4,254 research outputs found
Shortcuts to adiabaticity for an ion in a rotating radially-tight trap
We engineer the fast rotation of a quantum particle confined in an
effectively one-dimensional, harmonic trap, for a predetermined rotation angle
and time, avoiding final excitation. Different schemes are proposed with
different speed limits that depend on the control capabilities. We also make
use of trap rotations to create squeezed states without manipulating the trap
frequencies.Comment: 11 pages, 6 figure
Optimal trajectories for efficient atomic transport without final excitation
We design optimal harmonic-trap trajectories to transport cold atoms without
final excitation, combining an inverse engineering techniqe based on
Lewis-Riesenfeld invariants with optimal control theory. Since actual traps are
not really harmonic, we keep the relative displacement between the center of
mass and the trap center bounded. Under this constraint, optimal protocols are
found according to different physical criteria. The minimum time solution has a
"bang-bang" form, and the minimum displacement solution is of "bang-off-bang"
form. The optimal trajectories for minimizing the transient energy are also
discussed.Comment: 10 pages, 7 figure
Emergence of superfluid transport in a dynamical system of ultracold atoms
The dynamics of a Bose-Einstein condensate is studied theoretically in a
combined periodic plus harmonic external potential. Different dynamical regimes
of stable and unstable collective dipole and Bloch oscillations are analysed in
terms of a quantum mechanical pendulum model. Nonlinear interactions are shown
to counteract quantum-mechanical dephasing and lead to phase-coherent,
superfluid transport
Approaching the adiabatic timescale with machine-learning
The control and manipulation of quantum systems without excitation is
challenging, due to the complexities in fully modeling such systems accurately
and the difficulties in controlling these inherently fragile systems
experimentally. For example, while protocols to decompress Bose-Einstein
condensates (BEC) faster than the adiabatic timescale (without excitation or
loss) have been well developed theoretically, experimental implementations of
these protocols have yet to reach speeds faster than the adiabatic timescale.
In this work, we experimentally demonstrate an alternative approach based on a
machine learning algorithm which makes progress towards this goal. The
algorithm is given control of the coupled decompression and transport of a
metastable helium condensate, with its performance determined after each
experimental iteration by measuring the excitations of the resultant BEC. After
each iteration the algorithm adjusts its internal model of the system to create
an improved control output for the next iteration. Given sufficient control
over the decompression, the algorithm converges to a novel solution that sets
the current speed record in relation to the adiabatic timescale, beating out
other experimental realizations based on theoretical approaches. This method
presents a feasible approach for implementing fast state preparations or
transformations in other quantum systems, without requiring a solution to a
theoretical model of the system. Implications for fundamental physics and
cooling are discussed.Comment: 7 pages main text, 2 pages supporting informatio
Generalized HydroDynamics on an Atom Chip
The emergence of a special type of fluid-like behavior at large scales in
one-dimensional (1d) quantum integrable systems, theoretically predicted in
2016, is established experimentally, by monitoring the time evolution of the in
situ density profile of a single 1d cloud of atoms trapped on
an atom chip after a quench of the longitudinal trapping potential. The theory
can be viewed as a dynamical extension of the thermodynamics of Yang and Yang,
and applies to the whole range of repulsion strength and temperature of the
gas. The measurements, performed on weakly interacting atomic clouds that lie
at the crossover between the quasicondensate and the ideal Bose gas regimes,
are in very good agreement with the 2016 theory. This contrasts with the
previously existing 'conventional' hydrodynamic approach---that relies on the
assumption of local thermal equilibrium---, which is unable to reproduce the
experimental data.Comment: v1: 6+11 pages, 4+4 figures. v2: published version, 6+11 pages, 4+6
figure
Experimental observation of moving intrinsic localized modes in germanium
Deep level transient spectroscopy shows that defects created by alpha
irradiation of germanium are annealed by low energy plasma ions up to a depth
of several thousand lattice units. The plasma ions have energies of 2-8eV and
therefore can deliver energies of the order of a few eV to the germanium atoms.
The most abundant defect is identified as the E-center, a complex of the dopant
antimony and a vacancy with and annealing energy of 1.3eV as determined by our
measurements. The inductively coupled plasma has a very low density and a very
low flux of ions. This implies that the ion impacts are almost isolated both in
time and at the surface of the semiconductor. We conclude that energy of the
order of an eV is able to travel a large distance in germanium in a localized
way and is delivered to the defects effectively. The most likely candidates are
vibrational nonlinear wave packets known as intrinsic localized modes, which
exist for a limited range of energies. This property is coherent with the fact
that more energetic ions are less efficient at producing the annealing effect.Comment: 20 pages, 10 figure
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