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Physical Review A

Characterization of a state-insensitive dipole trap for cesium atoms

Piyaphat Phoonthong, P. Douglas, Arne Wickenbrock, Ferruccio Renzoni

Published Jul 12, 2010• 17 citations
Publisher

Abstract

In this work we characterize a state-insensitive dipole trap for cold cesium atoms, as realized by tightly focusing a single running laser beam at the magic wavelength. The use of trapping light at the magic wavelength of $935.6$ nm resulted in the same ac Stark shift for the ${}^{6}{S}_{1/2}$ ground state and the ${}^{6}{P}_{3/2}$ excited state. A complete characterization of the trap is given, which includes the dependence of the lifetime on the trap depth, an analysis of the important role played by a depumper beam, and a comparison with dipole trapping at different (nonmagic) wavelengths. In particular, we measured the differential light shift of the relevant optical transition as a function of the trapping light wavelength, and showed that it becomes zero at the magic wavelength. Our results are compared to previous realizations of state-insensitive dipole traps for cesium atoms. We also discuss the possible role of the state-insensitive trap, its limitations, and possible developments for the study of ground-state quantum coherence phenomena and related applications.

DOI
10.1103/physreva.82.013406

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State-insensitive traps are an important tool for precision spectroscopy. \nIn these traps both the ground and excited state of the relevant atomic \ntransition are shifted by the same amount. To obtain state-insensitive \ntrapping, a specific trapping wavelength - called the "magic wavelength" - \nmust be used. This thesis describes state-insensitive trapping of caesium \natoms, as realised by using a trapping laser beam at the magic wavelength \nof 935.6 nm. Two different experimental setups were realised and \ncharacterised. \nThe first set of experiments provided the characterisation of a singlewell \nstate-insensitive trap, produced by using the laser beam from a Tisapphire \nlaser. The trap lifetime was determined as a function of the trap \ndepth, with the largest lifetime of 203 ms measured for a trap depth of 2.4 \nmK. Further improvement in the trap lifetime was obtained by applying \na depumper laser beam, which prepared the atoms in the lower ground \nstate. This suppresses hyperfine changing collisions, and the lifetime was \nincreased to 3.6 s as a result. Ultimately, the lifetime was limited by \nthe pointing instability of the dipole trap beam and the background gas \ncollisions. \nA second experimental setup was then realised, to reduce the background \ngas collisions, which is the limitation of lifetime in the first setup. \nFurthermore, the imaging system was upgraded to reduce the background \nnoise, and a MOPA system was used to produce the state-insensitive trap. \nIn a second set of experiments, a single-well trap and a 1D optical lattice \nwere compared to evaluate the suppression of two-body collisions in the \n1D lattice case.

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We calculate the optical potentials, i.e. the light shifts, of the ground and excited states of atomic cesium in a two-color evanescent field around a subwavelength-diameter fiber. We show that the light shifts of the $6S_{1/2}\leftrightarrow 6P_{3/2}$ transitions can be minimized by tuning one trapping light to around 934.5 nm in wavelength (central red-detuned magic wavelength) and the other light to around 685.5 nm in wavelength (central blue-detuned magic wavelength). The simultaneous use of the red- and blue-detuned magic wavelengths allows state-insensitive two-color trapping and guiding of cesium atoms along the thin fiber. Our results can be used to efficiently load a two-color dipole trap by cesium atoms from a magneto-optical trap and to perform continuous observations.

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Theoretical analysis of polarization-angle-dependent magic-wavelength optical dipole trap of Cs atoms

