12,989 research outputs found
Quantum vortex dynamics in two-dimensional neutral superfluids
We derive an effective action for the vortex position degree-of-freedom in a
superfluid by integrating out condensate phase and density fluctuation
environmental modes. When the quantum dynamics of environmental fluctuations is
neglected, we confirm the occurrence of the vortex Magnus force and obtain an
expression for the vortex mass. We find that this adiabatic approximation is
valid only when the superfluid droplet radius , or the typical distance
between vortices, is very much larger than the coherence length . We go
beyond the adiabatic approximation numerically, accounting for the quantum
dynamics of environmental modes and capturing their dissipative coupling to
condensate dynamics. For the case of an optical-lattice superfluid we
demonstrate that vortex motion damping can be adjusted by tuning the ratio
between the tunneling energy and the on-site interaction energy . We
comment on the possibility of realizing vortex Landau level physics.Comment: 14 pages, 10 figures, accepted by PRA with corrected references and
typo
Gravity in a Box
We consider a brane-world construction which incorporates a finite region of
flat space, ``the box,'' surrounded by a region of anti-de Sitter space. This
hybrid construction provides a framework which interpolates between the
scenario proposed by Arkani-Hamed, Dimopoulos and Dvali, and that proposed by
Randall and Sundrum. Within this composite framework, we investigate the
effects of resonant modes on four-dimensional gravity. We also show that, on a
probe brane in the anti-de Sitter region, there is enhanced production of
on-shell nonresonant modes. We compare our model to some recent attempts to
incorporate the Randall-Sundrum scenario into superstring theory.Comment: 15 pages, 1 figur
Local Electronic Structure around a Single Impurity in an Anderson Lattice Model for Topological Kondo Insulators
Shortly after the discovery of topological band insulators, the topological
Kondo insulators (TKIs) have also been theoretically predicted. The latter has
ignited revival interest in the properties of Kondo insulators. Currently, the
feasibility of topological nature in SmB has been intensively analyzed by
several complementary probes. Here by starting with a minimal-orbital Anderson
lattice model, we explore the local electronic structure in a Kondo insulator.
We show that the two strong topological regimes sandwiching the weak
topological regime give rise to a single Dirac cone, which is located near the
center or corner of the surface Brillouin zone. We further find that, when a
single impurity is placed on the surface, low-energy resonance states are
induced in the weak scattering limit for the strong TKI regimes and the
resonance level moves monotonically across the hybridization gap with the
strength of impurity scattering potential; while low energy states can only be
induced in the unitary scattering limit for the weak TKI regime, where the
resonance level moves universally toward the center of the hybridization gap.
These impurity induced low-energy quasiparticles will lead to characteristic
signatures in scanning tunneling microscopy/spectroscopy, which has recently
found success in probing into exotic properties in heavy fermion systems.Comment: 8 pages with 4 eps figures embedded, references update
Variational quantum regression algorithm with encoded data structure
Variational quantum algorithms (VQAs) prevail to solve practical problems
such as combinatorial optimization, quantum chemistry simulation, quantum
machine learning, and quantum error correction on noisy quantum computers. For
variational quantum machine learning, a variational algorithm with model
interpretability built into the algorithm is yet to be exploited. In this
paper, we construct a quantum regression algorithm and identify the direct
relation of variational parameters to learned regression coefficients, while
employing a circuit that directly encodes the data in quantum amplitudes
reflecting the structure of the classical data table. The algorithm is
particularly suitable for well-connected qubits. With compressed encoding and
digital-analog gate operation, the run time complexity is logarithmically more
advantageous than that for digital 2-local gate native hardware with the number
of data entries encoded, a decent improvement in noisy intermediate-scale
quantum computers and a minor improvement for large-scale quantum computing Our
suggested method of compressed binary encoding offers a remarkable reduction in
the number of physical qubits needed when compared to the traditional
one-hot-encoding technique with the same input data. The algorithm inherently
performs linear regression but can also be used easily for nonlinear regression
by building nonlinear features into the training data. In terms of measured
cost function which distinguishes a good model from a poor one for model
training, it will be effective only when the number of features is much less
than the number of records for the encoded data structure to be observable. To
echo this finding and mitigate hardware noise in practice, the ensemble model
training from the quantum regression model learning with important feature
selection from regularization is incorporated and illustrated numerically
Phonon mediated quantum spin simulator employing a planar ionic crystal in a Penning trap
We derive the normal modes for a rotating Coulomb ion crystal in a Penning
trap, quantize the motional degrees of freedom, and illustrate how they can by
driven by a spin-dependent optical dipole force to create a quantum spin
simulator on a triangular lattice with hundreds of spins. The analysis for the
axial modes (oscillations perpendicular to the two-dimensional crystal plane)
follow a standard normal-mode analysis, while the remaining planar modes are
more complicated to analyze because they have velocity-dependent forces in the
rotating frame. After quantizing the normal modes into phonons, we illustrate
some of the different spin-spin interactions that can be generated by
entangling the motional degrees of freedom with the spin degrees of freedom via
a spin-dependent optical dipole force. In addition to the well-known power-law
dependence of the spin-spin interactions when driving the axial modes blue of
phonon band, we notice certain parameter regimes in which the level of
frustration between the spins can be engineered by driving the axial or planar
phonon modes at different energies. These systems may allow for the analog
simulation of quantum spin glasses with large numbers of spins.Comment: 20 pages, 17 figure
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