96 research outputs found
Optimizing the catching of atoms or molecules in two-dimensional traps
Single-photon cooling is a recently introduced method to cool atoms and
molecules for which standard methods might not be applicable. We numerically
examine this method in a two-dimensional wedge trap as well as in a
two-dimensional harmonic trap. An element of the method is an optical dipole
box trapping atoms irreversibly. We show that the cooling efficiency of the
single-photon method can be improved by optimizing the trajectory of this
optical dipole box.Comment: 8 pages, 11 figures, improved version with corrected typos et
Determining realistic electrochemical stability windows of electrolytes for electrical double layer capacitors
Electrical double-layer capacitors are a key building block for energy storage applications, including renewable energies, wherever high power is needed. Most research on electrolytes in this field focuses on improving their electrochemical stability. This improves the energy density as it scales with the square of the maximum operative voltage. However, the decisive criteria to assess the electrochemical stability window of electrolytes are unclear. Consequently, new electrolyte candidates are often presented with unrealistic high stability windows and their performance is difficult to compare. In this Minireview, an overview of electrochemical stability window determination methods is presented. It is argued that constant voltage lifetime tests are needed to confirm the electrochemical stability window determined by any other method. Also, the importance of using realistic working electrodes, reference electrodes, and cycling protocols are highlighted. Finally, an industrial perspective on what is necessary to yield results relevant to applications is given
Fast atomic transport without vibrational heating
We use the dynamical invariants associated with the Hamiltonian of an atom in
a one dimensional moving trap to inverse engineer the trap motion and perform
fast atomic transport without final vibrational heating. The atom is driven
non-adiabatically through a shortcut to the result of adiabatic, slow trap
motion. For harmonic potentials this only requires designing appropriate trap
trajectories, whereas perfect transport in anharmonic traps may be achieved by
applying an extra field to compensate the forces in the rest frame of the trap.
The results can be extended to atom stopping or launching. The limitations due
to geometrical constraints, energies and accelerations involved are analyzed,
as well as the relation to previous approaches (based on classical trajectories
or "fast-forward" and "bang-bang" methods) which can be integrated in the
invariant-based framework.Comment: 10 pages, 5 figure
Asymmetric Wave Propagation Through Nonlinear PT-symmetric Oligomers
In the present paper, we consider nonlinear PT-symmetric dimers and trimers
(more generally, oligomers) embedded within a linear Schr{\"o}dinger lattice.
We examine the stationary states of such chains in the form of plane waves, and
analytically compute their reflection and transmission coefficients through the
nonlinear PT symmetric oligomer, as well as the corresponding rectification
factors which clearly illustrate the asymmetry between left and right
propagation in such systems. We examine not only the existence but also the
dynamical stability of the plane wave states and interestingly find them to be
generically unstable. Lastly, we generalize our numerical considerations to the
more physically relevant case of Gaussian initial wavepackets and confirm that
the asymmetry in the transmission properties persists in the case of such
wavepackets, as well
Self-dual Spectral Singularities and Coherent Perfect Absorbing Lasers without PT-symmetry
A PT-symmetric optically active medium that lases at the threshold gain also
acts as a complete perfect absorber at the laser wavelength. This is because
spectral singularities of PT-symmetric complex potentials are always
accompanied by their time-reversal dual. We investigate the significance of
PT-symmetry for the appearance of these self-dual spectral singularities. In
particular, using a realistic optical system we show that self-dual spectral
singularities can emerge also for non-PT-symmetric configurations. This
signifies the existence of non-PT-symmetric CPA-lasers.Comment: 11 pages, 3 figures, 1 table, accepted for publication in J. Phys.
Improvement by laser quenching of an "atom diode": a one-way barrier for ultra-cold atoms
Different laser devices working as ``atom diodes'' or ``one-way barriers''
for ultra-cold atoms have been proposed recently. They transmit ground state
level atoms coming from one side, say from the left, but reflect them when they
come from the other side. We combine a previous model, consisting of the
stimulated Raman adiabatic passage (STIRAP) from the ground to an excited state
and a state-selective mirror potential, with a localized quenching laser which
produces spontaneous decay back to the ground state. This avoids backwards
motion, provides more control of the decay process and therefore a more compact
and useful device.Comment: 6 page
Quantum optical time-of-arrival model in three dimensions
We investigate the three-dimensional formulation of a recently proposed
operational arrival-time model. It is shown that within typical conditions for
optical transitions the results of the simple one-dimensional version are
generally valid. Differences that may occur are consequences of Doppler and
momentum-transfer effects. Ways to minimize these are discussed.Comment: 14 pages, 5 figure
Tunneling times with covariant measurements
We consider the time delay of massive, non-relativistic, one-dimensional
particles due to a tunneling potential. In this setting the well-known Hartman
effect asserts that often the sub-ensemble of particles going through the
tunnel seems to cross the tunnel region instantaneously. An obstacle to the
utilization of this effect for getting faster signals is the exponential
damping by the tunnel, so there seems to be a trade-off between speedup and
intensity. In this paper we prove that this trade-off is never in favor of
faster signals: the probability for a signal to reach its destination before
some deadline is always reduced by the tunnel, for arbitrary incoming states,
arbitrary positive and compactly supported tunnel potentials, and arbitrary
detectors. More specifically, we show this for several different ways to define
``the same incoming state'' and ''the same detector'' when comparing the
settings with and without tunnel potential. The arrival time measurements are
expressed in the time-covariant approach, but we also allow the detection to be
a localization measurement at a later time.Comment: 12 pages, 2 figure
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