Showing papers by "Sylvain Nascimbene published in 2018"

Sound Propagation in a Uniform Superfluid Two-Dimensional Bose Gas.

Abstract: In superfluid systems several sound modes can be excited, such as, for example, first and second sound in liquid helium. Here, we excite running and standing waves in a uniform two-dimensional Bose gas and we characterize the propagation of sound in both the superfluid and normal regimes. In the superfluid phase, the measured speed of sound is in good agreement with the prediction of a two-fluid hydrodynamic model, and the weak damping is well explained by the scattering with thermal excitations. In the normal phase we observe a stronger damping, which we attribute to a departure from hydrodynamic behavior.

Quantum-enhanced sensing using non-classical spin states of a highly magnetic atom.

Abstract: Coherent superposition states of a mesoscopic quantum object play a major role in our understanding of the quantum to classical boundary, as well as in quantum-enhanced metrology and computing. However, their practical realization and manipulation remains challenging, requiring a high degree of control of the system and its coupling to the environment. Here, we use dysprosium atoms—the most magnetic element in its ground state—to realize coherent superpositions between electronic spin states of opposite orientation, with a mesoscopic spin size J = 8. We drive coherent spin states to quantum superpositions using non-linear light-spin interactions, observing a series of collapses and revivals of quantum coherence. These states feature highly non-classical behavior, with a sensitivity to magnetic fields enhanced by a factor 13.9(1.1) compared to coherent spin states—close to the Heisenberg limit 2J = 16—and an intrinsic fragility to environmental noise. Moderate-size coherent superpositions of spin states allow quantum enhancements in metrology. Here, the authors exploit the large electronic spin of dysprosium atoms to realize mesoscopic spin superpositions, allowing a 14-fold quantum enhancement in magnetic field sensitivity, close to the Heisenberg limit.

Quantum-enhanced sensing using non-classical spin states of a highly magnetic atom

Abstract: Coherent superposition states of a mesoscopic quantum object play a major role in our understanding of the quantum to classical boundary, as well as in quantum-enhanced metrology and computing. However, their practical realization and manipulation remains challenging, requiring a high degree of control of the system and its coupling to the environment. Here, we use dysprosium atoms - the most magnetic element in its ground state - to realize coherent superpositions between electronic spin states of opposite orientation, with a mesoscopic spin size J=8. We drive coherent spin states to quantum superpositions using non-linear light-spin interactions, observing a series of collapses and revivals of quantum coherence. These states feature highly non-classical behavior, with a sensitivity to magnetic fields enhanced by a factor 13.9(1.1) compared to coherent spin states - close to the Heisenberg limit 2J=16 - and an intrinsic fragility to environmental noise.

Resonant-light diffusion in a disordered atomic layer

Abstract: Light scattering in dense media is a fundamental problem of many-body physics, which is also relevant for the development of optical devices. In this work we investigate experimentally light propagation in a dense sample of randomly positioned resonant scatterers confined in a layer of subwavelength thickness. We locally illuminate the atomic cloud and monitor spatially resolved fluorescence away from the excitation region. We show that light spreading is well described by a diffusion process, involving many scattering events in the dense regime. For light detuned from resonance we find evidence that the atomic layer behaves as a graded-index planar waveguide. These features are reproduced by a simple geometrical model and numerical simulations of coupled dipoles.

Anisotropic light shift and magic polarization of the intercombination line of dysprosium atoms in a far-detuned dipole trap

Abstract: We characterize the anisotropic differential ac-Stark shift for the Dy $626\phantom{\rule{3.33333pt}{0ex}}\mathrm{nm}$ intercombination transition, induced in a far-detuned $1070\phantom{\rule{3.33333pt}{0ex}}\mathrm{nm}$ optical dipole trap, and observe the existence of a ``magic polarization'' for which the polarizabilities of the ground and excited states are equal. From our measurements we extract both the scalar and tensorial components of the dynamic dipole polarizability for the excited state, ${\ensuremath{\alpha}}_{E}^{\text{s}}=188(12){\ensuremath{\alpha}}_{\text{0}}$ and ${\ensuremath{\alpha}}_{E}^{\text{t}}=34(12){\ensuremath{\alpha}}_{\text{0}}$, respectively, where ${\ensuremath{\alpha}}_{\text{0}}$ is the atomic unit for the electric polarizability. We also provide a theoretical model allowing us to predict the excited state polarizability and find qualitative agreement with our observations. Furthermore, we utilize our findings to optimize the efficiency of Doppler cooling of a trapped gas, by controlling the sign and magnitude of the inhomogeneous broadening of the optical transition. The resulting initial gain of the collisional rate allows us, after forced evaporation cooling, to produce a quasipure Bose-Einstein condensate of $^{162}\mathrm{Dy}$ with $3\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms.