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arXiv:1012.1574 · Physical Review A

Photon counting for Bragg spectroscopy of quantum gases

J. M. Pino, Robert J. Wild, Philip Makotyn, D. S. Jin, Eric Cornell

Published Mar 17, 2011• 26 citations
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Abstract

We demonstrate a photon-counting technique for detecting Bragg excitation of an ultracold gas of atoms. By measuring the response of the light field to the atoms, we derive a signal independent of traditional time-of-flight atom-imaging techniques. With heterodyne detection we achieve photon shot-noise limited detection of the amplification or depletion of one of the Bragg laser beams. Photon counting for Bragg spectroscopy will be useful for strongly interacting gases where atom-imaging detection fails. In addition, this technique provides the ability to resolve the evolution of excitations as a function of pulse duration.

DOI
10.1103/physreva.83.033615

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We demonstrate a photon-counting technique for detecting Bragg excitation of an ultracold gas of atoms. By measuring the response of the light field to the atoms, we derive a signal independent of traditional time-of-flight atom-imaging techniques. With heterodyne detection we achieve photon shot-noise limited detection of the amplification or depletion of one of the Bragg laser beams. Photon counting for Bragg spectroscopy will be useful for strongly interacting gases where atom-imaging detection fails. In addition, this technique provides the ability to resolve the evolution of excitations as a function of pulse duration.
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Photon counting has been widely used in weak light even to single photon detection.However,the Shot noise of photon-counting N for Poisson statistics seriously affects the sensitivity.A method using wavelength modulation spectroscopy technique to improve signal-to-noise ratio of photon-counting is presented.The light from an external cavity diode laser is wavelength modulated and then chopped to a series of laser pulses by using a acoustic-optical modulator,the counts of fluorescence photon are recorded and then converted to an analog signal.The analog signal is added to a lock-in amplifier for harmonic demodulation using lock-in method.The fluorescence spectrum is the 6S_1/2(F=4)→6P_3/2 transition of Cs D_2 line and the detected probability of photon is 35%.The experimental demonstration has achieved a 51 dB signal-to-noise improvement factor in 2f harmonic detection.The minimum detectable count here is 3×10-4 with the residual noise 7.54 μV.The results show a potential application in fluorescence detection of cold molecules or single molecule.
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We study Bragg scattering of laser light by trapped Fermi atoms having two hyperfine spin components in the unitarity-limited strongly interacting regime at zero temperature. We calculate the dynamic structure function of the superfluid trapped Fermi gas in the unitarity limit. Model calculation using local density approximation shows that, the superfluid pairing gap in the unitarity limit is detectable from the measurements of dynamic structure function by Bragg spectroscopy, while in the weak-coupling BCS limit, the gap eludes such spectroscopic detection.