Jiandong Bai, Shuo Liu, Wen-Yuan Liu +2 more

Laser cooling and trapping of neutral atoms is of great significance for studying the physical and chemical properties of atoms. To further realize the spatial localization of atoms, optical dipole trap (ODT) was proposed to manipulate individual atoms, ions or molecules and has become an increasingly important technique in the field of cold atomic physics and quantum optics. To eliminate the differential light shift of transitions between atomic states, ODT can be turned off during excitation/radiation. However, it will shorten the trap lifetime of the atom and reduce the repetition rate of the single photon. The AC stark shift can be eliminated experimentally by constructing blue-detuned dark ODT, but the micron-level dark ODT usually requires more complex experimental equipment and is not easy to operate. Therefore, magic-wavelength ODT was constructed to realize that the transition frequency of photons between atomic states is the same as in free space. When the trapping laser makes the differential light shift of the transition between the two atomic states zero, the laser wavelength is called the magic wavelength. The magic-wavelength ODT can eliminate the differential light shift of the transition between atoms, improve the repetition rate of the experimental sequence and weaken the atomic decoherence. In recent years, it has become a powerful tool for manipulating cold atoms, especially for coherently manipulating the atomic inner states. In the present work, with the theory of multi-level model, we calculate the dynamic electric polarizability of the 6S1/2 ground state and the 6P3/2 excited state connecting the D2 line of cesium atom in a range of 800–1000 nm, and obtain the magic wavelength of the optical trapping laser to trap the ground state and the excited state. Since the polarizability of atomic states with angular momentum greater than 0.5 is very sensitive to the polarization angle, the polarization-angle-dependent magic wavelength and the corresponding magic polarizability are analyzed by taking the linearly-polarized trapping laser for example. The magic polarization angle is 54.7° and the magic wavelength at this angle are 886.4315 and 934.0641 nm, respectively. The robustness of the magic conditions and the feasibility of the experimental operation are further analyzed.

