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State-insensitive traps for caesium atoms

Piyaphat Phoonthong

Published Feb 28, 2012• 1 citation
OpenAlex

Abstract

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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State-insensitive trapping plays a significant role in many cold atom experiments. In this technique, trapping at a specific "magic" wavelength leads to identical shifts of the ground and excited states of a particular transition. Hence, the internal state of the trapped atoms remains essentially unaffected by the trapping light. This leads to increased coherence times and loading efficiency, and allows for the use of free-space manipulation techniques. However, the applicability of state-insensitive trapping is limited in terms of light sources available, with restrictions coming from either the required frequency or power. In this thesis, state-insensitive trapping of caesium atoms is considered. It can be achieved at the wavelength of 935.6 nm. However, the present work shows that this wavelength is impractical for experimental realizations of atom trapping in free space due to lack of laser sources with sufficiently high power. We therefore propose bichromatic trapping, as produced by two independent laser fields with different frequencies, to overcome the limitations related to monochromatic trapping. We show that bichromatic trapping extends the range of possible magic wavelengths compared to the specific magic wavelength associated with monochromatic trapping. Specifically, we present results for the magic wavelength combinations for caesium atoms with particular attention to the frequency range of currently available laser sources. Simultaneous state-independent trapping of atomic mixtures of caesium with rubidium and lithium atoms was also investigated, and appropriate magic wavelength combinations were identified. Additionally, species-selective state-independent trapping of atomic mixtures of caesium and lithium was explored and common wavelength pairs for tune-out and magic wavelengths of these atoms were determined.

•Apr 28, 2016•0 citations

Characterization of a state-insensitive dipole trap for cesium atoms

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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.

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State-insensitive dipole trapping of multilevel atoms can be achieved by an appropriate choice of the wavelength of the trapping laser, so that the interaction with the different transitions results in equal AC Stark shifts for the ground and excited states of interest. However, this approach is severely limited by the availability of coherent sources at the required wavelength and of appropriate power. This work investigates state-insensitive trapping of caesium atoms for which the required wavelength of 935.6 nm is inconvenient in terms of experimental realization. Bichromatic state-insensitive trapping is proposed to overcome the lack of suitable laser sources. We first consider pairs of laser wavelengths in the ratio 1:2 and 1:3, as obtained via second- and third-harmonic generation. We found that the wavelength combinations 931.8–1863.6 nm and 927.5–2782.5 nm are suitable for state-insensitive trapping of caesium atoms. In addition, we examine bichromatic state-insensitive trapping produced by pairs of laser wavelengths corresponding to currently available high-power lasers. These wavelength pairs were found to be in the range of 585–588 nm and 623–629 for one laser and 1064–1080 nm for the other.

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State-insensitive dipole trapping of multilevel atoms can be achieved by an appropriate choice of the wavelength of the trapping laser, so that the interaction with the different transitions results in equal AC Stark shifts for the ground and excited states of interest. However this approach is severely limited by the availability of coherent sources at the required wavelength and of appropriate power. This work investigates state-insensitive trapping of caesium atoms for which the required wavelength of 935.6 nm is inconvenient in terms of experimental realization. Bichromatic state-insensitive trapping is proposed to overcome the lack of suitable laser sources. We first consider pairs of laser wavelengths in the ratio 1:2 and 1:3, as obtained via second- and third- harmonic generation. We found that the wavelength combinations 931.8-1863.6 nm and 927.5-2782.5 nm are suitable for state-insensitive trapping of caesium atoms. In addition, we examine bichromatic state-insensitive trapping produced by pairs of laser wavelengths corresponding to currently available high power lasers. These wavelength pairs were found to be in the range of 585-588 nm and 623-629 for one laser and 1064-1080 nm for the other.

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We demonstrate magic wavelengths for the $6s ~ {^2}S_{1/2}-6p ~ {^2}P_{3/2,1/2}$ transitions in the Cs atom due to the circularly polarized light. In addition, we also obtain magic wavelengths using the linearly polarized light in order to verify the previously reported values and make a comparative study with the values obtained for the circularly polarized light. Most of these wavelengths are found to be in the optical region and could be of immense interest to the experimentalists for carrying out high precision measurements. To obtain these wavelengths, we have calculated dynamic dipole polarizabilities of the ground, $6p ~{^2}P_{1/2}$ and $6p ~{^2}P_{3/2}$ states. We use the available precise values of the electric dipole (E1) matrix elements for the most dominantly contributing transitions from the lifetime measurements of the above excited states and obtain other relevant important E1 matrix elements by employing a relativistic coupled-cluster method approximating at the singles and doubles level. Accuracies in these quantities are substantiated by comparing our evaluated scalar polarizability values with the corresponding experimental results.

