7,136 research outputs found
High probability state transfer in spin-1/2 chains: Analytical and numerical approaches
This article is devoted to the development of analytical and numerical
approaches to the problem of the end-to-end quantum state transfer along the
spin-1/2 chain using two methods: (a) a homogeneous spin chain with week end
bonds and equal Larmor frequencies and (b) a homogeneous spin chain with end
Larmor frequencies different from inner ones. A tridiagonal matrix
representation of the XY Hamiltonian with nearest neighbor interactions
relevant to the quantum state transfer is exactly diagonalized for a
combination of the above two methods. In order to take into account
interactions of the remote spins we used numerical simulations of the quantum
state transfer in ten-node chains. We compare the state transfer times obtained
using the two above methods for chains governed by the both XY and XXZ
Hamiltonians and using both nearest neighbor and all node interactions.Comment: 16 pages, 5 figure
Magneto-optical Feshbach resonance: Controlling cold collision with quantum interference
We propose a method of controlling two-atom interaction using both magnetic
and laser fields. We analyse the role of quantum interference between magnetic
and optical Feshbach resonances in controlling cold collision. In particular,
we demonstrate that this method allows us to suppress inelastic and enhance
elastic scattering cross sections. Quantum interference is shown to modify
significantly the threshold behaviour and resonant interaction of ultracold
atoms. Furthermore, we show that it is possible to manipulate not only the
spherically symmetric s-wave interaction but also the anisotropic higher
partial-wave interactions which are particularly important for high temperature
superfluid or superconducting phases of matter.Comment: 7 pages 3 figures, some minor errors are corrected, Accepted in J.
Phys.
Multiple Quantum NMR Dynamics in Dipolar Ordered Spin Systems
We investigate analytically and numerically the Multiple Quantum (MQ) NMR
dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole
interactions in the case of the dipolar ordered initial state. We suggest two
different methods of MQ NMR. One of them is based on the measurement of the
dipolar temperature in the quasi-equilibrium state which establishes after the
time of order T2 after the MQ NMR experiment. The other method uses an
additional resonance 45^0 -pulse after the preparation period of the standard
MQ NMR experiment in solids. Many-spin clusters and correlations are created
faster in such experiments than in the usual MQ NMR experiments and can be used
for the investigation of many-spin dynamics of nuclear spins in solids.Comment: 11 pages, 3 figures. accepted for publication in Physical Review
Perturbation theorems for Hele-Shaw flows and their applications
In this work, we give a perturbation theorem for strong polynomial solutions
to the zero surface tension Hele-Shaw equation driven by injection or suction,
so called the Polubarinova-Galin equation. This theorem enables us to explore
properties of solutions with initial functions close to but are not polynomial.
Applications of this theorem are given in the suction or injection case. In the
former case, we show that if the initial domain is close to a disk, most of
fluid will be sucked before the strong solution blows up. In the later case, we
obtain precise large-time rescaling behaviors for large data to Hele-Shaw flows
in terms of invariant Richardson complex moments. This rescaling behavior
result generalizes a recent result regarding large-time rescaling behavior for
small data in terms of moments. As a byproduct of a theorem in this paper, a
short proof of existence and uniqueness of strong solutions to the
Polubarinova-Galin equation is given.Comment: 25 page
Efficient production of polar molecular Bose-Einstein condensates via an all-optical R-type atom-molecule adiabatic passage
We propose a scheme of "-type" photoassociative adiabatic passage (PAP) to
create polar molecular condensates from two different species of ultracold
atoms. Due to the presence of a quasi-coherent population trapping state in the
scheme, it is possible to associate atoms into molecules with a
\textit{low-power} photoassociation (PA) laser. One remarkable advantage of our
scheme is that a tunable atom-molecule coupling strength can be achieved by
using a time-dependent PA field, which exhibits larger flexibility than using a
tunable magnetic field. In addition, our results show that the PA intensity
required in the "-type" PAP could be greatly reduced compared to that in a
conventional "-type" one.Comment: 17 pages, 5 figures, to appear in New Journal of Physic
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