139 research outputs found
Anharmonic parametric excitation in optical lattices
We study both experimentally and theoretically the losses induced by
parametric excitation in far-off-resonance optical lattices. The atoms confined
in a 1D sinusoidal lattice present an excitation spectrum and dynamics
substantially different from those expected for a harmonic potential. We
develop a model based on the actual atomic Hamiltonian in the lattice and we
introduce semiempirically a broadening of the width of lattice energy bands
which can physically arise from inhomogeneities and fluctuations of the
lattice, and also from atomic collisions. The position and strength of the
parametric resonances and the evolution of the number of trapped atoms are
satisfactorily described by our model.Comment: 7 pages, 5 figure
Collective Sideband Cooling in an Optical Ring Cavity
We propose a cavity based laser cooling and trapping scheme, providing tight
confinement and cooling to very low temperatures, without degradation at high
particle densities. A bidirectionally pumped ring cavity builds up a resonantly
enhanced optical standing wave which acts to confine polarizable particles in
deep potential wells. The particle localization yields a coupling of the
degenerate travelling wave modes via coherent photon redistribution. This
induces a splitting of the cavity resonances with a high frequency component,
that is tuned to the anti-Stokes Raman sideband of the particles oscillating in
the potential wells, yielding cooling due to excess anti-Stokes scattering.
Tight confinement in the optical lattice together with the prediction, that
more than 50% of the trapped particles can be cooled into the motional ground
state, promise high phase space densities.Comment: 4 pages, 1 figur
Effective Field Theory for Rydberg Polaritons
We develop an effective field theory (EFT) to describe the few- and many-body
propagation of one dimensional Rydberg polaritons. We show that the photonic
transmission through the Rydberg medium can be found by mapping the propagation
problem to a non-equilibrium quench, where the role of time and space are
reversed. We include effective range corrections in the EFT and show that they
dominate the dynamics near scattering resonances in the presence of deep bound
states. Finally, we show how the long-range nature of the Rydberg-Rydberg
interactions induces strong effective -body interactions between Rydberg
polaritons. These results pave the way towards studying non-perturbative
effects in quantum field theories using Rydberg polaritons.Comment: 5+ pages main text, 3 figures; 5 pages supplemental, 1 figure; v2 -
replaced discussion of N-body bound state preparation with discussion of
effective range corrections and made other minor correction
Cooling atoms in an optical trap by selective parametric excitation
We demonstrate the possibility of energy-selective removal of cold atoms from
a tight optical trap by means of parametric excitation of the trap vibrational
modes. Taking advantage of the anharmonicity of the trap potential, we
selectively remove the most energetic trapped atoms or excite those at the
bottom of the trap by tuning the parametric modulation frequency. This process,
which had been previously identified as a possible source of heating, also
appears to be a robust way for forcing evaporative cooling in anharmonic traps.Comment: 5 pages, 5 figure
Lasing and cooling in a hot cavity
We present a microscopic laser model for many atoms coupled to a single
cavity mode, including the light forces resulting from atom-field momentum
exchange. Within a semiclassical description, we solve the equations for atomic
motion and internal dynamics to obtain analytic expressions for the optical
potential and friction force seen by each atom. When optical gain is maximum at
frequencies where the light field extracts kinetic energy from the atomic
motion, the dynamics combines optical lasing and motional cooling. From the
corresponding momentum diffusion coefficient we predict sub-Doppler
temperatures in the stationary state. This generalizes the theory of cavity
enhanced laser cooling to active cavity systems. We identify the gain induced
reduction of the effective resonator linewidth as key origin for the faster
cooling and lower temperatures, which implys that a bad cavity with a gain
medium can replace a high-Q cavity. In addition, this shows the importance of
light forces for gas lasers in the low-temperature limit, where atoms can
arrange in a periodic pattern maximizing gain and counteracting spatial hole
burning. Ultimately, in the low temperature limit, such a setup should allow to
combine optical lasing and atom lasing in single device.Comment: 11 pages, 6 figure
Novel Ferromagnetic Atom Waveguide with in situ loading
Magneto-optic and magnetostatic trapping is realized near a surface using
current carrying coils wrapped around magnetizable cores. A cloud of 10^7
Cesium atoms is created with currents less than 50 mA. Ramping up the current
while maintaining optical dissipation leads to tightly confined atom clouds
with an aspect ratio of 1:1000. We study the 3D character of the magnetic
potential and characterize atom number and density as a function of the applied
current. The field gradient in the transverse dimension has been varied from <
10 G/cm to > 1 kG/cm. By loading and cooling atoms in-situ, we have eliminated
the problem of coupling from a MOT into a smaller phase space.Comment: 4 pages, 4 figure
Generating Entanglement and Squeezed States of Nuclear Spins in Quantum Dots
Entanglement generation and detection are two of the most sought-after goals
in the field of quantum control. Besides offering a means to probe some of the
most peculiar and fundamental aspects of quantum mechanics, entanglement in
many-body systems can be used as a tool to reduce fluctuations below the
standard quantum limit. For spins, or spin-like systems, such a reduction of
fluctuations can be realized with so-called squeezed states. Here we present a
scheme for achieving coherent spin squeezing of nuclear spin states in
few-electron quantum dots. This work represents a major shift from earlier
studies in quantum dots, which have explored classical "narrowing" of the
nuclear polarization distribution through feedback involving stochastic spin
flips. In contrast, we use the nuclear-polarization-dependence of the electron
spin resonance (ESR) to provide a non-linearity which generates a non-trivial,
area-preserving, "twisting" dynamics that squeezes and stretches the nuclear
spin Wigner distribution without the need for nuclear spin flips.Comment: 8 pgs, 3 fgs. References added, text update
Ion crystal transducer for strong coupling between single ions and single photons
A new approach for realization of a quantum interface between single photons
and single ions in an ion crystal is proposed and analyzed. In our approach the
coupling between a single photon and a single ion is enhanced via the
collective degrees of freedom of the ion crystal. Applications including
single-photon generation, a memory for a quantum repeater, and a deterministic
photon-photon, photon-phonon, or photon-ion entangler are discussed.Comment: 4 pages, 2 figures, minor improvements, published in Physical Review
Letter
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