4 research outputs found
Quantum Optics with Quantum Gases
Quantum optics with quantum gases represents a new field, where the quantum
nature of both light and ultracold matter plays equally important role. Only
very recently this ultimate quantum limit of light-matter interaction became
feasible experimentally. In traditional quantum optics, the cold atoms are
considered classically, whereas, in quantum atom optics, the light is used as
an essentially classical axillary tool. On the one hand, the quantization of
optical trapping potentials can significantly modify many-body dynamics of
atoms, which is well-known only for classical potentials. On the other hand,
atomic fluctuations can modify the properties of the scattered light.Comment: to be published in Laser Physics (2009
Bright and dark excitons in an atom--pair filled optical lattice within a cavity
We study electronic excitations of a degenerate gas of atoms trapped in pairs
in an optical lattice. Local dipole-dipole interactions produce a long lived
antisymmetric and a short lived symmetric superposition of individual atomic
excitations as the lowest internal on-site excitations. Due to the much larger
dipole moment the symmetric states couple efficiently to neighbouring lattice
sites and can be well represented by Frenkel excitons, while the antisymmetric
dark states stay localized. Within a cavity only symmetric states couple to
cavity photons inducing long range interactions to form polaritons. We
calculate their dispersion curves as well as cavity transmission and reflection
spectra to observe them. For a lattice with aspherical sites bright and dark
states get mixed and their relative excitation energies depend on photon
polarizations. The system should allow to study new types of solid state
phenomena in atom filled optical lattices
Ultracold atoms in optical lattices generated by quantized light fields
We study an ultracold gas of neutral atoms subject to the periodic optical
potential generated by a high- cavity mode. In the limit of very low
temperatures, cavity field and atomic dynamics require a quantum description.
Starting from a cavity QED single atom Hamiltonian we use different routes to
derive approximative multiparticle Hamiltonians in Bose-Hubbard form with
rescaled or even dynamical parameters. In the limit of large enough cavity
damping the different models agree. Compared to free space optical lattices,
quantum uncertainties of the potential and the possibility of atom-field
entanglement lead to modified phase transition characteristics, the appearance
of new phases or even quantum superpositions of different phases. Using a
corresponding effective master equation, which can be numerically solved for
few particles, we can study time evolution including dissipation. As an example
we exhibit the microscopic processes behind the transition dynamics from a Mott
insulator like state to a self-ordered superradiant state of the atoms, which
appears as steady state for transverse atomic pumping.Comment: 17 pages, 10 figures, Published versio
Quantum stability of self-organized atomic insulator-like states in optical resonators
We investigate a paradigm example of cavity quantum electrodynamics with many
body systems: an ultracold atomic gas inside a pumped optical resonator. In
particular, we study the stability of atomic insulator-like states, confined by
the mechanical potential emerging from the cavity field spatial mode structure.
As in open space, when the optical potential is sufficiently deep, the atomic
gas is in the Mott-like state. Inside the cavity, however, the potential
depends on the atomic distribution, which determines the refractive index of
the medium, thus altering the intracavity field amplitude. We derive the
effective Bose-Hubbard model describing the physics of the system in one
dimension and study the crossover between the superfluid -- Mott insulator
quantum states. We determine the regions of parameters where the atomic
insulator states are stable, and predict the existence of overlapping stability
regions corresponding to competing insulator-like states. Bistable behavior,
controlled by the pump intensity, is encountered in the vicinity of the shifted
cavity resonance.Comment: 13 pages, 6 figures. Replaced with revised version. Accepted for
publication in New J. Phys., special issue "Quantum correlations in tailord
matter