11,330 research outputs found
Quantum chaos with spin-chains in pulsed magnetic fields
Recently it was found that the dynamics in a Heisenberg spin-chain subjected
to a sequence of periodic pulses from an external, parabolic, magnetic field
can have a close correspondence with the quantum kicked rotor (QKR). The QKR is
a key paradigm of quantum chaos; it has as its classical limit the well-known
Standard Map. It was found that a single spin excitation could be converted
into a pair of non-dispersive, counter-propagating spin coherent states
equivalent to the accelerator modes of the Standard Map. Here we consider how
other types of quantum chaotic systems such as a double-kicked quantum rotor or
a quantum rotor with a double-well potential might be realized with spin
chains; we discuss the possibilities regarding manipulation of the one-magnon
spin waves.Comment: 10 pages, 4 figures. Submitted to PTP special issue for QMC200
The Quantum Algebraic Structure of the Twisted XXZ Chain
We consider the Quantum Inverse Scattering Method with a new R-matrix
depending on two parameters and . We find that the underlying algebraic
structure is the two-parameter deformed algebra enlarged by
introducing an element belonging to the centre. The corresponding Hamiltonian
describes the spin-1/2 XXZ model with twisted periodic boundary conditions.Comment: LateX file, 9 pages, Minor changes (including authors` names in the
hep-th heading
Periodically-driven cold atoms: the role of the phase
Numerous theoretical and experimental studies have investigated the dynamics
of cold atoms subjected to time periodic fields. Novel effects dependent on the
amplitude and frequency of the driving field, such as Coherent Destruction of
Tunneling have been identified and observed. However, in the last year or so,
three distinct types of experiments have demonstrated for the first time,
interesting behaviour associated with the driving phase: i.e. for systems
experiencing a driving field of general form ,
different types of large scale oscillations and directed motion were observed.
We investigate and explain the phenomenon of Super-Bloch Oscillations (SBOs) in
relation to the other experiments and address the role of initial phase in
general. We analyse and compare the role of in systems with homogeneous
forces (), such as cold atoms in shaken or amplitude-modulated
optical lattices, as well as non-homogeneous forces (), such
as the sloshing of atoms in driven traps, and clarify the physical origin of
the different -dependent effects.Comment: 10 pages, 1 figur
Probing tiny convective cores with the acoustic modes of lowest degree
Solar-like oscillations are expected to be excited in stars of up to about
1.6 solar masses. Most of these stars will have convective cores during their
Main-sequence evolution. At the edges of these convective cores there is a
rapid variation in the sound speed which influences the frequencies of acoustic
oscillations. In this paper we build on earlier work by Cunha and Metcalfe, to
investigate further the impact that these rapid structural variations have on
different p-mode frequency combinations, involving modes of low degree. In
particular, we adopt a different expression to describe the sound speed
variation at the edge of the core, which we show to reproduce more closely the
profiles derived from the equilibrium models. We analyse the impact of this
change on the frequency perturbation derived for radial modes. Moreover, we
consider three different small frequency separations involving, respectively,
modes of degree l = 0, 1, 2, 3; l = 0, 1; and l = 0, 2, and show that they are
all significantly affected by the sharp sound speed variation at the edge of
the core. In particular, we confirm that the frequency derivative of the
diagnostic tool that combines modes of degree up to 3 can potentially be used
to infer directly the amplitude of the relative sound speed variation at the
edge of the core. Concerning the other two diagnostic tools, we show that at
high frequencies they can be up to a few microhertzs smaller than what would be
expected in the absence of the rapid structural variation at the edge of the
core. Also, we show that the absolute values of their frequency derivatives are
significantly increased, in a manner that is strongly dependent on stellar age.Comment: 7 pages. submitted to A&
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
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