360 research outputs found
Creation and dynamics of two-dimensional skyrmions in antiferromagnetic spin-1 Bose-Einstein condensates
We numerically simulate the creation process of two-dimensional skyrmionic
excitations in antiferromagnetic spin-1 Bose--Einstein condensates by solving
the full three-dimensional dynamics of the system from the Gross--Pitaevskii
equation. Our simulations reproduce quantitatively the experimental results of
[Choi et al., Phys. Rev. Lett. 108, 035301 (2012)] without any fitting
parameters. Furthermore, we examine the stability of the skyrmion by computing
the temporal evolution of the condensate in a harmonic potential. The presence
of both the quadratic Zeeman effect and dissipation in the simulations is vital
for reproducing the experimentally observed decay time.Comment: 6 pages, 7 figure
Quantum knots in Bose-Einstein condensates created by counterdiabatic control
We theoretically study the creation of knot structures in the polar phase of
spin-1 BECs using the counterdiabatic protocol in an unusual fashion. We
provide an analytic solution to the evolution of the external magnetic field
that is used to imprint the knots. As confirmed by our simulations using the
full three-dimensional spin-1 Gross-Pitaevskii equation, our method allows for
the precise control of the Hopf charge as well as the creation time of the
knots. The knots with Hopf charge exceeding unity display multiple nested Hopf
links.Comment: 7 pages, 6 figure
Adiabatically steered open quantum systems: Master equation and optimal phase
We introduce an alternative way to derive the generalized form of the master
equation recently presented by J. P. Pekola et al. [Phys. Rev. Lett. 105,
030401 (2010)] for an adiabatically steered two-level quantum system
interacting with a Markovian environment. The original derivation employed the
effective Hamiltonian in the adiabatic basis with the standard interaction
picture approach but without the usual secular approximation. Our approach is
based on utilizing a master equation for a non-steered system in the first
super-adiabatic basis. It is potentially efficient in obtaining higher-order
equations. Furthermore, we show how to select the phases of the adiabatic
eigenstates to minimize the local adiabatic parameter and how this selection
leads to states which are invariant under a local gauge change. We also discuss
the effects of the adiabatic noncyclic geometric phase on the master equation.Comment: 8 pages, no figures, final versio
Non-Abelian geometric phases in ground state Josephson devices
We present a superconducting circuit in which non-Abelian geometric
transformations can be realized using an adiabatic parameter cycle. In contrast
to previous proposals, we employ quantum evolution in the ground state. We
propose an experiment in which the transition from non-Abelian to Abelian
cycles can be observed by measuring the pumped charge as a function of the
period of the cycle. Alternatively, the non-Abelian phase can be detected using
a single-electron transistor working as a charge sensor.Comment: 5 pages, 3 figures; added references and clarified discussion about
earlier research on the fiel
Dynamically stable multiply quantized vortices in dilute Bose-Einstein condensates
Multiquantum vortices in dilute atomic Bose-Einstein condensates confined in
long cigar-shaped traps are known to be both energetically and dynamically
unstable. They tend to split into single-quantum vortices even in the ultralow
temperature limit with vanishingly weak dissipation, which has also been
confirmed in the recent experiments [Y. Shin et al., Phys. Rev. Lett. 93,
160406 (2004)] utilizing the so-called topological phase engineering method to
create multiquantum vortices. We study the stability properties of multiquantum
vortices in different trap geometries by solving the Bogoliubov excitation
spectra for such states. We find that there are regions in the trap asymmetry
and condensate interaction strength plane in which the splitting instability of
multiquantum vortices is suppressed, and hence they are dynamically stable. For
example, the doubly quantized vortex can be made dynamically stable even in
spherical traps within a wide range of interaction strength values. We expect
that this suppression of vortex-splitting instability can be experimentally
verified.Comment: 5 pages, 6 figure
Quantum Treatment for Bose-Einstein Condensation in Non-Equilibrium Systems
We develop an approach based on stochastic quantum trajectories for an
incoherently pumped system of interacting bosons relaxing their energy in a
thermal reservoir. Our approach enables the study of the versatile coherence
properties of the system. We apply the model to exciton polaritons in a
semiconductor microcavity. Our results demonstrate the onset of macroscopic
occupation in the lowest-energy mode accompanied by the establishment of both
temporal and spatial coherence. We show that temporal coherence exhibits a
transition from a thermal to coherent statistics and the spatial coherence
reveals off-diagonal long-range order.Comment: 5 Pages, 3 figure
Ground-state geometric quantum computing in superconducting systems
We present a theoretical proposal for the implementation of geometric quantum
computing based on a Hamiltonian which has a doubly degenerate ground state.
Thus the system which is steered adiabatically, remains in the ground-state.
The proposed physical implementation relies on a superconducting circuit
composed of three SQUIDs and two superconducting islands with the charge states
encoding the logical states. We obtain a universal set of single-qubit gates
and implement a non-trivial two-qubit gate exploiting the mutual inductance
between two neighboring circuits, allowing us to realize a fully geometric
ground-state quantum computing. The introduced paradigm for the implementation
of geometric quantum computing is expected to be robust against environmental
effects.Comment: 9 pages, 5 figures. Final version with notation and typos correcte
Geometric quantum gates with superconducting qubits
We suggest a scheme to implement a universal set of non-Abelian geometric
transformations for a single logical qubit composed of three superconducting
transmon qubits coupled to a single cavity. The scheme utilizes an adiabatic
evolution in a rotating frame induced by the effective tripod Hamiltonian which
is achieved by longitudinal driving of the transmons. The proposal is
experimentally feasible with the current state of the art and could serve as a
first proof of principle for geometric quantum computing.Comment: 7 pages, 5 figure
- âŠ