6,323 research outputs found
Magnetic field induced band insulator to Mott insulator transformations in 4-component alkali fermions at half-filling
Under the influence of an external magnetic field and spin-changing
collisions, the band insulator (BI) state of one-dimensional (1D) s-wave
repulsively interacting 4-component fermions at half-filling transforms into
Mott insulator (MI) states with spontaneously broken translational symmetry: a
dimerized state for shallow lattices and a N{\'e}el state for deep lattices via
an intermediate topological state. Since a BI has vanishing entropy per
particle, these MI phases could be particularly inviting for experimental
realization under the similar conditions as those for K atoms [1],
provided the magnetic field is changed adiabatically.Comment: 5 eps figure
Renormings of
We investigate the best order of smoothness of . We prove in
particular that there exists a -smooth bump function on if
and only if and are both even integers and is a multiple of .Comment: 18 pages; AMS-Te
Scaling-up quantum heat engines efficiently via shortcuts to adiabaticity
The finite-time operation of a quantum heat engine that uses a single
particle as a working medium generally increases the output power at the
expense of inducing friction that lowers the cycle efficiency. We propose to
scale up a quantum heat engine utilizing a many-particle working medium in
combination with the use of shortcuts to adiabaticity to boost the nonadiabatic
performance by eliminating quantum friction and reducing the cycle time. To
this end, we first analyze the finite-time thermodynamics of a quantum Otto
cycle implemented with a quantum fluid confined in a time-dependent harmonic
trap. We show that nonadiabatic effects can be controlled and tailored to match
the adiabatic performance using a variety of shortcuts to adiabaticity. As a
result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat
engine exhibits no friction and the cycle can be run at maximum efficiency with
a tunable output power. We demonstrate our results with a working medium
consisting of particles with inverse-square pairwise interactions, that
includes noninteracting and hard-core bosons as limiting cases.Comment: 15 pages, 3 figures; typo in Eq. (51) fixed. Feature paper in the
Special Issue "Quantum Thermodynamics" edited by Prof. Dr. Ronnie Koslof
Working with OpenCL to Speed Up a Genetic Programming Financial Forecasting Algorithm: Initial Results
The genetic programming tool EDDIE has been shown to be a successful financial forecasting tool, however it has suffered from an increase in execution time as new features have been added. Speed is an important aspect in financial problems, especially in the field of algorithmic trading, where a delay in taking a decision could cost millions. To offset this performance loss, EDDIE has been modified to take advantage of multi-core CPUs and dedicated GPUs. This has been achieved by modifying the candidate solution evaluation to use an OpenCL kernel, allowing the parallel evaluation of solutions. Our computational results have shown improvements in the running time of EDDIE when the evaluation was delegated to the OpenCL kernel running on a multi-core CPU, with speed ups up to 21 times faster than the original EDDIE algorithm. While most previous works in the literature reported significantly improvements in performance when running an OpenCL kernel on a GPU device, we did not observe this in our results. Further investigation revealed that memory copying overheads and branching code in the kernel are potentially causes of the (under-)performance of the OpenCL kernel when running on the GPU device
An effective quantum mechanism for mass generation in diffeomorphism-invariant theories
We propose a scenario for particle-mass generation, assuming the existence of
a physical regime where, firstly, physical particles can be considered as
point-like objects moving in a background space-time and, secondly, their mere
presence spoils the invariance under the local diffeomorphism group, resulting
in an anomalous realization of the latter. Under these hypotheses, we describe
mass generation starting from the massless free theory. The mechanism is not
sensitive to the detailed description of the underlying theory at higher
energies, leaning only on general structural features of it, specifically
diffeomorphism invariance.Comment: 8 pages, LaTeX, no figures; version accepted for publication in MPL
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