•Jan 4, 2016•0 citations

Magic wavelengths for the 6S-7P transition of cesium atoms

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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.

Results in Physics•Aug 12, 2023•2 citations
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.
State-insensitive trapping plays a significant role in many cold atom experiments. In this technique, trapping at a specific "magic" wavelength leads to identical shifts of the ground and excited states of a particular transition. Hence, the internal state of the trapped atoms remains essentially unaffected by the trapping light. This leads to increased coherence times and loading efficiency, and allows for the use of free-space manipulation techniques. However, the applicability of state-insensitive trapping is limited in terms of light sources available, with restrictions coming from either the required frequency or power. In this thesis, state-insensitive trapping of caesium atoms is considered. It can be achieved at the wavelength of 935.6 nm. However, the present work shows that this wavelength is impractical for experimental realizations of atom trapping in free space due to lack of laser sources with sufficiently high power. We therefore propose bichromatic trapping, as produced by two independent laser fields with different frequencies, to overcome the limitations related to monochromatic trapping. We show that bichromatic trapping extends the range of possible magic wavelengths compared to the specific magic wavelength associated with monochromatic trapping. Specifically, we present results for the magic wavelength combinations for caesium atoms with particular attention to the frequency range of currently available laser sources. Simultaneous state-independent trapping of atomic mixtures of caesium with rubidium and lithium atoms was also investigated, and appropriate magic wavelength combinations were identified. Additionally, species-selective state-independent trapping of atomic mixtures of caesium and lithium was explored and common wavelength pairs for tune-out and magic wavelengths of these atoms were determined.
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 dipole trapping of multilevel atoms can be achieved by an appropriate choice of the wavelength of the trapping laser, so that the interaction with the different transitions results in equal AC Stark shifts for the ground and excited states of interest. However, this approach is severely limited by the availability of coherent sources at the required wavelength and of appropriate power. This work investigates state-insensitive trapping of caesium atoms for which the required wavelength of 935.6 nm is inconvenient in terms of experimental realization. Bichromatic state-insensitive trapping is proposed to overcome the lack of suitable laser sources. We first consider pairs of laser wavelengths in the ratio 1:2 and 1:3, as obtained via second- and third-harmonic generation. We found that the wavelength combinations 931.8–1863.6 nm and 927.5–2782.5 nm are suitable for state-insensitive trapping of caesium atoms. In addition, we examine bichromatic state-insensitive trapping produced by pairs of laser wavelengths corresponding to currently available high-power lasers. These wavelength pairs were found to be in the range of 585–588 nm and 623–629 for one laser and 1064–1080 nm for the other.
State-insensitive dipole trapping of multilevel atoms can be achieved by an appropriate choice of the wavelength of the trapping laser, so that the interaction with the different transitions results in equal AC Stark shifts for the ground and excited states of interest. However this approach is severely limited by the availability of coherent sources at the required wavelength and of appropriate power. This work investigates state-insensitive trapping of caesium atoms for which the required wavelength of 935.6 nm is inconvenient in terms of experimental realization. Bichromatic state-insensitive trapping is proposed to overcome the lack of suitable laser sources. We first consider pairs of laser wavelengths in the ratio 1:2 and 1:3, as obtained via second- and third- harmonic generation. We found that the wavelength combinations 931.8-1863.6 nm and 927.5-2782.5 nm are suitable for state-insensitive trapping of caesium atoms. In addition, we examine bichromatic state-insensitive trapping produced by pairs of laser wavelengths corresponding to currently available high power lasers. These wavelength pairs were found to be in the range of 585-588 nm and 623-629 for one laser and 1064-1080 nm for the other.
We demonstrate magic wavelengths for the 6s 2S1/2−6p 2P3/2,1/26s ~ {^2}S_{1/2}-6p ~ {^2}P_{3/2,1/2}6s 2S1/2​−6p 2P3/2,1/2​ transitions in the Cs atom due to the circularly polarized light. In addition, we also obtain magic wavelengths using the linearly polarized light in order to verify the previously reported values and make a comparative study with the values obtained for the circularly polarized light. Most of these wavelengths are found to be in the optical region and could be of immense interest to the experimentalists for carrying out high precision measurements. To obtain these wavelengths, we have calculated dynamic dipole polarizabilities of the ground, 6p 2P1/26p ~{^2}P_{1/2}6p 2P1/2​ and 6p 2P3/26p ~{^2}P_{3/2}6p 2P3/2​ states. We use the available precise values of the electric dipole (E1) matrix elements for the most dominantly contributing transitions from the lifetime measurements of the above excited states and obtain other relevant important E1 matrix elements by employing a relativistic coupled-cluster method approximating at the singles and doubles level. Accuracies in these quantities are substantiated by comparing our evaluated scalar polarizability values with the corresponding experimental results.
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.