title: Quantum metrology. Optically measuring force near the standard quantum limit.
abstract: The Heisenberg uncertainty principle sets a lower bound on the noise in a force measurement based on continuously detecting a mechanical oscillator's position. This bound, the standard quantum limit, can be reached when the oscillator subjected to the force is unperturbed by its environment and when measurement imprecision from photon shot noise is balanced against disturbance from measurement back-action. We applied an external force to the center-of-mass motion of an ultracold atom cloud in a high-finesse optical cavity and measured the resulting motion optically. When the driving force is resonant with the cloud's oscillation frequency, we achieve a sensitivity that is a factor of 4 above the standard quantum limit and consistent with theoretical predictions given the atoms' residual thermal disturbance and the photodetection quantum efficiency.
authors: Department of Physics, University of California, Berkeley, CA 94720, USA. sschreppler@berkeley.edu.
authors: Sydney
authors: S
authors: Schreppler
authors: Department of Physics, University of California, Berkeley, CA 94720, USA.
authors: Nicolas
authors: N
authors: Spethmann
authors: Department of Physics, University of California, Berkeley, CA 94720, USA.
authors: Nathan
authors: N
authors: Brahms
authors: Department of Physics, University of California, Berkeley, CA 94720, USA.
authors: Thierry
authors: T
authors: Botter
authors: Department of Physics, University of California, Berkeley, CA 94720, USA.
authors: Maryrose
authors: M
authors: Barrios
authors: Department of Physics, University of California, Berkeley, CA 94720, USA. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors: Dan M
authors: DM
authors: Stamper-Kurn