Bose-Einstein condensation of stationary-light polaritons

We propose and analyze a mechanism for Bose-Einstein condensation of stationary dark-state polaritons. Dark-state polaritons (DSPs) are formed in the interaction of light with laser-driven 3-level Lambda-type atoms and are the basis of phenomena such as electromagnetically induced transparency (EIT), ultra-slow and stored light. They have long intrinsic lifetimes and in a stationary set-up with two counterpropagating control fields of equal intensity have a 3D quadratic dispersion profile with variable effective mass. Since DSPs are bosons they can undergo a Bose-Einstein condensation at a critical temperature which can be many orders of magnitude larger than that of atoms. We show that thermalization of polaritons can occur via elastic collisions mediated by a resonantly enhanced optical Kerr nonlinearity on a time scale short compared to the decay time. Finally condensation can be observed by turning stationary into propagating polaritons and monitoring the emitted light.Comment: 4 pages, 3 figure

Entanglement generation by adiabatic navigation in the space of symmetric multi-particle states

We propose a technique for robust and efficient navigation in the Hilbert space of entangled symmetric states of a multiparticle system with externally controllable linear and nonlinear collective interactions. A linearly changing external field applied along the quantization axis creates a network of well separated level crossings in the energy diagram of the collective states. One or more transverse pulsed fields applied at the times of specific level crossings induce adiabatic passage between these states. By choosing the timing of the pulsed field appropriately, one can transfer an initial product state of all N spins into (i) any symmetric state with n spin excitations and (ii) the N-particle analog of the Greenberger-Horne-Zeilinger state. This technique, unlike techniques using pulses of specific area, does not require precise knowledge of the number of particles and is robust against variations in the interaction parameters. We discuss potential applications in two-component Bose condensates and ion-trap systems.Comment: 7 pages, 6 figure

Excitation of strongly interacting moving Rydberg atoms by photon recoil momentum

Based on the fact that an ensemble of moving Rydberg atoms in two counterpropagating laser beams in the limit of complete dipole blocking is isomorphic to a Jaynes–Cummings model, a scheme for robust and efficient excitation of atomic Rydberg states is proposed. It is shown that the Doppler frequency shifts play an important role in atomic population transfer processes. The suggested method can be employed to detect the symmetric entangled states and paves the way to preparing entangled states with a single excited atom in a Rydberg state. It is shown that this process is robust with respect to parameter fluctuations, such as the laser pulse area, the relative spatial offset (the delay) of the laser beams and the number of atoms