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arXiv:2509.11968 · Physical Review A

Formation of oriented polar molecules with a single shaped pulse

Murilo Deliberali Forlevesi, Edson Denis Leonel, Emanuel F. de Lima

Published Dec 15, 2025• 0 citations
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Abstract

We explore the possibility of forming a oriented polar molecule directly from a pair of colliding atoms. The process comprises the photoassociation and vibrational stabilization along with the molecular orientation. These processes are driven by a single time-dependent, linearly polarized control field and proceeds entirely within the electronic ground state, leveraging the presence of a permanent dipole moment. The control field is found by means of an optimal quantum control algorithm with a single target observable given by the restriction of the orientation operator on a subset of bound levels. We consider a rovibrational model system for the collision of O + H atoms and solve directly the time-dependent Schrodinger equation. We show that the optimized field is capable of enhancing the molecular orientation already induced by the photoassociation and vibrational stabilization thus yielding oriented polar molecules that can be useful for many applications.

DOI
10.1103/xc55-v6xx

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We explore the possibility of forming a oriented polar molecule directly from a pair of colliding atoms. The process comprises the photoassociation and vibrational stabilization along with the molecular orientation. These processes are driven by a single time-dependent, linearly polarized control field and proceeds entirely within the electronic ground state, leveraging the presence of a permanent dipole moment. The control field is found by means of an optimal quantum control algorithm with a single target observable given by the restriction of the orientation operator on a subset of bound levels. We consider a rovibrational model system for the collision of O + H atoms and solve directly the time-dependent Schrodinger equation. We show that the optimized field is capable of enhancing the molecular orientation already induced by the photoassociation and vibrational stabilization thus yielding oriented polar molecules that can be useful for many applications.
We consider the formation of cold ground-state polar molecules in a low vibrational level by laser fields. Starting from a pair of cold colliding atoms of dissimilar species, we propose a strategy consisting of three steps. In the first step, a pump pulse induces the molecule formation by photoassociating the atomic pair in a high or intermediate vibrational level of an excited electronic molecular state. This step is followed by a dump pulse in an intermediate vibrational level of the ground state. The last step corresponds to the vibrational cooling or vibrational stabilization process. Taking advantage of the permanent dipole moment, an infrared chirped pulse induces downward transitions among the vibrational levels of the ground electronic state, reaching the ground vibrational level. We perform the strategy with with fixed-shaped pulses and also with an optimized chirped pulse for the stabilization step. To perform the optimization, we introduce an optimal control technique in which the optimization of the chirping is carried out in the time domain. This methodology has the benefit of limiting the pulse amplitude while focusing only on the frequency of the field. The proposed scheme is an alternative to the use of two pairs of pump-dump pulses or to the direct photoassociation and vibrational stabilization in the ground state.
Photoassociation of ultracold atoms with pulsed laser light is shown to lead to alignment of the product molecules along the excitation laser polarization axis. We theoretically investigate pulsed two-photon photoassociation of 87Rb^{87}\mathrm{Rb}87Rb atoms into a specific weakly bound level of the $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}$ metastable electronic state and find both stationary and time-dependent field-free alignment. Although a transform-limited pulse yields significant alignment, a frequency-chirped pulse dramatically enhances the ultracold molecular formation rate at the cost of a slight decrease in the alignment. Employing multiple pulses synchronized with the vibrational and rotational periods leads to coherent enhancement of both population and alignment of the target state. Inclusion of the rotational degree of freedom in the model gives rise to processes with multiple quantum paths, which lead to quantum effects such as interference and coherence revivals.
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The formation of the NaH molecule from unaligned ultracold atoms via photoassociation (PA) is theoretically investigated by numerically solving the time-dependent Schrödinger equation including the vibrational and rotational degrees of freedom. The PA processes via one- and two-photon excitations are described. The calculated results show that the associated molecule can be prepared to a desired rovibrational state of the ground electronic state for NaH. Compared with the one-photon association probability, the two-photon association probability is obviously enhanced.
Photoassociation is a possible route for the formation of chemical bonds. In this process, the binding of colliding atoms can be induced by means of a laser field. Photoassociation has been studied in the ultracold regime and also with temperatures well above millikelvins in the thermal energy domain, which is a situation commonly encountered in the laboratory. A photoassociation mechanism can be envisioned based on the use of infrared pulses to drive a transition from free colliding atoms on the electronic ground state to form a molecule directly on that state. This work takes a step in this direction, investigating the laser-pulse-driven formation of heteronuclear diatomic molecules in a thermal gas of atoms including rotational effects. Based on the assumption of full system controllability, the maximum possible photoassociation yield is deduced. The photoassociation probability is calculated as a function of the laser parameters for different temperatures. Additionally, the photoassociation yield induced by subpicosecond pulses of a priori fixed shape is compared to the maximum possible yield.
We consider the formation of cold diatomic molecules in the electronic ground state by photoassociation of atoms of dissimilar species. A combination of two transition pathways from the free colliding pair of atoms to a bound vibrational level of the electronic molecular ground state is envisioned. The first pathway consists of a pump-dump scheme with two time-delayed laser pulses in the near-infrared frequency domain. The pump pulse drives the transition to a bound vibrational level of an excited electronic state, while the dump pulse transfers the population to a bound vibrational level of the electronic ground state. The second pathway takes advantage of the existing permanent dipole moment and employs a single pulse in the far-infrared domain to drive the transition from the unbound atoms directly to a bound vibrational level in the electronic ground state. We show that this scheme offers the possibility to coherently control the photoassociation yield by manipulating the relative phase and timing of the pulses. The photoassociation mechanism is illustrated for the formation of cold LiCs molecules.