46,028 research outputs found
A More Precise Extraction of |V_{cb}| in HQEFT of QCD
The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure
One Dimensional ary Density Classification Using Two Cellular Automaton Rules
Suppose each site on a one-dimensional chain with periodic boundary condition
may take on any one of the states , can you find out the most
frequently occurring state using cellular automaton? Here, we prove that while
the above density classification task cannot be resolved by a single cellular
automaton, this task can be performed efficiently by applying two cellular
automaton rules in succession.Comment: Revtex, 4 pages, uses amsfont
Localized gap soliton trains of Bose-Einstein condensates in an optical lattice
We develop a systematic analytical approach to study the linear and nonlinear
solitary excitations of quasi-one-dimensional Bose-Einstein condensates trapped
in an optical lattice. For the linear case, the Bloch wave in the energy
band is a linear superposition of Mathieu's functions and ;
and the Bloch wave in the band gap is a linear superposition of
and . For the nonlinear case, only solitons inside the band gaps are
likely to be generated and there are two types of solitons -- fundamental
solitons (which is a localized and stable state) and sub-fundamental solitons
(which is a lacalized but unstable state). In addition, we find that the
pinning position and the amplitude of the fundamental soliton in the lattice
can be controlled by adjusting both the lattice depth and spacing. Our
numerical results on fundamental solitons are in quantitative agreement with
those of the experimental observation [Phys. Rev. Lett. {\bf92}, 230401
(2004)]. Furthermore, we predict that a localized gap soliton train consisting
of several fundamental solitons can be realized by increasing the length of the
condensate in currently experimental conditions.Comment: 9 pages, 6 figures, accepted for publicaiton in PR
Exploring the quantum critical behaviour in a driven Tavis-Cummings circuit
Quantum phase transitions play an important role in many-body systems and
have been a research focus in conventional condensed matter physics over the
past few decades. Artificial atoms, such as superconducting qubits that can be
individually manipulated, provide a new paradigm of realising and exploring
quantum phase transitions by engineering an on-chip quantum simulator. Here we
demonstrate experimentally the quantum critical behaviour in a
highly-controllable superconducting circuit, consisting of four qubits coupled
to a common resonator mode. By off-resonantly driving the system to renormalise
the critical spin-field coupling strength, we have observed a four-qubit
non-equilibrium quantum phase transition in a dynamical manner, i.e., we sweep
the critical coupling strength over time and monitor the four-qubit scaled
moments for a signature of a structural change of the system's eigenstates. Our
observation of the non-equilibrium quantum phase transition, which is in good
agreement with the driven Tavis-Cummings theory under decoherence, offers new
experimental approaches towards exploring quantum phase transition related
science, such as scaling behaviours, parity breaking and long-range quantum
correlations.Comment: Main text with 3 figure
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