12,788 research outputs found
Looking into DNA breathing dynamics via quantum physics
We study generic aspects of bubble dynamics in DNA under time dependent
perturbations, for example temperature change, by mapping the associated
Fokker-Planck equation to a quantum time-dependent Schroedinger equation with
imaginary time. In the static case we show that the eigenequation is exactly
the same as that of the -deformed nuclear liquid drop model, without the
issue of non-integer angular momentum. A universal breathing dynamics is
demonstrated by using an approximate method in quantum mechanics. The
calculated bubble autocorrelation function qualitatively agrees with
experimental data. Under time dependent modulations, utilizing the adiabatic
approximation, bubble properties reveal memory effects.Comment: 5 pages, 1 figur
Enhanced stability of hydrogen atoms at the graphene/graphane interface of nanoribbons
The thermal stability of graphene/graphane nanoribbons (GGNRs) is
investigated using density functional theory. It is found that the energy
barriers for the diffusion of hydrogen atoms on the zigzag and armchair
interfaces of GGNRs are 2.86 and 3.17 eV, respectively, while the diffusion
barrier of an isolated H atom on pristine graphene was only ~0.3 eV. These
results unambiguously demonstrate that the thermal stability of GGNRs can be
enhanced significantly by increasing the hydrogen diffusion barriers through
graphene/graphane interface engineering. This may provide new insights for
viable applications of GGNRs.Comment: 13 pages, 1 figure, 2 tables to appear in Appl. Phys. Let
Invalidity of Classes of Approximated Hall Effect Calculations
In this comment, I point out a number of approximated derivations for the
effective equation of motion, now been applied to d-wave superconductors by
Kopnin and Volovik are invalid. The major error in those approximated
derivations is the inappropriate use of the relaxation time approximation in
force-force correlation functions, or in force balance equations, or in similar
variations. This approximation is wrong and unnecessary.Comment: final version, minor changes, to appear in Phys. Rev. Let
Perfect Function Transfer in two- and three- dimensions without initialization
We find analytic models that can perfectly transfer, without state
initializati$ or remote collaboration, arbitrary functions in two- and
three-dimensional interacting bosonic and fermionic networks. We elaborate on a
possible implementation of state transfer through bosonic or fermionic atoms
trapped in optical lattices. A significant finding is that the state of a spin
qubit can be perfectly transferred through a fermionic system. Families of
Hamiltonians, both linear and nonlinear, are described which are related to the
linear Boson model and that enable the perfect transfer of arbitrary functions.
This includes entangled states such as decoherence-free subsystems enabling
noise protection of the transferred state.Comment: 4 pages, no figur
Tunneling of a Quantized Vortex: Roles of Pinning and Dissipation
We have performed a theoretical study of the effects of pinning potential and
dissipation on vortex tunneling in superconductors. Analytical results are
obtained in various limits relevant to experiment. In general we have found
that pinning and dissipation tend to suppress the effect of the vortex velocity
dependent part of the Magnus force on vortex tunneling.Comment: Latex, 12 page
Quantum heat transfer: A Born Oppenheimer method
We develop a Born-Oppenheimer type formalism for the description of quantum
thermal transport along hybrid nanoscale objects. Our formalism is suitable for
treating heat transfer in the off-resonant regime, where e.g., the relevant
vibrational modes of the interlocated molecule are high relative to typical
bath frequencies, and at low temperatures when tunneling effects dominate. A
general expression for the thermal energy current is accomplished, in the form
of a generalized Landauer formula. In the harmonic limit this expression
reduces to the standard Landauer result for heat transfer, while in the
presence of nonlinearities multiphonon tunneling effects are realized
Casimir Invariants for Systems Undergoing Collective Motion
Dicke states are states of a collection of particles which have been under
active investigation for several reasons. One reason is that the decay rates of
these states can be quite different from a set of independently evolving
particles. Another reason is that a particular class of these states are
decoherence-free or noiseless with respect to a set of errors. These noiseless
states, or more generally subsystems, can avoid certain types of errors in
quantum information processing devices. Here we provide a method for
calculating invariants of systems of particles undergoing collective motions.
These invariants can be used to determine a complete set of commuting
observables for a class of Dicke states as well as identify possible logical
operations for decoherence-free/noiseless subsystems. Our method is quite
general and provides results for cases where the constituent particles have
more than two internal states.Comment: 5 page
One-spin quantum logic gates from exchange interactions and a global magnetic field
It has been widely assumed that one-qubit gates in spin-based quantum
computers suffer from severe technical difficulties. We show that one-qubit
gates can in fact be generated using only modest and presently feasible
technological requirements. Our solution uses only global magnetic fields and
controllable Heisenberg exchange interactions, thus circumventing the need for
single-spin addressing.Comment: 4 pages, incl. 1 figure. This significantly modified version accepted
for publication in Phys. Rev. Let
Dissipative Tunneling in 2 DEG: Effect of Magnetic Field, Impurity and Temperature
We have studied the transport process in the two dimensional electron gas
(2DEG) in presence of a magnetic field and a dissipative environment at
temperature T. By means of imaginary time series functional integral method we
calculate the decay rates at finite temperature and in the presence of
dissipation. We have studied decay rates for wide range of temperatures -- from
the thermally activated region to very low temperature region where the system
decays by quantum tunneling. We have shown that dissipation and impurity helps
the tunneling. We have also shown that tunneling is strongly affected by the
magnetic field. We have demonstrated analytical results for all the cases
mentioned above.Comment: 8 pages, 2 figure
Rubidium "whiskers" in a vapor cell
Crystals of metallic rubidium are observed ``growing'' from paraffin coating
of buffer-gas-free glass vapor cells. The crystals have uniform square
cross-section, m on the side, and reach several mm in length.Comment: 2 pages, 1 figur
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