| 研究課題/領域番号 |
19K23429
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| 研究機関 | 分子科学研究所 |
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研究代表者 |
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| 研究期間 (年度) |
2019-08-30 – 2021-03-31
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| キーワード | Quantum physics / Rydberg atoms / Dipole dipole coupling / Optical Tweezers |
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| 研究実績の概要 |
The objective is to study a system of 2 Rydberg atoms, closed enough (typ. 0.5-1 um) for their electronic orbitals to overlap. The plan is (1) to trap Rubidium (Rb) and Cesium (Cs) in submicron-sized optical tweezers, (2) to cool these atoms to < 1 uK (enough to remove oscillation of the atoms in the traps), and (3) to excite the atoms to Rydberg state and perform spectroscopy.
(1) is partially completed. Laser-cooled cloud of Rb and Cs atoms have been obtained; trapping and fluorescence imaging of single Rb atom in one optical tweezers have been observed, as well as trapping Rb atoms in an array of 20 holographic tweezers. The size of the tweezers (waist ~ 1.5 um, and trap frequency) have been characterized using the single atom as an in-situ probe. A higher performance optical system is being prepared to create smaller tweezers.
(2) is in preparation. The atom temperature T ~ 50 uK have been measured after sub-Doppler cooling. Setup for Raman-sideband cooling is being assembled. As a first necessary step, optical pumping and microwave Rabi oscillation on the clock transition of Rb have been demonstrated.
The laser systems required for step (3) are being assembled.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
The vacuum system, specially designed for experiments with cold Rydberg atoms, have been assembled and successfully brought to the Ultra-High Vacuum regime. A magneto-optical trap setup was installed and used to trap and cool Rb or Cs atomic clouds. An holographic optical system comprised of a Spatial Light Modulator and an objective system (NA = 0.45) was introduced to create arrays of optical tweezers inside each of which a single atom can be trapped with 50% probability. Trapping of single atoms was demonstrated by fluorescence imaging.
A first set of experiments with single atoms was conducted to measure the trap characteristics (depth, size) and the atom properties (trapping lifetime, temperature, fluorescence). Especially a trap size of ~ 1.5 um was measured, 2 to 3 times too large for the envisioned research project, and the reason was traced back to the current objective system (spherical aberrations), which should be solved in the next fiscal year.
A second set of experiments was then started to control the internal, electronic, degree of freedom of the atom. In particular, the atom was prepared in a single magnetic ground-state level (by optical pumping) and coherent Rabi oscillation between two ground states was demonstrated. However, experiments have halted since February because the laser system used to trap the atoms have broken and the company is still working on fixing the equipment.
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| 今後の研究の推進方策 |
A new custom-made objective system with high NA=0.75 will be installed to solve the tweezers-size problem. Preliminary characterization of the objective indicates that tweezers with a waist of 0.5 um is within reach.
Then, in order to prepare ordered atomic arrays despite the stochastic loading of each tweezers with only 50% probability, an automated moving tweezers will be integrated to the experiment to re-arrange the atom one-by-one. To further cool the atoms, down to the motional ground-state of the tweezers, the Raman-sideband cooling technique will be implemented.
Followingly, using the picosecond laser-pulse system being now assembled, I will excite the atoms from their electronic ground state to a Rydberg level. A first aim will be to increase the Rydberg population after the laser pulse from currently < 10% to ~ 50%. To this end, I will explore a new excitation scheme using resonant coupling to an intermediate state, rather than the usual off-resonance technique.
Finally, interactions between neighbouring Rydberg atoms will be investigated in a wide range of interatomic distance where the interaction should evolve from a perturbative van-der-Walls potential (large distance) to a situation where quantum effects play a key role (overlapping Rydberg orbitals).
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| 次年度使用額が生じた理由 |
Travel expenses have been less than expected due to the cancellation of international conferences following the coronavirus situation.
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