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 nnary 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 $0,1,..., n-1$, 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 $nth$ energy band is a linear superposition of Mathieu's functions $ce_{n-1}$ and $se_n$; and the Bloch wave in the $nth$ band gap is a linear superposition of $ce_n$ and $se_n$. 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