Interferometer readout noise below the standard quantum limit of a membrane

T. Westphal*, D. Friedrich, H. Kaufer, K. Yamamoto, S. Gossler, H.M. Uller-Ebhardt, S.L. Danilishin, F.Y. Khalili, K. Danzmann, R. Schnabel

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Here we report on the realization of a Michelson-Sagnac interferometer whose purpose is the precise characterization of the motion of, i.e., membranes showing significant light transmission. Our interferometer has a readout noise spectral density (imprecision) of 3 x 10(-16) m/root Hz at frequencies around the fundamental resonance of a SiNx membrane at about 100 kHz, without using optical cavities. The readout noise demonstrated is more than 16 dB below the peak value of the membrane''s standard quantum limit (SQL). This margin is significantly bigger than those of previous works with nanowires [Teufel et al., Nature Nano. 4, 820 (2009); Anetsberger et al., Nature Phys. 5, 909 (2009)]. We discuss the meaning of the SQL for force measurements and its relation to the readout performance and emphasize that neither our nor previous experiments achieved a total noise spectral density as low as the SQL due to thermal noise.
Original languageEnglish
Article number063806
Number of pages5
JournalPhysical Review A
Issue number6
Publication statusPublished - 6 Jun 2012
Externally publishedYes




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