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Quantum Electronics and Laser Science Conference

High sensitivity two-photon spectroscopy of cold atoms in a dark optical trap, using an electron shelving scheme

Lev Khaykovich, Nir Friedman, Roee Ozeri, D. Fathi, Nir Davidson

Published May 12, 2000• 0 citations
OpenAlex

Abstract

Summary form only given. Utilizing cold and trapped atoms for precision spectroscopy of weak atomic transitions has two important advantages: the suppression of Doppler and time-of-flight broadenings and a combination of long interaction times, weak perturbations and tight confinement, which can be obtained using dark optical traps. We present a new and extremely sensitive method for measuring weak transitions with cold atoms in a dark optical trap, using electron shelving spectroscopy. Our scheme is based on a /spl Lambda/ system. Atoms with two ground states (for example, two hyperfine levels) are stored in the trap in a level that is coupled to the upper (excited) state, by an extremely weak transition. Atoms that undergo the weak transition may be shelved by a spontaneous Raman transition on the second ground level, which is uncoupled to the excited level by the measured photons. Finally, the detection scheme benefits from the multiply excited fluorescence of a strong closed transition from the uncoupled ground-state, that utilizes quantum amplification due to the electron shelving technique. We realized this scheme on a 5S/sub 1/2//spl rarr/5D/sub 5/2/ two-photon transition in cold and optically trapped /sup 85/Rb atoms.

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"The work presented in this thesis is concerned with the manipulation of laser- cooled rubidium atoms and the detection of small numbers of cold atoms using very sensitive light detectors. Laser-cooled atoms are atoms that have been slowed to very low velocities, corresponding to temperatures of the order of 100 //K, and they can be trapped in magnetic and/or optical traps. The advantage of using cold atoms for experiments in atomic and quantum physics stems from the fact that these atoms are effectively confined within a region of space and this provides longer interaction and observation times compared to atoms at room temperature. Hence, it is possible to explore and observe a number of effects that would otherwise be extremely challenging. The achievement of laser cooling and trapping of neutral atoms was a major breakthrough in the mid 80’s and has resulted in significant advances being made in modern spectroscopy, the realisation of Bose-Einstein condensation, atomic clocks, and quantum information technologies amongst others. In particular, the work focuses on two theoretical proposals for developing microtraps for cold rubidium atoms involving (i) ultrathin optical fibres and (ii) wavelength sized apertures in thin films. In addition, a number of experimental techniques are explored with emphasis on the detection of small numbers of atoms near ultrathin optical fibres using both avalanche photodiodes and single photon detectors. A study on the interactions between atoms and photons is crucial for a full understanding of quantum mechanical processes at the few atom scale and detection schemes sensitive to very low levels of fluorescence from the laser-cooled atoms are vital for attaining this goal. Finally, an experimental study on the design and fabrication of arrays of silica microdisks, that could be used for facilitating interactions between cold atoms and photons, is presented."

Sword•Jan 1, 2008•0 citations
Summary form only given. Utilizing cold and trapped atoms for precision spectroscopy of weak atomic transitions has two important advantages: the suppression of Doppler and time-of-flight broadenings and a combination of long interaction times, weak perturbations and tight confinement, which can be obtained using dark optical traps. We present a new and extremely sensitive method for measuring weak transitions with cold atoms in a dark optical trap, using electron shelving spectroscopy. Our scheme is based on a /spl Lambda/ system. Atoms with two ground states (for example, two hyperfine levels) are stored in the trap in a level that is coupled to the upper (excited) state, by an extremely weak transition. Atoms that undergo the weak transition may be shelved by a spontaneous Raman transition on the second ground level, which is uncoupled to the excited level by the measured photons. Finally, the detection scheme benefits from the multiply excited fluorescence of a strong closed transition from the uncoupled ground-state, that utilizes quantum amplification due to the electron shelving technique. We realized this scheme on a 5S/sub 1/2//spl rarr/5D/sub 5/2/ two-photon transition in cold and optically trapped /sup 85/Rb atoms.
We propose a new spectroscopic method for measuring weak transitions in cold and trapped atoms, which exploits the long spin relaxation times and tight spatial confinement offered by dark optical traps to achieve extremely high sensitivity. We demonstrate our scheme by measuring a 5 S 1/2 → 5 D 5/2 two-photon transition in cold Rb atoms trapped in a new single-beam dark optical trap, using an extremely weak probe laser power of 25 μW. We were able to measure transitions with as small excitation rate as < 0.1 s −1 , using 10 7 fold quantum amplification of the transition rate due to spin shelving and normalized detection with a strong cycling transition.
Summary form only given. A Doppler free measurement of the hyperfine structure splitting (HFS) of 5S/sub 1/2/ level is performed using trapped sodium atoms. We employed two techniques: 1) trap loss enhancement, which consists in the observation of the trapped atom fluorescence when an extra loss channel is created by single photon ionization of the 5S state. This method was not very precise because the lack of absolute reference. 2) Photoionization out of 5S/sub 1/2/ after a two photon excitation from the 3S/sub 1/2/ state.
The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at {approximately}400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise ({le}1 ppm) value for the dissociation energy of the X {Sigma}{sub g}{sub +} ground state of the Na{sub 2} molecule.
"The work presented in this thesis is concerned with the manipulation of laser- cooled rubidium atoms and the detection of small numbers of cold atoms using very sensitive light detectors. Laser-cooled atoms are atoms that have been slowed to very low velocities, corresponding to temperatures of the order of 100 //K, and they can be trapped in magnetic and/or optical traps. The advantage of using cold atoms for experiments in atomic and quantum physics stems from the fact that these atoms are effectively confined within a region of space and this provides longer interaction and observation times compared to atoms at room temperature. Hence, it is possible to explore and observe a number of effects that would otherwise be extremely challenging. The achievement of laser cooling and trapping of neutral atoms was a major breakthrough in the mid 80’s and has resulted in significant advances being made in modern spectroscopy, the realisation of Bose-Einstein condensation, atomic clocks, and quantum information technologies amongst others. In particular, the work focuses on two theoretical proposals for developing microtraps for cold rubidium atoms involving (i) ultrathin optical fibres and (ii) wavelength sized apertures in thin films. In addition, a number of experimental techniques are explored with emphasis on the detection of small numbers of atoms near ultrathin optical fibres using both avalanche photodiodes and single photon detectors. A study on the interactions between atoms and photons is crucial for a full understanding of quantum mechanical processes at the few atom scale and detection schemes sensitive to very low levels of fluorescence from the laser-cooled atoms are vital for attaining this goal. Finally, an experimental study on the design and fabrication of arrays of silica microdisks, that could be used for facilitating interactions between cold atoms and photons, is presented."