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arXiv:2007.01762 · Physical Review A

Controlling the ac Stark effect of RbCs with dc electric and magnetic fields

Jacob A. Blackmore, Rahul Sawant, Philip D. Gregory, Sarah Bromley, J. Aldegunde, Jeremy M. Hutson, Simon L. Cornish

Published Nov 17, 2020• 27 citations
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Abstract

Effects of static electric and magnetic fields on the differential ac Stark shifts for microwave transitions in ultracold bosonic ${}^{87}$Rb${}^{133}$Cs molecules are studied experimentally. The ac Stark effect is greatly simplified by applying a dc electric field in addition to the magnetic field.

DOI
10.1103/physreva.102.053316

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Effects of static electric and magnetic fields on the differential ac Stark shifts for microwave transitions in ultracold bosonic 87{}^{87}87Rb133{}^{133}133Cs molecules are studied experimentally. The ac Stark effect is greatly simplified by applying a dc electric field in addition to the magnetic field.
Polar molecules offer a new platform for quantum simulation of systems with long-range interactions, based on the electrostatic interaction between their electric dipole moments. Here, we report the development of coherent quantum state control using microwave fields in 40 Ca 19 F and 87 Rb 133 Cs molecules, a crucial ingredient for many quantum simulation applications. We perform Ramsey interferometry measurements with fringe spacings of ∼1 kHz and investigate the dephasing time of a superposition of N = 0 and N = 1 rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped 40 Ca 19 F we use a magnetically insensitive transition and observe a coherence time of 0.61(3) ms. For optically trapped 87 Rb 133 Cs we exploit an avoided crossing in the AC Stark shifts and observe a maximum coherence time of 0.75(6) ms.
Rydberg states of atoms and molecules are very sensitive to electric fields. This property makes them ideal electric-field sensors but is detrimental to applications of Rydberg states in quantum optics, quantum-information processing, and quantum simulation because of inhomogeneous Stark broadening and the resulting loss of quantum coherence. We demonstrate, with the example of Rydberg states of 39K^{39}\mathrm{K}39K, the existence of Rydberg-Rydberg transitions with extremely small differential dc Stark shifts, which we call dc-field-magic Rydberg-Rydberg transitions. These transitions hardly exhibit any Stark broadening, even when the electric-field strength varies by as much as $10\phantom{\rule{4pt}{0ex}}\mathrm{V}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ over the experimental volume. We present a systematic study of dc-field-magic Rydberg-Rydberg transitions combining experiment and calculations and classify them in three main types, which should also be encountered in the other alkali-metal atoms, in alkaline-earth-metal atoms, and even in molecules. The observed insensitivity to dc electric fields does not reduce the interactions between Rydberg atoms, even if they are dominantly electric dipole-dipole in nature. Rydberg states coupled by dc-field-magic Rydberg-Rydberg transitions, therefore, have great potential as qubits.
The response of an atom to external electric and magnetic fields can reveal fundamental atomic properties. It has long been verified that, in a static magnetic field, those atomic energy levels with hyperfine interactions shift according to the Breit-Rabi formula, which introduces nonlinear dependence on the magnetic field. On the other hand, the corresponding Breit-Rabi dependence on a static electric field has not been observed before due to a combination of experimental challenges. Here, we precisely measure the Stark shift of the [Formula: see text] transition of [Formula: see text]Yb ([Formula: see text] = 1/2) with cold atoms held by an optical dipole trap in a static electric field up to 120 kV/cm. We observe the electric Breit-Rabi effect displaying high-order ([Formula: see text] and [Formula: see text]) DC Stark shifts. These effects arise from the influence of the strong electric field on hyperfine interactions.
The thesis reports transferring the ultracold RbCs molecules to the absolute ground state and a trapping light that eliminates the differential AC Stark shift. We build a laser system to perform Stimulated Raman Adiabatic Passage (STIRAP) for the molecules trapped in tweezers, which transfer the molecules from the weakly- bounded state to the absolute ground state. We use the offset cavity stabilisation technique to stabilise the laser frequencies to a passive cavity to narrow the laser linewidths while keeping the laser frequency tunable. We then align the beams to the molecules. We demonstrate a “magic” laser frequency to eliminate the differential AC Stark shift of the rotational states in the ground vibrational state of RbCs molecule and to increase the rotational coherence time of multiple states. We study the AC Stark effect caused by the trapping light. We calculate the polarisabilities of the rotational states near a narrow electronic from X ^1Σ^+ state to b^3Π_0 state and found at certain laser frequency the polarisabilities become the same. We measure the transition frequencies to different vibrational states in the excited electronic state experimentally. We perform microwave spectroscopy to measure the light shift and show that the shift vanishes at the magic frequency. We confirmed the coherence in 1 ms timescale by measuring the Ramsey fringe contrast.
The ac Stark effect was used to induce resonant energy transfer between translationally cold 85Rb Rydberg atoms. When a 28.5 GHz dressing field was set at specific field strengths, the two-atom dipole-dipole process 43d5/2+43d5/2-->45p3/2+41f was dramatically enhanced, due to induced degeneracy of the initial and final states. This method for enhancing interactions is complementary to dc electric-field-induced resonant energy transfer, but has more flexibility due to the possibility of varying the applied frequency.