136 research outputs found
Tunneling of ultracold atoms in time-independent potentials
We present theoretical as well as experimental results on resonantly enhanced
quantum tunneling of Bose-Einstein condensates in optical lattices both in the
linear case of single particle dynamics and in the presence of atom-atom
interactions. Our results demonstrate the usefulness of condensates in optical
lattices for the dynamical control of tunneling and for simulating Hamiltonians
originally used for describing solid state phenomena.Comment: slightly amended version published as ch. 11 of a book edited by S.
Keshavamurthy and P. Schlagheck with the title "Dynamical Tunneling: Theory
and Experiment
Bose-Einstein condensates in 1D optical lattices: nonlinearity and Wannier-Stark spectra
We present our experimental investigations on the subject of
nonlinearity-modified Bloch-oscillations and of nonlinear Landau-Zener
tunneling between two energy bands in a rubidium Bose Einstein condensate in an
accelerated periodic potential. Nonlinearity introduces an asymmetry in
Landau-Zener tunneling. We also present measurements of resonantly enhanced
tunneling between the Wannier-Stark energy levels for Bose-Einstein condensates
loaded into an optical lattice.Comment: Chapter of "Nonlinearities of Periodic Structures and Metamaterials"
(edited by C. Denz, S. Flach, and Yu. Kivshar) to be published by Springe
Two-photon and EIT-assisted Doppler cooling in a three-level cascade system
Laser cooling is theoretically investigated in a cascade three-level scheme,
where the excited state of a laser-driven transition is coupled by a second
laser to a top, more stable level, as for alkali-earth atoms. The second laser
action modifies the atomic scattering cross section and produces temperatures
lower than those reached by Doppler cooling on the lower transition. When
multiphoton processes due to the second laser are relevant, an electromagnetic
induced transparency modifies the absorption of the first laser, and the final
temperature is controlled by the second laser parameters. When the intermediate
state is only virtually excited, the dynamics is dominated by the two-photon
process and the final temperature is determined by the spontaneous decay rate
of the top state.Comment: 5 pages, 3 figures. Revised version, accepted for publication in
Phys. Rev A (Rapid Comm.
Four-level N-scheme crossover resonances in Rb saturation spectroscopy in magnetic fields
We perform saturated absorption spectroscopy on the D line for room
temperature rubidium atoms immersed in magnetic fields within the 0.05-0.13 T
range. At those medium-high field values the hyperfine structure in the excited
state is broken by the Zeeman effect, while in the ground state hyperfine
structure and Zeeman shifts are comparable. The observed spectra are composed
by a large number of absorption lines. We identify them as saturated
absorptions on two-level systems, on three-level systems in a V configuration
and on four-level systems in a N or double-N configuration where two optical
transitions not sharing a common level are coupled by spontaneous emission
decays. We analyze the intensity of all those transitions within a unified
simple theoretical model. We concentrate our attention on the double-N
crossovers signals whose intensity is very large because of the symmetry in the
branching ratios of the four levels. We point out that these structures,
present in all alkali atoms at medium-high magnetic fields, have interesting
properties for electromagnetically induced transparency and slow light
applications.Comment: Submitted to Physical Review
Bright and dark Autler-Townes states in the atomic Rydberg multilevel spectroscopy
We investigated the Autler-Townes (AT) splitting produced by microwave (mw) transitions between atomic Rydberg states explored by optical spectroscopy from the ground electronic state. The laser-atom Hamiltonian describing the double irradiation of such a multilevel system is analysed on the basis of the Morris-Shore transformation. The application of this transformation to the mw-dressed atomic system allows the identification of bright, dark, and spectator states associated with different configurations of atomic states and mw polarisations. We derived synthetic spectra that show the main features of Rydberg spectroscopy. Complex AT spectra are obtained in a regime of strong mw dressing, where a hybridisation of the Rydberg fine structure states is produced by the driving
Probe light-shift elimination in Generalized Hyper-Ramsey quantum clocks
We present a new interrogation scheme for the next generation of quantum
clocks to suppress frequency-shifts induced by laser probing fields themselves
based on Generalized Hyper-Ramsey resonances. Sequences of composite laser
pulses with specific selection of phases, frequency detunings and durations are
combined to generate a very efficient and robust frequency locking signal with
almost a perfect elimination of the light-shift from off resonant states and to
decouple the unperturbed frequency measurement from the laser's intensity. The
frequency lock point generated from synthesized error signals using either
or laser phase-steps during the intermediate pulse is tightly
protected against large laser pulse area variations and errors in potentially
applied frequency shift compensations. Quantum clocks based on weakly allowed
or completely forbidden optical transitions in atoms, ions, molecules and
nuclei will benefit from these hyper-stable laser frequency stabilization
schemes to reach relative accuracies below the 10 level.Comment: accepted for publication in Phys. Rev.
Magic radio-frequency dressing of nuclear spins in high-accuracy optical clocks
A Zeeman-insensitive optical clock atomic transition is engineered when
nuclear spins are dressed by a non resonant radio-frequency field. For
fermionic species as Sr, Yb, and Hg, particular ratios
between the radiofrequency driving amplitude and frequency lead to "magic"
magnetic values where a net cancelation of the Zeeman clock shift and a
complete reduction of first order magnetic variations are produced within a
relative uncertainty below the level. An Autler-Townes continued
fraction describing a semi-classical radio-frequency dressed spin is
numerically computed and compared to an analytical quantum description
including higher order magnetic field corrections to the dressed energies.Comment: accepted for publication in Phys. Rev. Let
Coherent transport of cold atoms in angle-tuned optical lattices
Optical lattices with a large spacing between the minima of the optical
potential can be created using the angle-tuned geometry where the 1-D periodic
potential is generated by two propagating laser beams intersecting at an angle
different from . The present work analyzes the coherent transport for the
case of this geometry. We show that the potential depth can be kept constant
during the transport by choosing a magic value for the laser wavelength. This
value agrees with that of the counterpropagating laser case, and the magic
wavelength does not depend of the optical lattice geometry. Moreover, we find
that this scheme can be used to implement controlled collision experiments
under special geometric conditions. Finally we study the transport of
hyperfine-Zeeman states of rubidium 87.Comment: 8 pages, 5 figures, one section added, in press in Phys. Rev.
Ultracold Rubidium atoms excited to Rydberg levels
Ultracold atomic gases excited to strongly interacting Rydberg states are a promising system for quantum simulations of many-body systems. The dipole blockade of Rydberg excitations is a hallmark of the strong interactions between atoms in these high-lying quantum states. We have measured the Rydberg excitation for rubidium ultracold atoms in magneto-optical traps and for Bose-Einstein condensates loaded into quasi one-dimensional traps. One of the consequences of the dipole blockade is the suppression of fluctuations in the counting statistics of Rydberg excitations. We have obtained experimental results on the dynamics and the counting statistics of Rydberg excitations of ultra-cold Rubidium atoms both on and off resonance, which exhibit sub- and super-Poissonian counting statistics, respectively. We have found strongly bimodal counting distributions in the offresonant regime
Unearthing wave-function renormalization effects in the time evolution of a Bose-Einstein condensate
We study the time evolution of a Bose-Einstein condensate in an accelerated
optical lattice. When the condensate has a narrow quasimomentum distribution
and the optical lattice is shallow, the survival probability in the ground band
exhibits a steplike structure. In this regime we establish a connection between
the wave-function renormalization parameter and the phenomenon of
resonantly enhanced tunneling.Comment: 12 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1201.628
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