Acta Physica Sinica•Jan 1, 2023•2 citations
In this work we characterize a state-insensitive dipole trap for cold cesium atoms, as realized by tightly focusing a single running laser beam at the magic wavelength. The use of trapping light at the magic wavelength of 935.6935.6935.6 nm resulted in the same ac Stark shift for the 6S1/2{}^{6}{S}_{1/2}6S1/2​ ground state and the 6P3/2{}^{6}{P}_{3/2}6P3/2​ excited state. A complete characterization of the trap is given, which includes the dependence of the lifetime on the trap depth, an analysis of the important role played by a depumper beam, and a comparison with dipole trapping at different (nonmagic) wavelengths. In particular, we measured the differential light shift of the relevant optical transition as a function of the trapping light wavelength, and showed that it becomes zero at the magic wavelength. Our results are compared to previous realizations of state-insensitive dipole traps for cesium atoms. We also discuss the possible role of the state-insensitive trap, its limitations, and possible developments for the study of ground-state quantum coherence phenomena and related applications.
State-insensitive traps are an important tool for precision spectroscopy. \nIn these traps both the ground and excited state of the relevant atomic \ntransition are shifted by the same amount. To obtain state-insensitive \ntrapping, a specific trapping wavelength - called the "magic wavelength" - \nmust be used. This thesis describes state-insensitive trapping of caesium \natoms, as realised by using a trapping laser beam at the magic wavelength \nof 935.6 nm. Two different experimental setups were realised and \ncharacterised. \nThe first set of experiments provided the characterisation of a singlewell \nstate-insensitive trap, produced by using the laser beam from a Tisapphire \nlaser. The trap lifetime was determined as a function of the trap \ndepth, with the largest lifetime of 203 ms measured for a trap depth of 2.4 \nmK. Further improvement in the trap lifetime was obtained by applying \na depumper laser beam, which prepared the atoms in the lower ground \nstate. This suppresses hyperfine changing collisions, and the lifetime was \nincreased to 3.6 s as a result. Ultimately, the lifetime was limited by \nthe pointing instability of the dipole trap beam and the background gas \ncollisions. \nA second experimental setup was then realised, to reduce the background \ngas collisions, which is the limitation of lifetime in the first setup. \nFurthermore, the imaging system was upgraded to reduce the background \nnoise, and a MOPA system was used to produce the state-insensitive trap. \nIn a second set of experiments, a single-well trap and a 1D optical lattice \nwere compared to evaluate the suppression of two-body collisions in the \n1D lattice case.
We calculate the optical potentials, i.e. the light shifts, of the ground and excited states of atomic cesium in a two-color evanescent field around a subwavelength-diameter fiber. We show that the light shifts of the 6S1/2leftrightarrow6P3/26S_{1/2}\\leftrightarrow 6P_{3/2}6S1/2​leftrightarrow6P3/2​ transitions can be minimized by tuning one trapping light to around 934.5 nm in wavelength (central red-detuned magic wavelength) and the other light to around 685.5 nm in wavelength (central blue-detuned magic wavelength). The simultaneous use of the red- and blue-detuned magic wavelengths allows state-insensitive two-color trapping and guiding of cesium atoms along the thin fiber. Our results can be used to efficiently load a two-color dipole trap by cesium atoms from a magneto-optical trap and to perform continuous observations.
Optical dipole traps (ODT) with far-off-resonance laser are important tools in more and more present cold-atom experiments, which allow confinement of laser-cooled atoms with a long storage time. Particularly, the magic wavelength ODT can cancel the position-dependent spatially inhomogeneous light shift of desired atomic transition, which is introduced by the ODT laser beam. Now it plays an important role in the state-insensitive quantum engineering and the atomic optical clock. To verify the magic wavelength or the magic wavelength combination for D2 line transition of cesium (Cs) and rubidium (Rb) atoms, we calculated and analyzed the light shift of the 133Cs 6S1/2 - 6P3/2 transition for a monochromatic ODT, and also the 87Rb 5S1/2 - 5P3/2 transition for a dichromatic ODT with a laser frequency ratio of 2:1. Also a dichromatic magic-wavelength ODT laser system for 87Rb atoms is proposed and experimentally realized by employing the quasi-phase-matched frequency doubling technique with telecom laser and fiber amplifier.
For the trapped pre-cooled atoms in an optical dipole trap (ODT), the magic-wavelength ODT can eliminate the differential light shift of the transition between two atomic states, so that the transition frequency between the two states is the same as that of atoms in the free space, which is of great significance for improving the experimental repetition rate and reducing the atomic decoherence in the fields of cold atom physics, quantum optics, and precision measurement. Here we calculate the dynamic polarizabilities of cesium 6S ground state and 7P excited state by using the multi-level model for the ODT with laser wavelength from 1200 to 2000 nm. The magic wavelengths of ODT are obtained for the linearly and circularly polarized laser beams at the intersection of dynamic polarizabilities of two atomic states. Furthermore, we analyze the robustness of the magic trapping conditions and the feasibility of the experimental operation near the telecom C-band wavelength.
We calculate the optical potentials, i.e. the light shifts, of the ground and excited states of atomic cesium in a two-color evanescent field around a subwavelength-diameter fiber. We show that the light shifts of the 6S1/2↔6P3/26S_{1/2}\leftrightarrow 6P_{3/2}6S1/2​↔6P3/2​ transitions can be minimized by tuning one trapping light to around 934.5 nm in wavelength (central red-detuned magic wavelength) and the other light to around 685.5 nm in wavelength (central blue-detuned magic wavelength). The simultaneous use of the red- and blue-detuned magic wavelengths allows state-insensitive two-color trapping and guiding of cesium atoms along the thin fiber. Our results can be used to efficiently load a two-color dipole trap by cesium atoms from a magneto-optical trap and to perform continuous observations.
Laser cooling and trapping of neutral atoms is of great significance for studying the physical and chemical properties of atoms. To further realize the spatial localization of atoms, optical dipole trap (ODT) was proposed to manipulate individual atoms, ions or molecules and has become an increasingly important technique in the field of cold atomic physics and quantum optics. To eliminate the differential light shift of transitions between atomic states, ODT can be turned off during excitation/radiation. However, it will shorten the trap lifetime of the atom and reduce the repetition rate of the single photon. The AC stark shift can be eliminated experimentally by constructing blue-detuned dark ODT, but the micron-level dark ODT usually requires more complex experimental equipment and is not easy to operate. Therefore, magic-wavelength ODT was constructed to realize that the transition frequency of photons between atomic states is the same as in free space. When the trapping laser makes the differential light shift of the transition between the two atomic states zero, the laser wavelength is called the magic wavelength. The magic-wavelength ODT can eliminate the differential light shift of the transition between atoms, improve the repetition rate of the experimental sequence and weaken the atomic decoherence. In recent years, it has become a powerful tool for manipulating cold atoms, especially for coherently manipulating the atomic inner states. In the present work, with the theory of multi-level model, we calculate the dynamic electric polarizability of the 6S1/2 ground state and the 6P3/2 excited state connecting the D2 line of cesium atom in a range of 800–1000 nm, and obtain the magic wavelength of the optical trapping laser to trap the ground state and the excited state. Since the polarizability of atomic states with angular momentum greater than 0.5 is very sensitive to the polarization angle, the polarization-angle-dependent magic wavelength and the corresponding magic polarizability are analyzed by taking the linearly-polarized trapping laser for example. The magic polarization angle is 54.7° and the magic wavelength at this angle are 886.4315 and 934.0641 nm, respectively. The robustness of the magic conditions and the feasibility of the experimental operation are further analyzed.