Indistinguishability of 852 nm single-photon source based on a single cesium atom trapped in a magic wavelength optical tweezer (Conference Presentation)
Junmin Wang, Bei Liu, Rui Sun, Jiachao Wang, Xin Wang, Gang Y Jin, Jun He
Atoms trapped in magic-wavelength optical tweezer will have the same light shift for the desired ground and excited states. In this case the position-dependence differential light shift of the desired transition can be eliminated. For cesium 6S_1/2 (Fg = 4, mF = +4) - 6P_3/2 (Fe = 5, mF = +5) cycling transition (852 nm), the magic wavelength was calculated theoretically for a linearly-polarized optical tweezer, and also it was verified experimentally to be 937.6 nm. We have demonstrated 852-nm triggered single-photon sources based on single cesium atom trapped in linearly-polarized optical tweezers implemented by using of 1064-nm and 937.6-nm lasers, respectively. The photon statistics were characterized by using of the Hanbury Brown - Twiss (HBT) scheme based on Si single-photon detectors (SSPDs). Strong anti-bunching effect [g^2(t=0) = 0.09] was recognized, and it shown perfectly the single-photon characters. The Hong-Ou-Mandel (HOM) two-photon interference measurements based on SSPDs were employed to evaluate the photon indistinguishability. Our preliminary experimental results indicated that the indistinguishability of single photons has been improved ~ 20% for the case of magic-wavelength optical tweezer. References: [1] Phys. Rev. A 94 (2016) 013409; [2] Appl. Phys. Express 9 (2016) 072702; [3] Opt. Express 25 (2017) p.15861
Atoms trapped in magic-wavelength optical tweezer will have the same light shift for the desired ground and excited states. In this case the position-dependence differential light shift of the desired transition can be eliminated. For cesium 6S_1/2 (Fg = 4, mF = +4) - 6P_3/2 (Fe = 5, mF = +5) cycling transition (852 nm), the magic wavelength was calculated theoretically for a linearly-polarized optical tweezer, and also it was verified experimentally to be 937.6 nm. We have demonstrated 852-nm triggered single-photon sources based on single cesium atom trapped in linearly-polarized optical tweezers implemented by using of 1064-nm and 937.6-nm lasers, respectively. The photon statistics were characterized by using of the Hanbury Brown - Twiss (HBT) scheme based on Si single-photon detectors (SSPDs). Strong anti-bunching effect [g^2(t=0) = 0.09] was recognized, and it shown perfectly the single-photon characters. The Hong-Ou-Mandel (HOM) two-photon interference measurements based on SSPDs were employed to evaluate the photon indistinguishability. Our preliminary experimental results indicated that the indistinguishability of single photons has been improved ~ 20% for the case of magic-wavelength optical tweezer. References: [1] Phys. Rev. A 94 (2016) 013409; [2] Appl. Phys. Express 9 (2016) 072702; [3] Opt. Express 25 (2017) p.15861
Single-atom-based single-photon source has several advantages, such as narrow bandwidth, wavelength matching with the absorption line of the same atomic ensemble, and insensitivity to the environment disturbing, and it is very important not only for basic researches in quantum optic field but also for applications in quantum information processing. In this paper, we report the generation of a 10-MHz-repetition-rate triggered single-photon source at 852 nm based on a trapped single cesium atom in a far-off-resonance microscopic optical dipole trap (FORT). To generate an optical dipole trap, a far-red-detuned 1064 nm laser beam is tightly focused by using a high numerical aperture lens, a typical trap depth is 2 mK and trap waist is 2.3 m. To obtain a maximum probability of pulsed excitation, the frequency of the pulsed laser should be resonant with the atomic energy levels and the trapped single atom must be excited with a -pulse. However, the interaction between the FORT laser and the atoms causes AC Stark shifts of the atomic energy levels. Thus, in order to demonstrate the resonant pulsed excitation, it is important to calculate and measure the shift of 6S1/2|Fg=4,mF=+4-6P3/2|Fe=5,mF=+5 cyclical transition in the FORT. For a two-level system, the probability of pulsed excitation can be described by Rabi oscillations with a characteristic Rabi frequency . With an optimized time sequence, we experimentally demonstrate the Rabi oscillation between the ground state and the excited state, and the peak power of -pulse laser is about 1.25 mW. We also measure the temporal envelope of single photons after a -pulse excitation. A gated pulsed excitation and cooling technique are used to reduce the possibility that atoms are heated by -pulse laser. The typical trapping lifetime of single cesium atom is extended from~108 ups to~2536 ms. The corresponding number of excitations is improved from 108 to 360000. The second-order intensity correlations of the emitted single-photon are characterized by implementing Hanbury Brown-Twiss setup. The statistics shows a strong anti-bunching with a value of 0.09 for the second-order correlation at zero delay. In the future, we will perform a Hong-Ou-Mandel two-photon interference experiment to analyze the indistinguishability of the single photons. We will also trap single atoms in a magic-wavelength optical dipole trap where the ground and the excited states have the same shift.
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.
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.
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.
Abstract A magic-wavelength optical dipole trap (ODT) can eliminate the differential light shift of the transition between atomic states, so that transition frequency between the two states is the same as that in free space, which is of great significance for exploring atomic structure. Here we calculate the dynamic polarizabilities of the 6S1/2 ground state and 6P1/2 excited state of the cesium atom which are connected by the D1 line, by using the relativistic coupled cluster method, and obtain magic wavelengths of ODT laser for trapping the two states simultaneously. By using these magic wavelengths, we calculate oscillator strength of the 6P1/2 → 7D3/2 transition for linearly and circularly polarized lights. Furthermore, we analyze the influence of magic wavelengths on oscillator strengths.
Abstract A magic-wavelength optical dipole trap (ODT) can eliminate the differential light shift of transition between atomic states, so that the transition frequency between the two states is the same as that in free space, which is of great significance for exploring atomic structure. Here we calculate the dynamic polarizabilities of the 6S1/2 ground state and the 6P1/2 excited state of the cesium atom which are connected by the D1 line, by using the relativistic coupled cluster method, and obtain magic wavelengths of ODT laser for trapping the two states simultaneously. By using these magic wavelengths, we calculate oscillator strengths of the 6P1/2 → 7D3/2 transition for linearly and circularly polarized lights. Furthermore, we analyze the influence of magic wavelengths on oscillator strengths.