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arXiv:1807.05787 · Physical Review A

Controlling ultracold p -wave collisions with nonresonant light: Predictions of an asymptotic model

A. Crubellier, Rosario González‐Férez, Christiane P. Koch, Eliane Luc-Koenig

Published Mar 25, 2019• 5 citations
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Abstract

Interactions in a spin-polarized ultracold Fermi gas are governed by $p$-wave collisions and can be characterized by the $p$-wave scattering volume. Control of these collisions by Feshbach resonances is hampered by huge inelastic losses. Here, we suggest nonresonant light control of $p$-wave collisions, exploiting the anisotropic coupling of nonresonant light to the polarizability of the atoms. The $p$-wave scattering volume can be controlled by strong nonresonant light, in close analogy to the $s$-wave scattering length. For collision partners that are tightly trapped, the nonresonant light induces an energy shift directly related to the scattering volume (as defined by A. Crubellier, R. Gonz\'alez-F\'erez, C. P. Koch, and E. Luc-Koenig, preceding paper, Phys. Rev. A 99, 032709 (2019). This effect could be used to climb the ladder of the trap. We also show that controlling the scattering volume implies control, at least roughly, over the orientation at short interatomic distances of the interparticle axis relative to the polarization direction of the light. Our proposal is based on an asymptotic model that explicitly accounts for the anisotropic dipole-dipole interaction which governs the ultracold collision dynamics at long range.

