1,032 research outputs found
Zeno and anti-Zeno effects for quantum Brownian motion
In this paper we investigate the occurrence of the Zeno and anti-Zeno effects
for quantum Brownian motion. We single out the parameters of both the system
and the reservoir governing the crossover between Zeno and anti-Zeno dynamics.
We demonstrate that, for high reservoir temperatures, the short time behaviour
of environment induced decoherence is the ultimate responsible for the
occurrence of either the Zeno or the anti-Zeno effect. Finally we suggest a way
to manipulate the decay rate of the system and to observe a controlled
continuous passage from decay suppression to decay acceleration using
engineered reservoirs in the trapped ion context .Comment: 4 pages, 1 figure. v2: Replaced with the published version. Minor
modifications in the text and titl
Cold collisions between atoms in optical lattices
We have simulated binary collisions between atoms in optical lattices during
Sisyphus cooling. Our Monte Carlo Wave Function simulations show that the
collisions selectively accelerate mainly the hotter atoms in the thermal
ensemble, and thus affect the steady state which one would normally expect to
reach in Sisyphus cooling without collisions.Comment: 4 pages, 1 figur
Efficient Two-dimensional Subrecoil Raman Cooling of Atoms in a Tripod Configuration
We present an efficient method for subrecoil cooling of neutral atoms by
applying Raman cooling in 2D to a four-level tripod-system. The atoms can be
cooled simultaneously in two directions using only three laser beams. We
describe the cooling process with a simple model showing that the momentum
distribution can be rapidly narrowed to velocity spread down to
, corresponding to effective temperature equal to
. This method opens new possibilities for cooling of neutral
atoms.Comment: 6 pages, 3 figure
Non-Markovian waiting time distribution
Simulation methods based on stochastic realizations of state vector
evolutions are commonly used tools to solve open quantum system dynamics, both
in the Markovian and non-Markovian regime. Here, we address the question of
waiting time distribution (WTD) of quantum jumps for non-Markovian systems. We
generalize Markovian quantum trajectory methods in the sense of deriving an
exact analytical WTD for non-Markovian quantum dynamics and show explicitly how
to construct this distribution for certain commonly used quantum optical
systems.Comment: journal versio
Temporal Interferometry: A Mechanism for Controlling Qubit Transitions During Twisted Rapid Passage with Possible Application to Quantum Computing
In an adiabatic rapid passage experiment, the Bloch vector of a two-level
system (qubit) is inverted by slowly inverting an external field to which it is
coupled, and along which it is initially aligned. In twisted rapid passage, the
external field is allowed to twist around its initial direction with azimuthal
angle at the same time that it is inverted. For polynomial twist:
. We show that for , multiple avoided crossings
can occur during the inversion of the external field, and that these crossings
give rise to strong interference effects in the qubit transition probability.
The transition probability is found to be a function of the twist strength ,
which can be used to control the time-separation of the avoided crossings, and
hence the character of the interference. Constructive and destructive
interference are possible. The interference effects are a consequence of the
temporal phase coherence of the wavefunction. The ability to vary this
coherence by varying the temporal separation of the avoided crossings renders
twisted rapid passage with adjustable twist strength into a temporal
interferometer through which qubit transitions can be greatly enhanced or
suppressed. Possible application of this interference mechanism to construction
of fast fault-tolerant quantum CNOT and NOT gates is discussed.Comment: 29 pages, 16 figures, submitted to Phys. Rev.
Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields
We derive and apply an optical Bloch equation (OBE) model for describing
collisions of ground and excited laser cooled alkali atoms in the presence of
near-resonant light. Typically these collisions lead to loss of atoms from
traps. We compare the results obtained with a quantum mechanical complex
potential treatment, semiclassical Landau-Zener models with decay, and a
quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate
the OBE method in both adiabatic and diabatic representations. We calculate the
laser intensity dependence of collision probabilities and find that the
adiabatic OBE results agree quantitatively with those of the MCWP calculation,
and qualitatively with the semiclassical Landau-Zener model with delayed decay,
but that the complex potential method or the traditional Landau-Zener model
fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also
http://www.physics.helsinki.fi/~kasuomin
Population trapping due to cavity losses
In population trapping the occupation of a decaying quantum level keeps a
constant non-zero value. We show that an atom-cavity system interacting with an
environment characterized by a non-flat spectrum, in the non-Markovian limit,
exhibits such a behavior, effectively realizing the preservation of
nonclassical states against dissipation. Our results allow to understand the
role of cavity losses in hybrid solid state systems and pave the way to the
proper description of leakage in the recently developed cavity quantum
electrodynamic systems.Comment: 4 pages, 3 figures, version accepted for publication on Phys. Rev.
Estimating Operability of Ships in Ridged Ice Fields
A method for estimating ship's resistance caused by sea ice ridge keels is revised and used as a part of a method for predicting performance of ships in ridged ice conditions. The resistance method is based on a continuum plasticity model of ridge rubble and is simple to compute. The performance prediction method combines deterministic simulations of ship motion with probabilistic modelling of ridged ice fields. Performance estimates given by the model are distribution of attainable mean speeds for given ice conditions and probability of the ship being able to operate independently. A comprehensive sensitivity analysis was performed to gain insight into the model and identify possible problematic parameters. The sensitivity analysis covered both the ice conditions and modelling assumptions. Two data-sets were used to test the simulation method. One set included the depth profile of sea ice, machinery data and the speed of a ship operating in ridged ice. The resistance method was able to predict the meanspeed over 3km well. The second data-set consisted of a history of ship's speeds and positions from AIS data and ice conditions estimated by a numerical ice model HELMI, developed in the Finnish Meteorological Institute. Observed mean speeds were mostly well within the distributions of mean speeds simulated by the transit simulation model. Predictions of independent operation were also promising.Peer reviewe
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