261 research outputs found

### All-optical transport and compression of ytterbium atoms into the surface of a solid immersion lens

We present an all-optical method to load 174Yb atoms into a single layer of
an optical trap near the surface of a solid immersion lens which improves the
numerical aperture of a microscope system. Atoms are transported to a region 20
um below the surface using a system comprised by three optical dipole traps.
The "optical accordion" technique is used to create a condensate and compress
the atoms to a width of 120 nm and a distance of 1.8 um away from the surface.
Moreover, we are able to verify that after compression the condensate behaves
as a two-dimensional quantum gas.Comment: 5 pages, 5 figure

### Entanglement of orbital angular momentum states between an ensemble of cold atoms and a photon

Recently, atomic ensemble and single photons were successfully entangled by
using collective enhancement [D. N. Matsukevich, \textit{et al.}, Phys. Rev.
Lett. \textbf{95}, 040405(2005).], where atomic internal states and photonic
polarization states were correlated in nonlocal manner. Here we experimentally
clarified that in an ensemble of atoms and a photon system, there also exists
an entanglement concerned with spatial degrees of freedom. Generation of
higher-dimensional entanglement between remote atomic ensemble and an
application to condensed matter physics are also discussed.Comment: 5 pages, 3 figure

### Quantum effects in the collective light scattering by coherent atomic recoil in a Bose-Einstein condensate

We extend the semiclassical model of the collective atomic recoil laser
(CARL) to include the quantum mechanical description of the center-of-mass
motion of the atoms in a Bose-Einstein condensate (BEC). We show that when the
average atomic momentum is less than the recoil momentum $\hbar\vec q$, the
CARL equations reduce to the Maxwell-Bloch equations for two momentum levels.
In the conservative regime (no radiation losses), the quantum model depends on
a single collective parameter, $\rho$, that can be interpreted as the average
number of photons scattered per atom in the classical limit. When $\rho\gg 1$,
the semiclassical CARL regime is recovered, with many momentum levels populated
at saturation. On the contrary, when $\rho\le 1$, the average momentum
oscillates between zero and $\hbar\vec q$, and a periodic train of $2\pi$
hyperbolic secant pulses is emitted. In the dissipative regime (large radiation
losses) and in a suitable quantum limit, a sequential superfluorescence
scattering occurs, in which after each process atoms emit a $\pi$ hyperbolic
secant pulse and populate a lower momentum state. These results describe the
regular arrangement of the momentum pattern observed in recent experiments of
superradiant Rayleigh scattering from a BEC.Comment: submitted for publication on Phys. Rev.

### Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate

We construct a Mach-Zehnder interferometer using Bose-Einstein condensed
rubidium atoms and optical Bragg diffraction. In contrast to interferometers
based on normal diffraction, where only a small percentage of the atoms
contribute to the signal, our Bragg diffraction interferometer uses all the
condensate atoms. The condensate coherence properties and high phase-space
density result in an interference pattern of nearly 100% contrast. In
principle, the enclosed area of the interferometer may be arbitrarily large,
making it an ideal tool that could be used in the detection of vortices, or
possibly even gravitational waves.Comment: 10 pages, 3 figures, Quantum Electronics and Laser Science Conference
1999, Postdeadline papers QPD12-

### Does matter wave amplification work for fermions?

We discuss the relationship between bosonic stimulation, density
fluctuations, and matter wave gratings. It is shown that enhanced stimulated
scattering, matter wave amplification and atomic four-wave mixing are in
principle possible for fermionic or non-degenerate samples if they are prepared
in a cooperative state. In practice, there are limitations by short coherence
times.Comment: 5 pages, 1 figure

### Spontaneous emission of atoms via collisions of Bose-Einstein condensates

The widely used Gross-Pitaevskii equation treats only coherent aspects of the
evolution of a Bose-Einstein condensate. However, inevitably some atoms scatter
out of the condensate. We have developed a method, based on the field theory
formulation, describing the dynamics of incoherent processes which are due to
elastic collisions. We can therefore treat processes of spontaneous emission of
atoms into the empty modes, as opposed to stimulated processes, which require
non-zero initial occupation.
In this article we study two counter-propagating plane waves of atoms,
calculating the full dynamics of mode occupation, as well as the statistics of
scattered atoms. The more realistic case of Gaussian wavepackets is also
analyzed.Comment: 5 pages, 2 figure

### Sequential superradiant scattering from atomic Bose-Einstein condensates

We theoretically discuss several aspects of sequential superradiant
scattering from atomic Bose-Einstein condensates. Our treatment is based on the
semiclassical description of the process in terms of the Maxwell-Schroedinger
equations for the coupled matter-wave and optical fields. First, we investigate
sequential scattering in the weak-pulse regime and work out the essential
mechanisms responsible for bringing about the characteristic fan-shaped
side-mode distribution patterns. Second, we discuss the transition between the
Kapitza-Dirac and Bragg regimes of sequential scattering in the strong-pulse
regime. Finally, we consider the situation where superradiance is initiated by
coherently populating an atomic side mode through Bragg diffraction, as in
studies of matter-wave amplification, and describe the effect on the sequential
scattering process.Comment: 9 pages, 4 figures. Submitted to Proceedings of LPHYS'06 worksho

### Measuring Qutrit-Qutrit Entanglement of Orbital Angular Momentum States of an Atomic Ensemble and a Photon

Three-dimensional entanglement of orbital angular momentum states of an
atomic qutrit and a single photon qutrit has been observed. Their full state
was reconstructed using quantum state tomography. The fidelity to the maximally
entangled state of Schmidt rank 3 exceeds the threshold 2/3. This result
confirms that the density matrix cannot be decomposed into ensemble of pure
states of Schmidt rank 1 or 2. That is, the Schmidt number of the density
matrix must be equal to or greater than 3.Comment: 5 pages, 4 figure

### Faraday Rotation with Single Nuclear Spin Qubit in a High-Finesse Optical Cavity

When an off-resonant light field is coupled with atomic spins, its
polarization can rotate depending on the direction of the spins via a Faraday
rotation which has been used for monitoring and controlling the atomic spins.
We observed Faraday rotation by an angle of more than 10 degrees for a single
1/2 nuclear spin of 171Yb atom in a high-finesse optical cavity. By employing
the coupling between the single nuclear spin and a photon, we have also
demonstrated that the spin can be projected or weakly measured through the
projection of the transmitted single ancillary photon.Comment: 6 pages, 6 figure

### Storage and Retrieval of a Squeezed Vacuum

Storage and retrieval of a squeezed vacuum was successfully demonstrated
using electromagnetically induced transparency. 930ns of the squeezed vacuum
pulse was incident on the laser cooled 87Rb atoms with an intense control light
in a coherent state. When the squeezed vacuum pulse was slowed and spatially
compressed in the cold atoms, the control light was switched off. After 3us of
storage, the control light was switched on again and the squeezed vacuum was
retrieved, as was confirmed using the time-domain homodyne method.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

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