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Published January 15, 2002 | Accepted Version + Published
Journal Article Open

Conversion of conventional gravitational-wave interferometers into quantum nondemolition interferometers by modifying their input and/or output optics


The LIGO-II gravitational-wave interferometers (ca. 2006–2008) are designed to have sensitivities near the standard quantum limit (SQL) in the vicinity of 100 Hz. This paper describes and analyzes possible designs for subsequent LIGO-III interferometers that can beat the SQL. These designs are identical to a conventional broad band interferometer (without signal recycling), except for new input and/or output optics. Three designs are analyzed: (i) a squeezed-input interferometer (conceived by Unruh based on earlier work of Caves) in which squeezed vacuum with frequency-dependent (FD) squeeze angle is injected into the interferometer's dark port; (ii) a variational-output interferometer (conceived in a different form by Vyatchanin, Matsko and Zubova), in which homodyne detection with FD homodyne phase is performed on the output light; and (iii) a squeezed-variational interferometer with squeezed input and FD-homodyne output. It is shown that the FD squeezed-input light can be produced by sending ordinary squeezed light through two successive Fabry-Pérot filter cavities before injection into the interferometer, and FD-homodyne detection can be achieved by sending the output light through two filter cavities before ordinary homodyne detection. With anticipated technology (power squeeze factor e-2R=0.1 for input squeezed vacuum and net fractional loss of signal power in arm cavities and output optical train ε*=0.01) and using an input laser power Io in units of that required to reach the SQL (the planned LIGO-II power, ISQL), the three types of interferometer could beat the amplitude SQL at 100 Hz by the following amounts μ≡sqrt[Sh]/sqrt[ShSQL] and with the following corresponding increase V=1/μ3 in the volume of the universe that can be searched for a given noncosmological source: Squeezed input —μ≃sqrt[e-2R]≃0.3 and V≃1/0.33≃30 using Io/ISQL=1. Variational-output—μ≃ε*1/4≃0.3 and V≃30 but only if the optics can handle a ten times larger power: Io/ISQL≃1/sqrt[ε*]=10. Squeezed varational —μ=1.3(e-2Rε*)1/4≃0.24 and V≃80 using Io/ISQL=1; and μ≃(e-2Rε*)1/4≃0.18 and V≃180 using Io/ISQL=sqrt[e-2R/ε*]≃3.2.

Additional Information

© 2001 The American Physical Society. Received 11 August 2000; published 26 December 2001. For helpful discussions or email, one or more of the authors thank Vladimir Braginsky, Alessandra Buonanno, Carlton Caves, Yanbei Chen, Eanna Flanagan, Mikhail Gorodetsky, Farid Khalili, Patricia Purdue, Stan Whitcomb, Bill Unruh, and members of the Caltech QND Reading Group — most especially Constantin Brif, Bill Kells and John Preskill. We also thank Buonanno and Chen for pointing out several errors in the manuscript. This paper was supported in part by NSF grants PHY-9503642 (S.P.V.), PHY-9722674 (H.J.K.), PHY-9732445 (A.B.M.), PHY-9800097 (S.P.V.) and PHY-9900776 (K.S.T. and Y.L.), by the Office of Naval Research (H.J.K. and A.B.M.), by DARPA via the QUIC (Quantum Information and Computing) program administered by ARO (H.J.K.), by the Institute for Quantum Information (IQI) funded by the NSF-ITR program (H.I.K.), by the Caltech MURI on quantum networks administered by the Army Research Office (H.J.K.), and by the Russian Foundation for Fundamental Research grants No. 96-02-16319a and No. 97-02-0421g (S.P.V.).

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Accepted Version - 0008026.pdf


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