Advanced Workshop on Nanomechanics September Measuring force sensitivity at the standard quantum limit

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1 Advanced Workshop on Nanomechanics 9-13 September 2013 Measuring force sensitivity at the standard quantum limit Sydney Schreppler Ultracold Atomic Physics Group UC Berkeley

2 Measuring force sensitivity at the standard quantum limit Sydney Schreppler Ultracold Atomic Physics Group, UC Berkeley PI: Dan Stamper-Kurn ICTP Frontiers of Nanomechanics, 10 September, 2013

3 From Berkeley, CA to the ICTP St. Mark s Campanile, Venice Sather Tower, Berkeley

4 From Berkeley to the ICTP San Francisco, USA Trieste, Italy James Joyce Rainer Maria Rilke Allen Ginsberg, Harold Norse, Jack Hirschman, Michael McClure & Bob Kaufman Italo Svevo

5 Summary Standard quantum limit Cold atoms for optomechanics Measuring force sensitivity The phase-space picture

6 Limits on measuring forces Accuracy of measurement limited to zero-point-fluctuations in one damping period [see Clerk et al., RMP 82, 1155 (2010)] LIGO/VIRGO Single spin NMR Rugar et al., Nature 430, 329 (2004)

7 The effort so far Westphal, et al. PRA 85, (2012) Abbott et al., NJP 11, (2009) Teufel, et al. Nature Nano 4, 820 (2009)

8 Quadrature-sensitive measurement coherent displacement incoherent zero-point fluctuations Minimum uncertainty state:

9 Standard quantum limit Sensitivity = SQL(ideal) = Zero-point motion (bath noise)

10 Standard quantum limit Sensitivity = > SQL(experiment) Zero-point motion (bath noise)

11 Cold atoms for optomechanics Decoupling from environment: atoms trapped in 845 nm standingwave optical dipole trap Dispersive measurement: probe light is detuned from atomic transition at 780 nm by Atoms collectively shift cavity resonance Mechanical ground state: shot-noise limited probe allows interrogation with no added technical noise (images + apparatus construction credit: Tom Purdy!)

12 Cold atoms for optomechanics Atom chip allows precise cloud positioning Collective atomic motion = mechanical degree of freedom )

13 Cold atoms for optomechanics Stokes Asymmetry Ponderomotive squeezing Brooks et al., Nature 488, 476 (2012) Ground-state oscillator arrays Brahms et al., PRL 108, (2012) Botter et al., PRL 110, (2013).

14 Applying a force AC trap intensity modulation shifts atoms center-ofmass

15 Measuring applied force Atom sheet = oscillator On cavity resonance, atomic motion recorded in phase of probe Measurement produces backaction force per photon

16 Measuring applied force Apply coherent classical force of fixed strength at incremental frequencies Coherent response = average Fourier transform at driven frequency Incoherent response = average noise power spectrum

17 Signal and noise spectra Normalized coherent response to constant applied force Normalized noise spectrum x 140 =

18 Measured sensitivity For typical oscillator, SQL + 1 phonon SQL Bath

19 Ideal vs. experimental SQL zpm + 1 phonon zpm + 1 phonon zpm zpm Perfect detection efficiency Actual detection efficiency

20 Phase-space response Prepare and measure sample ~1000 times at each measurement strength Incoherent response (noise) Coherent response (signal + noise) Expect diameters of ~ 1.1 zho at SQL

21 Phase-space response Imag (zho) 1 error ellipse axes (units of ) Real (zho)

22 What s next Stroboscopic QND measurements Aspelmeyer et. al, arxiv: v1 (2013)

23 Thanks to: Nicolas Spethmann Nathan Brahms Jonathan Kohler Dan Stamper-Kurn Dan Brooks Thierry Botter

24 Force calibration