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arXiv:1204.5223 · Review of Scientific Instruments

Sensitivity test of a blue-detuned dipole trap designed for parity non-conservation measurements in Fr

D. Sheng, J. Zhang, Luis A. Orozco

Published Apr 1, 2012• 16 citations
arXivHTMLPDF

Abstract

A dynamic blue-detuned optical dipole trap with stable (87)Rb atoms produces a differential ac Stark shift of 18 Hz in the ground state hyperfine transition, and it preserves the ground state hyperfine superpositions for a long coherence time of 180 ms. The trapped atoms undergoing microwave Rabi oscillations are sensitive to a small signal, artificially generated with a second microwave source, phase locked to the first allowing a simple and effective method for determining signal-to-noise ratio limits through interference techniques. This provides an excellent means of calibrating sensitivity in experiments such as our ongoing Fr parity non-conservation measurement.

DOI
10.1063/1.3701714

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arXiv:1311.1290•Physical Review Letters•Dec 11, 2013•34 citations
A dynamic blue-detuned optical dipole trap with stable (87)Rb atoms produces a differential ac Stark shift of 18 Hz in the ground state hyperfine transition, and it preserves the ground state hyperfine superpositions for a long coherence time of 180 ms. The trapped atoms undergoing microwave Rabi oscillations are sensitive to a small signal, artificially generated with a second microwave source, phase locked to the first allowing a simple and effective method for determining signal-to-noise ratio limits through interference techniques. This provides an excellent means of calibrating sensitivity in experiments such as our ongoing Fr parity non-conservation measurement.
Blue-detuned dipole traps and their ability to preserve atomic coherences are interesting for precision measurement applications. In this paper, we present experimental studies on the differential ac Stark shift of the ground-state hyperfine splitting in 87{}^{87}87Rb atoms confined in a dynamic blue-detuned dipole trap. We systematically study the power and detuning effects on the Rabi resonance frequency (differential ac Stark shift) and its linewidth (coherence) and find that their performance is compatible with future parity violation experiments in Fr.
Summary form only given. We have constructed a new apparatus for producing and on-line trapping of francium for parity non-conservation experiments. At present, we have produced and delivered 15 /spl times/ 10/sup 6/ Fr/sec to the trapping area with better than 90% efficiency. The electrostatic optics of our beamline ensure mass independent transport of all francium isotopes and even other alkalis, such as rubidium, which we use for testing most of our apparatus. After accumulation in this first MOT, we transfer the atoms to a second MOT in a separate vacuum chamber one meter below, where they are transferred to a far off-resonance optical dipole trap for PNC experiments. At present, we are constructing the apparatus for a measurement of the PNC anapole moment by probing the microwave E1 transition between the ground state hyperfine levels of francium.
Sodium atoms have been stored in a blue-detuned dipole trap based on sheets of argon ion laser light which support against gravity. In this trap, the atoms spend most of their time in free fall, resulting in a large reduction in the perturbation of the atomic levels due to the trapping potential. This reduction enabled us to probe the ground state hyperfine splitting with a measurement time of 4 s, yielding a linewidth of 0.125 Hz and a Ramsey fringe contrast of 43%. The coherence time was $\ensuremath{\sim}$300 times longer than achieved in a red-detuned Nd:YAG laser dipole trap with comparable depth.
Polar molecules offer a new platform for quantum simulation of systems with long-range interactions, based on the electrostatic interaction between their electric dipole moments. Here, we report the development of coherent quantum state control using microwave fields in 40 Ca 19 F and 87 Rb 133 Cs molecules, a crucial ingredient for many quantum simulation applications. We perform Ramsey interferometry measurements with fringe spacings of ∼1 kHz and investigate the dephasing time of a superposition of N = 0 and N = 1 rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped 40 Ca 19 F we use a magnetically insensitive transition and observe a coherence time of 0.61(3) ms. For optically trapped 87 Rb 133 Cs we exploit an avoided crossing in the AC Stark shifts and observe a maximum coherence time of 0.75(6) ms.
We demonstrate the cancellation of the differential ac Stark shift of the microwave hyperfine clock transition in trapped 87 Rb atoms. Recent progress in metrology exploits so-called “magic wavelengths,” whereby an atomic ensemble can be trapped with laser light whose wavelength is chosen so that both levels of an optical atomic transition experience identical ac Stark shifts. Similar magic-wavelength techniques are not possible for the microwave hyperfine transitions in the alkalis, due to their simple electronic structure. We show, however, that ac Stark shift cancellation is indeed achievable for certain values of wavelength, polarization, and magnetic field. The cancellation comes at the expense of a small magnetic-field sensitivity. The technique demonstrated here has implications for experiments involving the precise control of optically-trapped neutral atoms.
We demonstrate that the differential ac-Stark shift of a Zeeman-sensitive ground hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the $|2{S}_{1/2},F=2,{m}_{F}=\ensuremath{-}2⟩$ to the $|2{S}_{1/2},F=1,{m}_{F}=\ensuremath{-}1⟩$ state of 7Li^{7}\mathrm{Li}7Li to observe $0.59\ifmmode\pm\else\textpm\fi{}0.02\text{ }\text{ }\mathrm{Hz}$ linewidth with interrogation time of 2 s and $0.82\ifmmode\pm\else\textpm\fi{}0.06\text{ }\text{ }\mathrm{s}$ coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed.