  • Niels Bohr Institute, University of Copenhagen, Copenhagen 2100, Denmark

  • *khalili@phys.msu.ru
  • polzik@nbi.ku.dk

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Issue

Vol. 121, Iss. 3 — 20 July 2018

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