Designer Spatial Control of Interactions in Ultracold Gases

Abstract

Designer optical control of interactions in ultracold atomic gases has wide application, from creating new quantum phases to modeling the physics of black holes. We demonstrate spatial control of interactions in a two-component cloud of 6 Li fermions, using electromagnetically induced transparency (EIT) to create a "sandwich" of resonantly and weakly interacting regions. Interaction designs are imprinted on the trapped cloud by two laser beams and manipulated with just MHz changes in the frequency of one beam. We employ radio-frequency spectroscopy to measure the imprinted 1D spatial profiles of the local mean-field interactions and to demonstrate that the tuning range of the scattering length is the same for both optical and magnetic control. All of the data are in excellent agreement with our continuum-dressed state theoretical model of optical control, which includes both the spatial and momentum dependence of the interactions. PACS numbers:Tunability of interactions in ultracold atomic gases has been achieved by exploiting magnetically controlled collisional (Feshbach) resonances [1], where the total energy of two colliding atoms in an energetically open channel is tuned into resonance with a bound dimer state in a closed channel. Optical field control offers a much richer palate, by creating designer interactions with high resolution in position, energy, momentum, and time. These techniques enable new paradigms. For example, energy resolution will provide better models of neutron matter by controlling the effective range [2, 6], while momentum resolution will permit non-zero momentum pairing in two component Fermi gases, i.e., synthetic FFLO states [4, 5]. The increased temporal resolution enables studies of nonequilibrium thermodynamics of strongly interacting gases on time scales faster than the Fermi time [6]. Spatial manipulation of interactions can be utilized to study controllable soliton emission [7], exotic quantum phases [8], long-living Bloch oscillations of matter waves [9], the physics of Hawking radiation from black holes [10], and scale-invariant dimer pairing [11]. However, optical techniques generally suffer from atom loss and heating due to spontaneous scattering, which severely limits their applicability [12][13][14][15][16][17][18][19][20].In a major breakthrough for suppressing spontaneous scattering, Bauer et al., [18] used a bound-to-bound transition in the closed channel, which is far away from the atomic resonance. To further suppress atom loss, large detunings on the bound-bound transition were employed. The large detunings limited the tunability of the scattering length a to ∆a ≃ 2 a bg , where a bg is the background scattering length. In addition, interactions were tuned by changing the intensity of the laser light, which changes the net external potential experienced by the atoms. Recently, Clark and coworkers [20] avoided this problem by using a "magic" wavelength, tuned in between D1 and D2 lines of 137 Cs atoms, to suppress the atomic polarizability and hence the change in the ...

Reservoir engineering of Cooper-pair-assisted transport with cold atoms

“…If this is not the case, a possible solution consists in increasing γ ℓ , which implies increasing the junction and transverse frequencies ω and ω ⊥ . We finally note that tuning the interaction U locally inside the junction using optically-induced Feshbach resonances as realised in [34] provides a good route to control over interactions with strongly reduced spontaneous scattering of photons, in a form that would be appropriate for the proposed setup.…”

“…The corresponding potential geometry could be achieved as proposed in [31] by using two laser beams with adjusted detunings, beam waists, and positions, but also more generally with acousto-optical deflectors [32] or holographic mask techniques [33]. The interaction U between atoms in the junction can for its part be tuned locally via optically-induced Feshbach resonances [34].…”

“…Here we address the details of the proposed experimental implementation and observation of the phenomena we discuss in this manuscript. We give examples of parameters currently available in experiments, basing values on 6 Li atoms following [1,4,21,34], and retain ÿ and k B in our expressions within this section.…”

Generalized Crossover in Interacting Fermions within the Low-Energy Expansion

“…In addition, we show that the solution for T c disappears in the large-positive-effective-range region with finite positive scattering length due to the breakdown of the effective range expansion at r e > a/2. Since an independent optical control of the scattering length and the effective range can be achieved in ultracold atomic gases [52][53][54][55][56][57], one can expect that our results can be checked by future experiments.…”

Hydrodynamics with spacetime-dependent scattering length

“…Here the quantum statistics of particles is controlled by the choice of atomic isotopes and dimensionality of space by the application of optical lattices [3]. In addition, an interparticle interaction is not only tunable in its magnitude and sign with the magnetic field via Feshbach resonances [6], but also variable over space and time at will to a reasonable extent [7][8][9]. While such a spacetime-dependent scattering length has been proposed to realize a number of intrigu-ing phenomena [10][11][12][13][14][15][16][17][18][19][20], it may also be useful as a novel probe of target systems.…”