The precise estimation of the gravitational acceleration is important for various disciplines. We consider making such an estimation using quantum optics. A Mach-Zehnder interferometer in an "optical fountain" type arrangement is considered and used to define a standard quantum limit for estimating the gravitational acceleration. We use an approach based on quantum field theory on a curved, Schwarzschild metric background to calculate the coupling between the gravitational field and the optical signal. The analysis is extended to include the injection of a squeezed vacuum to the Mach-Zehnder arrangement and also to consider an active, two-mode SU(1,1) interferometer in a similar arrangement. When detection loss is larger than 8%, the SU(1,1) interferometer shows an advantage over the MZ interferometer with single-mode squeezing input. The proposed system is based on current technology and could be used to examine the intersection of quantum theory and general relativity as well as for possible applications.
We investigate polarization spectroscopy of an excited state transition in room-temperature rubidium vapor. By applying a circularly polarized coupling beam, resonant with the 52S1/2 → 52P3/2 transition, we induce anisotropy in the atomic medium that is then probed by scanning a probe beam across the 52P3/2 → 62S1/2 transition. By performing polarimetry on the probe beam, a dispersive spectral feature is observed. We characterize the excited-state polarization spectrum as a function of coupling intensity for both isotopes and find that at high intensities, Autler-Townes splitting results in a sub-feature, which theoretical modelling shows is enhanced by Doppler averaging. This spectroscopic technique produces a narrow dispersive signal which is ideal for laser frequency stabilization to excited-state transitions.
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