89 research outputs found
Rederivation of the Casimir force under the completeness relation of continuum operator
Casimir effects manifests that, the two closely paralleled plates, generally
produce a macroscopic attractive force due to the quantum vacuum fluctuations
of the electromagnetic fields. The derivation of the force requires an {\it
artificial} regulator by removing the divergent summation. By including
naturally a spectrum density factor, based on the observation that an
incomplete eigenvectors of observable, such as the eigenstates for the photons
in the free field, can form a complete set of eigenvectors by introducing a
unique spectrum transformation, an alternative way is presented to rederive the
force, without using a regulator. As a result, the Casimir forces are obtained
with the first term attractive, and the second one,
, also attractive but smaller, with
the plate separation, and a to-be-determined small constant number in
the spectrum density factor.Comment: 5 page
Wave-packet trains of a time-dependent harmonic oscillator
By using a test-function method, we construct exact solutions of a
quantum harmonic oscillator with a time-dependent "spring constant". Any -th
solution describes a wave-packet train consisting of packets. Its center
oscillates like the classically harmonic oscillator with variable frequency,
and width and highness of each packet change simultaneously. When the
deformation is small, it behaves like a soliton train, and the large
deformation is identified with collapse and revival of the wave-packet train.Comment: 4 pages, 3 figure
The avalanche dynamics in Bak-Sneppen evolution model observed with standard distribution width of fitness
See the updated version arXiv:nlin/0111028.Comment: This paper has been withdrawn by the author due to a updated version
was submitte
Implementation for Solving Random Satisfiability Problems through CNOT-based circuits in a NMR Quantum Processor
We give a general method of construting quantum circuit for random
\QTR{it}{satisfiability} (SAT) problems with the basic logic gates such as
multi-qubit controlled-NOT and NOT gates. The sizes of these circuits are
almost the same as the sizes of the SAT formulas. Further, a parallelization
scheme is described to solve random SAT problems efficiently through these
quantum circuits in \QTR{it}{nuclear magnetic resonance} (NMR) ensemble quantum
computing. This scheme exploits truly mixed states as input states rather than
pseudo-pure states, and combines with the topological nanture of the NMR
spectrum to identify the solutions to SAT problems in a parallel way. Several
typical SAT problems have been experimentally demonstrated by this scheme with
good performances.Comment: 17 pages, 7 figure
Conditional Spontaneous Spin Polarization and Bifurcation Delay in Coupled Two-Component Bose-Einstein Condensates
The spontaneous spin polarization and bifurcation delay in two-component
Bose-Einstein condensates coupled with Raman pulses are investigated. We find
that the bifurcation and the spontaneous spin polarization depend not only on
the system parameters, but also on the relative phase between two components.
Through bifurcations, the system enters into the spontaneous spin polarization
regime from the Rabi regime. We also find that bifurcation delay appears when
the parameter is swept through the static bifurcation point. This bifurcation
delay is responsible for metastability leading to hysteresis. The area enclosed
in the hysteresis loop increases with the sweeping rate of the parameter.Comment: 10 pages, 3 figure
Experimental demonstration of the interferometric complementarity of one- and two-particle interference in a bulk Nuclear Magnetic Resonance ensemble
We analyze an interferometric complementarity between one- and two-particle
interference in the general case: , ,
and further examine the relation among one-particle interference visibility
, two-particle interference visibility and the predication
of the path of a single particle. An equality
, is achieved for any pure
two-particle source, which implies the condition of the complementarity
relation to reach the upper bound and its relation to another interferometric
complementarity between path information and interference visibility of a
single particle. Meanwhile, the relationships of the complementarities and the
entanglement of the composite system are also investigated. Using nuclear
magnetic resonance techniques, the two-particle interferometric complementarity
was experimentally tested with the ensemble-averaged spin states, including two
extreme cases and an intermediate case.Comment: 8 pages, 4 PS figure
Nuclear Magnetic Resonance Implemenations of Remote State Preparation of Arbitary Longitudinal Qubit and Remote State Measurement of a Qubit
A qubit chosen from equatorial or polar great circles on a Bloch sphere can
be remotely prepared with an Einstain-Podolsky-Rosen (EPR) state shared and a
cbit communication. We generalize this protocal into an arbitrary longitudinal
qubit on the Bloch sphere in which the azimuthal angle phi can be an arbitrary
value instead of only being zero. The generalized scheme was experimentally
realized using liquid-state nuclear magnetic resonance (NMR) techniques. Also,
we have experimentally demonstrated remote state measurement (RSM) on an
arbitary qubit proposed by Pati.Comment: 10 pages, 3 PS figure
Quantum computing by pairing trapped ultracold ions
The superpositional wave function oscillations for finite-time implementation
of quantum algorithms modifies the desired interference required for quantum
computing. We propose a scheme with trapped ultracold ion-pairs being qubits to
diminish the detrimental effect of the wave function oscillations, and apply
the scheme to the two-qubit Grover's search. It can be also found that the
qubits in our scheme are more robust against the decoherence caused by the
environment, and the model is scalable.Comment: 10 pages, no figure
Numerical Approach to the Evolution of the Spin-boson Systems and its Application on the Buck-Sukumar Model
We present a systematic numerical iteration approach to study the evolution
properties of the spin-boson systems, which works well in whole coupling
regime. This approach involves the evaluation of a set of coefficients for the
formal expansion of the time-dependent Schr\"{o}dinger equation by expanding the initial state in Fock space. The main advantage of this method is that this set
of coefficients is unique for the Hamiltonian studied, which allows one to
calculate the time evolution based on the different initial states. To
complement our numerical calculations, the method is applied to the
Buck-Sukumar model. Furthermore, we pointed out that, when the ground state
energy of the model is unbounded and no ground state exists in a certain
parameter space, the unstable time evolution of the physical quantities is the
natural results. Furthermore, we test the performance of the numerical method
to the Hamiltonian that use anti-Hermitian terms for modeling open quantum
systems.Comment: 8 pages, 6 figure
Condensate fraction of molecules for a spin mixture of ultracold fermionic atoms
The condensate fraction of molecules for ultracold Fermi gases is
investigated for the magnetic field below the Feshbach resonant magnetic field.
Assuming that there is no loss of particles and energy during the adiabatic
magnetic-field sweep, a simple theory is used to interpret the measured
condensate fraction in the experiments by JILA group (Phys. Rev. Lett. 92,
040403 (2004)) and MIT group (Phys. Rev. Lett. 92, 120403 (2004)). Our theory
shows that the condensate fraction of molecules is dependent on the initial
condition of the system and especially on the process of the magnetic-field
sweep.Comment: 4 pages, RevTex, 2 figs, E-mail: [email protected] A revised
version according to the comments and suggestions of the referee
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