Observation of a Red-Blue Detuning Asymmetry in Matter-Wave Superradiance

Abstract

We report the first experimental observations of strong suppression of matter-wave superradiance using blue-detuned pump light and demonstrate a pump-laser detuning asymmetry in the collective atomic recoil motion. In contrast to all previous theoretical frameworks, which predict that the process should be symmetric with respect to the sign of the pump-laser detuning, we find that for condensates the symmetry is broken. With high condensate densities and red-detuned light, the familiar distinctive multi-order, matter-wave scattering pattern is clearly visible, whereas with bluedetuned light superradiance is strongly suppressed. In the limit of a dilute atomic gas, however, symmetry is restored. [7][8][9][10][11][12][13][14][15][16] have studied this light/matter-wave interaction process that is of significant importance to the fields of cold atomic physics, cold molecular physics, nonlinear optics and quantum information science.The widely-accepted theory [1] of matter-wave superradiance is based on spontaneous Rayleigh scattering and the buildup of a matter-wave grating enhanced by subsequent stimulated Rayleigh scattering. This intuitive picture, which correctly models late-stage superradiant growth when red-detuned light is used, captures many important aspects of this intriguing matter-light interaction process. However, the simple grating viewpoint and most rate-equation-based theories neglect propagation dynamics of the internally-generated optical field. In fact, the initial study [1] explicitly assumed that the optical fields traveled at the speed of light in vacuum and therefore did not affect scattering at later times. To date, no report in the literature has contradicted that statement [17]. However, we have recently shown theoretically [18,19] that the internally-generated field propagates ultra slowly and plays an important role in the genesis of superradiance with BECs. We also note that most previous theories effectively treated the BEC as a thermal gas by neglecting the extra factor of the mean-field potential seen by the scattered atoms due to the exchange term in the Hamiltonian. As we will show, this unique property of BECs profoundly impacts superradiant scattering and leads to the pump detuning asymmetry reported here.In this Letter we present the first experimental ob- servation of a red-blue detuning asymmetry in matterwave superradiance. We demonstrate astonishingly efficient suppression of superradiance when the pump laser is blue detuned that cannot be explained by current theoretical frameworks. However, using our new theoretical framework [18] we propose a possible explanation for the detuning asymmetry based on an induced optical-dipole potential that results from the ultra-slow propagation velocity and gain characteristics of the generated field. The experimental data reported here were obtained using two 87 Rb BECs created with very different experi-

Second-order coherence of superradiance from a Bose-Einstein condensate

“…and, as a result, a complex nomenclature has evolved including the terms superradiance, superfluorescence, amplified spontaneous emission, mirrorless lasing, and random lasing [2, 4,[6][7][8][9], the distinctions among which we will not attempt to summarize here. The problem has recently seen renewed interest in the field of cold atoms [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. This is partly because cold atoms provide a reproducible, easily characterized ensemble in which Doppler broadening effects are small and relaxation is generally limited to spontaneous emission.…”

Quantum Phase Transition of Bose Einstein Condensation in Optical Cavity with Nonlinear Interaction

“…The quantum phase transition (QPT) [20] from the normal phase to the superradiance phase in BECs-cavity system has been observed experimentally [21][22][23]. In the experiment [23], the two-level atoms induce a sufficiently strong coupling between the transverse pump light and the cavity field, which is a nonlinear interaction and the system undergoes a phase transition when tuning the power of the transverse pump light.…”

Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion

“…In this situation, the wave-function of the ground state shall take the Thomas-Fermi form in mean-field approximation because of the presence of the atomic interactions. The superradiance of such symmetric BEC has been studied [1][2][3][4][5][6][7][8][9]; however, research of that for the asymmetric BEC as that shown in Fig. 2(a) has been lack.…”

“…Ever since the first observation of superradiant scattering from the BEC, a series of experiments [1][2][3][4][5][6][7][8][9] have been explored to simulate the origin of this phenomenon and the dynamical properties of the light-atom coupling process. Experiments of different geometries, such as the Rayleigh and Raman superradiant scattering, in which the lights are pumped in the axial or radial direction [10,11] were intensively studied.…”