297 research outputs found
Highly anisotropic Bose-Einstein condensates: crossover to lower dimensionality
We develop a simple analytical model based on a variational method to explain
the properties of trapped cylindrically symmetric Bose-Einstein condensates
(BEC) of varying degrees of anisotropy well into regimes of effective one
dimension (1D) and effective two dimension (2D). Our results are accurate in
regimes where the Thomas-Fermi approximation breaks down and they are shown to
be in agreement with recent experimental data.Comment: 4 pages, 2 figures; significantly more new material added; title and
author-list changed due to changes in conten
Dynamics of Macroscopic Wave Packet Passing through Double Slits: Role of Gravity and Nonlinearity
Using the nonlinear Schroedinger equation (Gross-Pitaevskii equation), the
dynamics of a macroscopic wave packet for Bose-Einstein condensates falling
through double slits is analyzed. This problem is identified with a search for
the fate of a soliton showing a head-on collision with a hard-walled obstacle
of finite size. We explore the splitting of the wave packet and its
reorganization to form an interference pattern. Particular attention is paid to
the role of gravity (g) and repulsive nonlinearity (u_0) in the fringe pattern.
The peak-to-peak distance in the fringe pattern and the number of interference
peaks are found to be proportional to g^(-1/2) and u_0^(1/2)g^(1/4),
respectively. We suggest a way of designing an experiment under controlled
gravity and nonlinearity.Comment: 10 pages, 4 figures and 1 tabl
Propagation of Bose-Einstein condensates in a magnetic waveguide
Gaseous Bose-Einstein condensates of 2-3 million atoms were loaded into a
microfabricated magnetic trap using optical tweezers. Subsequently, the
condensates were released into a magnetic waveguide and propagated 12 mm.
Single-mode propagation was observed along homogeneous segments of the
waveguide. Inhomogeneities in the guiding potential arose from geometric
deformations of the microfabricated wires and caused strong transverse
excitations. Such deformations may restrict the waveguide physics that can be
explored with propagating condensates.Comment: 5 pages, 4 figure
Realization of the quantum Toffoli gate with trapped ions
Algorithms for quantum information processing are usually decomposed into
sequences of quantum gate operations, most often realized with single- and two-
qubit gates[1]. While such operations constitute a universal set for quantum
computation, gates acting on more than two qubits can simplify the
implementation of complex quantum algorithms[2]. Thus, a single three-qubit
operation can replace a complex sequence of two-qubit gates, which in turn
promises faster execution with potentially higher Fidelity. One important
three-qubit operation is the quantum Toffoli gate which performs a NOT
operation on a target qubit depending on the state of two control qubits. Here
we present the first experimental realization of the quantum Toffoli gate in an
ion trap quantum computer. Our implementation is particular effcient as we
directly encode the relevant logic information in the motion of the ion string.
[1] DiVincenzo, D. P. Two-bit gates are universal for quantum computation.
cond-mat/9407022, Phys.Rev. A 51, 1015-1022 (1995). [2] Chiaverini, J. et al.
Realization of quantum error correction. Nature 432, 602-605 (2004).Comment: 11 pages, 2 figure
Trapped Rydberg Ions: From Spin Chains to Fast Quantum Gates
We study the dynamics of Rydberg ions trapped in a linear Paul trap, and
discuss the properties of ionic Rydberg states in the presence of the static
and time-dependent electric fields constituting the trap. The interactions in a
system of many ions are investigated and coupled equations of the internal
electronic states and the external oscillator modes of a linear ion chain are
derived. We show that strong dipole-dipole interactions among the ions can be
achieved by microwave dressing fields. Using low-angular momentum states with
large quantum defect the internal dynamics can be mapped onto an effective spin
model of a pair of dressed Rydberg states that describes the dynamics of
Rydberg excitations in the ion crystal. We demonstrate that excitation transfer
through the ion chain can be achieved on a nanosecond timescale and discuss the
implementation of a fast two-qubit gate in the ion chain.Comment: 26 pages, 9 figure
Dimensional and Temperature Crossover in Trapped Bose Gases
We investigate the long-range phase coherence of homogeneous and trapped Bose
gases as a function of the geometry of the trap, the temperature, and the
mean-field interactions in the weakly interacting limit. We explicitly take
into account the (quasi)condensate depletion due to quantum and thermal
fluctuations, i.e., we include the effects of both phase and density
fluctuations. In particular, we determine the phase diagram of the gas by
calculating the off-diagonal one-particle density matrix and discuss the
various crossovers that occur in this phase diagram and the feasibility of
their experimental observation in trapped Bose gases.Comment: One figure added, typos corrected, refernces adde
Radio-frequency dressed state potentials for neutral atoms
Potentials for atoms can be created by external fields acting on properties
like magnetic moment, charge, polarizability, or by oscillating fields which
couple internal states. The most prominent realization of the latter is the
optical dipole potential formed by coupling ground and electronically excited
states of an atom with light. Here we present an experimental investigation of
the remarkable properties of potentials derived from radio-frequency (RF)
coupling between electronic ground states. The coupling is magnetic and the
vector character allows to design state dependent potential landscapes. On atom
chips this enables robust coherent atom manipulation on much smaller spatial
scales than possible with static fields alone. We find no additional heating or
collisional loss up to densities approaching atoms / cm compared
to static magnetic traps. We demonstrate the creation of Bose-Einstein
condensates in RF potentials and investigate the difference in the interference
between two independently created and two coherently split condensates in
identical traps. All together this makes RF dressing a powerful new tool for
micro manipulation of atomic and molecular systems
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