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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Laser-cooling in noisy quadrature of squeezed vacuum for cesium fountain clock

G. M. Saxena, Ashish Agarwal

Published Jul 8, 2004• 0 citations

Abstract

In this paper we report that the noisy quadrature, a undesirable feature of the squeezed light, could be effectively used in realizing higher cooling force in the Cs fountain clock. We know that the laser cooling is basically the result of the combination of undesirable phenomena like light shift, Doppler shift and polarization gradient. We establish in this paper that the noisy quadrature, a unwelcome feature of the squeezed light is useful in achieving larger cooling force. When the atoms interact with the squeezed vacuum, they decay into two quadratures which respectively have quantum noise below and above the normal vacuum fluctuations. The noisy quadrature corresponds to the faster decay rate. On subjecting the Cs atoms to the noisy quadrature of the squeezed vacuum, superimposed with the squeezed coherent light, the cooling force is increased. The use of the noisy quadrature of the squeezed vacuum for obtaining larger cooling force and the temperatures much below the Doppler limit, without resorting to large detuning of the driving field, is a novel idea discussed in this paper. We report that the S/N of the clock signal may also be improved with the squeezed light.

DOI: 10.1109/freq.2003.1275075

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In this paper we report that the noisy quadrature, a undesirable feature of the squeezed light, could be effectively used in realizing higher cooling force in the Cs fountain clock. We know that the laser cooling is basically the result of the combination of undesirable phenomena like light shift, Doppler shift and polarization gradient. We establish in this paper that the noisy quadrature, a unwelcome feature of the squeezed light is useful in achieving larger cooling force. When the atoms interact with the squeezed vacuum, they decay into two quadratures which respectively have quantum noise below and above the normal vacuum fluctuations. The noisy quadrature corresponds to the faster decay rate. On subjecting the Cs atoms to the noisy quadrature of the squeezed vacuum, superimposed with the squeezed coherent light, the cooling force is increased. The use of the noisy quadrature of the squeezed vacuum for obtaining larger cooling force and the temperatures much below the Doppler limit, without resorting to large detuning of the driving field, is a novel idea discussed in this paper. We report that the S/N of the clock signal may also be improved with the squeezed light.

The process of laser cooling in a quasi resonant standing laser wave is one of the principal technics of laser cooling of atoms. Recent advances in this field include breaking both the "Doppler and the recoil limits". On another front modification of the quantum statistical properties of the "vacuum" fluctuations by squeezing has been achieved in the laboratory. It is, therefore, interesting to find what is the nature of the modification of the laser cooling process when the atoms are also embedded in squeezed vacuum. Such a state can be produced in principle by a degenerate parametric amplifier whose input are vacuum fluctuations. It is shown that due to the modified decay rates of an atom which is embedded in such a state, profound modification of the cooling processes in a standing wave is achieved . Among the important results obtained is the change of sign of the stimulated force from a heating force in normal vacuum to a cooling force in squeezed vacuum. This phenomenon can result in cooling forces more than two orders of magnitude larger than the maximum force in normal vacuum. In this talk the method for calculating the force in squeezed vacuum will be given. The modified force will be compared to the force in normal vacuum and finally the practical implications of these results for laser cooling will be discussed.

We investigate theoretically and experimentally a nondestructive interferometric measurement of the state population of an ensemble of laser-cooled and trapped atoms. This study is a step toward generation of (pseudo)spin squeezing of cold atoms targeted at the improvement of the cesium clock performance beyond the limit set by the quantum projection noise of atoms. We calculate the phase shift and the quantum noise of a near-resonant optical probe pulse propagating through a cloud of cold

^{133}\mathrm{Cs}

atoms. We analyze the figure of merit for a quantum nondemolition (QND) measurement of the collective pseudospin and show that it can be expressed simply as a product of the ensemble optical density and the pulse-integrated rate of the spontaneous emission caused by the off-resonant probe light. Based on this, we propose a protocol for the sequence of operations required to generate and utilize spin squeezing for the improved atomic clock performance via a QND measurement on the probe light. In the experimental part we demonstrate that the interferometric measurement of the atomic population can reach a sensitivity of the order of

\sqrt{{N}_{\mathrm{at}}}

in a cloud of

{N}_{\mathrm{at}}

cold atoms, which is an important benchmark toward the experimental realization of the theoretically analyzed protocol.