DOI
10.1103/physreva.99.032710

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Interactions in a spin-polarized ultracold Fermi gas are governed by ppp-wave collisions and can be characterized by the ppp-wave scattering volume. Control of these collisions by Feshbach resonances is hampered by huge inelastic losses. Here, we suggest nonresonant light control of ppp-wave collisions, exploiting the anisotropic coupling of nonresonant light to the polarizability of the atoms. The ppp-wave scattering volume can be controlled by strong nonresonant light, in close analogy to the sss-wave scattering length. For collision partners that are tightly trapped, the nonresonant light induces an energy shift directly related to the scattering volume (as defined by A. Crubellier, R. Gonz'alez-F'erez, C. P. Koch, and E. Luc-Koenig, preceding paper, Phys. Rev. A 99, 032709 (2019). This effect could be used to climb the ladder of the trap. We also show that controlling the scattering volume implies control, at least roughly, over the orientation at short interatomic distances of the interparticle axis relative to the polarization direction of the light. Our proposal is based on an asymptotic model that explicitly accounts for the anisotropic dipole-dipole interaction which governs the ultracold collision dynamics at long range.
A pair of atoms interacts with nonresonant light via its anisotropic polarizability. This effect can be used to tune the scattering properties of the atoms. Although the light-atom interaction varies with interatomic separation as 1/R31/{R}^{3}1/R3, the effective sss-wave potential decreases more rapidly as 1/R41/{R}^{4}1/R4 such that the field-dressed scattering length can be determined without any formal difficulty. The scattering dynamics are essentially governed by the long-range part of the interatomic interaction and can thus be accurately described by an asymptotic model [A. Crubellier et al., New J. Phys. 17, 045020 (2015)]. Here we use the asymptotic model to determine the field-dressed scattering length from the sss-wave radial component of a particular threshold wave function. Applying our theory to the scattering of two strontium isotopes, we calculate the variation of the scattering length with the intensity of the nonresonant light. Moreover, we predict the intensities at which the scattering length becomes infinite for any pair of atoms.
The creation of a gas of ultracold polar molecules with a high phase space density brings new possibilities beyond experiments with ultracold atomic gases. In particular, long-range, anisotropic, and tunable dipole-dipole interactions open the way for novel quantum gases, with applications including strongly correlated many-body systems, and ultracold chemistry. This thesis will present the final steps to complete control over both internal and external degrees of freedom of the molecule which allows us to control, and even completely suppress, the chemical reactions between molecules. First, the control over internal states has been achieved through coherent state transfer to the ro-vibronic ground state and coherent manipulations of the hyperfine and rotational states with microwave radiation. Second, external degrees of freedom are controlled by loading the gas into an optical lattice. With the molecules loaded into a one-dimensional lattice, the orientation of the molecular collisions is controlled by manipulating both internal (hyperfine states) and external (motional states in the direction of tight confinement) degrees of freedom. Most striking is that by preparing the molecules all in the lowest band of the lattice in the same internal state, the molecular collisions can only occur in a side-by-side" orientation, where the chemical reaction rate is suppressed by the repulsive dipole-dipole interactions. The chemical reaction can be suppressed completely by further constraining the motion in the trap in a strong 3D lattice. Here we see lifetimes longer than 20 s, limited by o-resonant light scattering. Finally, the ac polarizability of the molecules is explored and controlled. The different rotational states of the molecule have different polarizabilities and will experience a different trapping force in both the optical dipole trap or lattice. We show that there is a magic angle" between the quantization axis and the polarization of the trapping laser at which the polarizabilities of two different rotational states can be matched, eliminating dephasing and allowing for coherent manipulations between rotational states.
The definition of the scattering volume for ppp-wave collisions needs to be generalized in the presence of dipolar interactions for which the potential decreases with the interparticle separation as 1/R31/{R}^{3}1/R3. Here, we propose a way to define the scattering volume characterizing the short-range interactions in odd-parity waves, by analyzing the ppp-wave component of the two-body threshold wave function. Our approach uses an asymptotic model and introduces explicitly the anisotropic dipole-dipole interaction, which governs the ultracold collision dynamics at long range. The short-range interactions, which are essential to describe threshold resonances, are taken into account by a single parameter related to the nodal structure of the wave functions at short distances.
We study a spin-polarized degenerate Fermi gas interacting via a p-wave Feshbach resonance in an optical lattice. The strong confinement available in this system allows us to realize one- and two-dimensional gases and, therefore, to restrict the asymptotic scattering states of atomic collisions. When aligning the atomic spins along (or perpendicular to) the axis of motion in a one-dimensional gas, scattering into channels with the projection of the angular momentum of /m/ = 1 (or m = 0) can be inhibited. In two and three dimensions, we observe the doublet structure of the p-wave Feshbach resonance. For both the one-dimensional and the two-dimensional gases, we find a shift of the position of the resonance with increasing confinement due to the change in collisional energy. In a three-dimensional optical lattice, the losses on the Feshbach resonance are completely suppressed.
Abstract Ultracold temperatures in dilute quantum gases opened the way to an exquisite control of matter at the quantum level. Here we focus on the control of ultracold atomic collisions using a laser to engineer their interactions at large interatomic distances. We show that the entrance channel of two colliding ultracold atoms can be coupled to a repulsive collisional channel by the laser light so that the overall interaction between the two atoms becomes repulsive: this prevents them to come close together and to undergo inelastic processes, thus protecting the atomic gases from unwanted losses. We illustrate such an optical shielding (OS) mechanism with 39 K and 133 Cs atoms colliding at ultracold temperature (<1 μK). The process is described in the framework of the dressed-state picture and we then solve the resulting stationary coupled Schrödinger equations. The role of spontaneous emission and photoinduced inelastic scattering is also investigated as possible limitations of the shielding efficiency. We predict an almost complete suppression of inelastic collisions over a broad range of Rabi frequencies and detunings from the 39 K D2 line of the OS laser, both within the [0, 200 MHz] interval. We found that the polarization of the shielding laser has a minor influence on this efficiency. This proposal could easily be formulated for other bialkali-metal pairs as their long-range interaction are all very similar to each other.
Using a recently developed approach for treating the three-dimensional anisotropic scattering we find considerable influence of a nonresonant laser field with intensity $I\ensuremath{\ge}{10}^{5}\text{ }\text{ }\mathrm{W}/{\mathrm{c}\mathrm{m}}^{2}$ on the Cs-Cs ultracold collisions. Strong dependence on the laser wavelength ${\ensuremath{\lambda}}_{L}$ is shown at the optical region as ${\ensuremath{\lambda}}_{L}$ becomes shorter than the critical value ${\ensuremath{\lambda}}_{0}\ensuremath{\sim}3000\text{ }\text{ }\mathrm{n}\mathrm{m}$ (of the atomic de Broglie wave $\ensuremath{\lambda}$) defining the region ${\ensuremath{\lambda}}_{0}\ensuremath{\le}\ensuremath{\lambda}$ of the sss-wave domination in the absence of the external field. Dependence on the laser polarization is also essential. The found effect can be applicable for controlling atom-atom interactions at ultralow temperatures.