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Register a new userOptical control of the density and spin spatial profiles of a planar Bose gas
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We demonstrate the arbitrary control of the density profile of a two-dimensional Bose gas by shaping the optical potential applied to the atoms. We use a digital micromirror device (DMD) directly imaged onto the atomic cloud through a high resolution imaging system. Our approach relies on averaging the response of many pixels of the DMD over the diffraction spot of the imaging system, which allows us to create an optical potential with arbitrary grey levels and with micron-scale resolution. The obtained density distribution is optimized with a feedback loop based on the measured absorption images of the cloud. Using the same device, we also engineer arbitrary spin distributions thanks to a two-photon Raman transfer between internal ground states.
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Tans contact is a quantity that unifies many different properties of a low-temperature gas with short-range interactions, from its momentum distribution to its spatial two-body correlation function. Here, we use a Ramsey interferometric method to realize experimentally the thermodynamic definition of the two-body contact, i.e. the change of the internal energy in a small modification of the scattering length. Our measurements are performed on a uniform two-dimensional Bose gas of $^{87}$Rb atoms across the Berezinskii-Kosterlitz-Thouless superfluid transition. They connect well to the theoretical predictions in the limiting cases of a strongly degenerate fluid and of a normal gas. They also provide the variation of this key quantity in the critical region, where further theoretical efforts are needed to account for our findings.
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In atomic systems, clock states feature a zero projection of the total angular momentum and thus a low sensitivity to magnetic fields. This makes them widely used for metrological applications like atomic fountains or gravimeters. Here, we show that a mixture of two such non-magnetic states still display magnetic dipole-dipole interactions. Using high resolution spectroscopy of a planar gas of $^{87}$Rb atoms with a controlled in-plane shape, we explore the effective isotropic and extensive character of these interactions and demonstrate their tunability. Our measurements set strong constraints on the relative values of the s-wave scattering lengths $a_{ij}$ involving the two clock states.
We discuss the superfluid properties of a Bose-Einstein condensed gas with spin-orbit coupling, recently realized in experiments. We find a finite normal fluid density $rho_n$ at zero temperature which turns out to be a function of the Raman coupling. In particular, the entire fluid becomes normal at the transition point from the zero momentum to the plane wave phase, even though the condensate fraction remains finite. We emphasize the crucial role played by the gapped branch of the elementary excitations and discuss its contributions to various sum rules. Finally, we prove that an independent definition of superfluid density $rho_s$, using the phase twist method, satisfies the equality $rho_n+rho_s=rho$, the total density, despite the breaking of Galilean invariance.
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