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Steering photoassociation of cold 85 Rb atoms by two-color slowly-turned-on and rapidly-turned-oﬀ laser pulses

Journal of Physics B: Atomic Molecular and Optical Physics

September 2023
56(19)

DOI:10.1088/1361-6455/acf53e

Authors:

Bina Fu

Dalian Institute of Chemical Physics

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Photoassociation (PA) of ⁸⁵ Rb atoms from the ground X ¹ Σ ⁺ g state to the excited A ¹ Σ ⁺ g and b ³ Π u states by two-color laser pulses at 100 µK×k B is investigated by using quantum wavepacket method. Two pulses with detunings δ 1 and δ 2 varying from -1.0 to 1.0 cm ⁻¹ are taken into account. The speciﬁc case δ 1 = -δ 2 is generalized to the condition of arbitrary combination of δ 1 and δ 2 for both the Gaussian-pulse ﬁeld and the slowly-turned-on and rapidly-turned-oﬀ (STRT) ﬁeld. It is found that the introduce of the detunings in the two pluses can enhance the asymmetry of the time proﬁle and broaden the linewidth of the laser ﬁeld. The two factors can further enhance the PA probability for both resonant and nonresonant regions. Compared to the Gaussian ﬁeld, the STRT ﬁeld which is even more asymmetric in time proﬁle and more broaden in linewidth can signiﬁcantly enhance the PA probability, with the nonresonant transition dominating the PA process. It can be expected that once the two detunings are both positive, which is a relatively loose restriction for coherent control, a considerable PA probability can be obtained in a two-color STRT ﬁeld.

(a) The potential energy curves X1Σg+ , A1Σu+ and b3Πg+ and the schematic PA process of the ⁸⁵Rb + ⁸⁵Rb system. (b) The modular squares of the dipole matrix elements (MSDMEs) between the initial state and excited electronic states for vʹ = 450–569. The partially enlarged detail of MSDMEs for vʹ = 450–500 is shown in the inset.

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(a) The envelope |S(t)| of the two-color Gaussian pulses at |δω| = 0.0, 0.4, and 0.55 cm⁻¹. (b) The final populations Pres , Pnonres , Ptot versus the frequency difference |δω| after the action of the two-color Gaussian pulses. Here, δ1=−δ2 .

…

The wavepackets of the excited states versus t and vʹ driven by two-color Gaussian pulses at (a) |δω| = 0, (b) 0.55 and (c) 1.0 cm⁻¹. Here, δ1=−δ2 .

…

(a) The envelope |S(t)| of the two-color STRT pulses at |δω| = 0.0, 0.4, and 0.55 cm⁻¹. (b) The final populations Pres , Pnonres , Ptot versus frequency difference |δω| after the action of the two-color STRT pulses. Here, δ1=−δ2 .

…

The comparisons of the final populations (a) Pres , (b) Pnonres , (c) Ptot versus frequency difference |δω| between the situations of two-color Gaussian pulses (black curve) and the two-color STRT pulses (red curve). Here, δ1=−δ2 .

…

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Journal of Physics B: Atomic, Molecular and Optical Physics

J. Phys. B: At. Mol. Opt. Phys. 56 (2023) 195201 (11pp) https://doi.org/10.1088/1361-6455/acf53e

Steering photoassociation of cold 85Rb

atoms by two-color slowly-turned-on

and rapidly-turned-off laser pulses

Rong Zhang1, Jin-Wei Hu2, Gao-Ren Wang1, Bina Fu3and Yong-Chang Han1,4,5,∗

1Department of Physics, Dalian University of Technology, Dalian 116024, People’s Republic of China

2Department of Physics, Shanxi Vocational University of Engineering and Technology, Jinzhong 030619,

People’s Republic of China

3State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese

Academy of Sciences, Dalian 116023, People’s Republic of China

4DUT-BSU Joint Institute, Dalian University of Technology, Dalian 116024, People’s Republic of China

5Dalian Key Laboratory of Quantum Technology, Dalian University of Technology, Dalian 116024,

People’s Republic of China

E-mail: ychan@dlut.edu.cn

Received 24 May 2023, revised 16 August 2023

Accepted for publication 30 August 2023

Published 8 September 2023

Abstract

Photoassociation (PA) of 85Rb atoms from the ground X1Σ+

gstate to the excited A1Σ+

gand

b3Πustates by two-color laser pulses at 100 µK×kBis investigated by using quantum

wavepacket method. Two pulses with detunings δ1and δ2varying from −1.0 to 1. cm−1are

taken into account. The specic case δ1=−δ2is generalized to the condition of arbitrary

combination of δ1and δ2for both the Gaussian-pulse eld and the slowly-turned-on and

rapidly-turned-off (STRT) eld. It is found that the introduce of the detunings in the two pluses

can enhance the asymmetry of the time prole and broaden the linewidth of the laser eld. The

two factors can further enhance the PA probability for both resonant and nonresonant regions.

Compared to the Gaussian eld, the STRT eld which is even more asymmetric in time prole

and more broaden in linewidth can signicantly enhance the PA probability, with the

nonresonant transition dominating the PA process. It can be expected that once the two

detunings are both positive, which is a relatively loose restriction for coherent control, a

considerable PA probability can be obtained in a two-color STRT eld.

Keywords: photoassociation, slowly-turned-on and rapidly-turned-off pulses, 85Rb, detuning

(Some gures may appear in colour only in the online journal)

1. Introduction

Cold molecules have aroused much interest from researchers

[1–5], due to the wide applications in areas such as the meas-

urement of fundamental physical constants [6–8], quantum

information [9,10] and collision reaction [11–14]. In order

to produce cold molecules, researchers proposed direct and

∗Author to whom any correspondence should be addressed.

indirect methods. For the direct method, one can cool

molecules by using buffer gas cooling [15,16] or Stark

deceleration cooling [17,18]. The temperature of yield

molecules through directly cooling method can reach ∼mK

region. Starting from the relevant ultracold atoms, one can

form even colder molecules (lower than mK) via indirectly

cooling methods, such as photoassociation (PA) [19–22] or

magnetoassociation [23–25].

Among the indirect methods of preparing ultracold

molecules, PA is an efcient one with which the generated

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