Description

Talk by A. Bertoldi (Universite Bordeaux)
Title: Atom interferometry with feedback and phase lock loopsPlace: Salon de Grados
Time: 12:00–13:00, Tuesday, 20 December, 2016

Abstract:

In atom interferometry the phase evolution of a quantum superposition state is measured with respect to a reference, e.g.
implemented with a local oscillatory signal in the case of an atom
clock and with the position of a retro-reflector for a Raman atom
gravimeter. The projection of the relative phase is measured as a
population unbalance on two energetic levels, and the phase can be recovered unambiguously only over a limited interval. Resolving phase wrapping requires to consider the effect of the measurement process on the system and specifically on its quantum coherence. Several solutions to extend the interrogation interval, hence the instrument sensitivity, have been proposed for atomic clocks [1,2], clock comparisons [3] and demonstrated in atom interferometry based inertial sensing [4]; they use two or more ensembles interrogated simultaneously to monitor the relative phase evolution at different time scales to avoid phase wraps over a longer interval. We extended the unambiguous interval to probe the phase evolution of an atomic ensemble using coherence preserving measurements and phasecorrections
[5], and demonstrate the phase lock of the clock oscillator to an
atomic superposition state [6]. We propose a protocol based on the phase lock to improve atomic clocks limited by local oscillator noise, which is the case of optical clocks, and foresee the application to other atomic interferometers such as inertial sensors.

[1] T. Rosenband and D. R. Leibrandt, "Exponential scaling of clock stability with atom number", arXiv:1303.6357 (2013).
[2] J. Borregaard and A. Sorensen, "Efficient atomic clocks operated with several atomic ensembles", Phys. Rev. Lett. 111, 090802 (2013).
[3] D. B. Hume and D. R. Leibrandt, "Probing beyond the laser
coherence time in optical clock comparisons", Phys. Rev. A 93, 032138 (2016).
[4] F. Sorrentino, et al., "Simultaneous measurement of gravity
acceleration and gravity gradient with an atom interferometer", Appl. Phys. Lett. 101, 114106 (2012).
[5] T. Vanderbruggen, et al, "Feedback control of trapped coherent atomic ensembles", Phys. Rev. Lett. 110, 210503 (2013)
[6] R. Kohlhaas, et al., "Phase locking a clock oscillator to a
coherent atomic ensemble", Phys. Rev. X 5, 021011 (2015).