Dicke superradiance in the field of a coherent phonon wave

Evgenii Dmitrievich Trifonov

Aranya B. Bhattacherjee, Tobias Brandes

We propose the possibility of a phonon laser by coupling a Bose–Einstein condensate to a nanomechanical cantilever with a magnetic tip. Due to the magnetic coupling, atomic spin flips induce cantilever motion, which can be used to produce a phonon laser. The system is described by the equivalent of the Jaynes–Cummings Hamiltonian. By controlling the number of atoms and the population inversion, one can obtain either a continuous wave or transient lasing. The two-body atom–atom interaction is also shown to coherently manipulate the lasing process. We also show that in the strong coupling limit, the same system can undergo a Dicke–Hepp–Lieb superradiant phase transition. Exotic phase diagrams can be obtained by tuning the two body atom–atom interaction.

Jörg Helge Müller, Dirk Witthaut, Rodolphe Le Targat +3 more

Due to its coherence properties and high optical depth, a Bose–Einstein condensate [BEC] provides an ideal setting to investigate collective atom-light interactions. Superradiant light scattering [SLS] in a BEC is a fascinating example of such an interaction. It is an analogous process to Dicke superradiance, in which an electronically inverted sample decays collectively, leading to the emission of one or more light pulses in a well-defined direction. Through time-resolved measurements of the superradiant light pulses emitted by an end-pumped BEC, we study the close connection of SLS with Dicke superradiance. A 1D model of the system yields good agreement with the experimental data and shows that the dynamics result from the structures that build up in the light and matter-wave fields along the BEC. This paves the way for exploiting the atom–photon correlations generated by the superradiance.

B. M. Pimentel, Abraham Hirsz Zimerman

Daniel Bhatti, Manuel Bojer, Joachim von Zanthier

Dicke superradiance, i.e., the enhanced spontaneous emission of coherent radiation, is often attributed to radiation emitted by synchronized dipoles coherently oscillating in phase. At the same time, Dicke derived superradiance assuming atoms in entangled Dicke states which do not display any dipole moment. To shed light on this apparent paradox, we study the intensity distribution arising from two identical two-level atoms prepared either in an entangled Dicke state or in a separable atomic state with a nonvanishing dipole moment. We find that the two configurations produce similar far-field intensity patterns, although they stem from fundamentally distinct types of coherence: while in the second case the atoms display coherence among the individual particles, leading to Young-type interference like that known from classical dipoles, atoms in Dicke states possess collective quantum coherence stemming from entanglement and quantum correlations of the state, leading to an interference pattern resulting from enhanced spontaneous emission. This demonstrates that the radiation generated by synchronized dipoles and Dicke superradiance---even if they do produce the same interference pattern---are fundamentally distinct phenomena and have to be interpreted in different ways.

Igor Ferrier-Barbut