Secure Quantum Secret Sharing Based on Reusable GHZ States as Secure Carriers

We show a potential eavesdropper can eavesdrop whole secret information when the legitimate users use secure carrier to encode and decode classical information repeatedly in the protocol [proposed in Bagherinezhad S and Karimipour V 2003 Phys. Rev. A \textbf{67} 044302]. Then we present a revised quantum secret sharing protocol by using Greenberger-Horne-Zeilinger state as secure carrier. Our protocol can resist Eve's attack

Collective excitations in double-layer quantum Hall systems

We study the collective excitation spectra of double-layer quantum-Hall systems using the single mode approximation. The double-layer in-phase density excitations are similar to those of a single-layer system. For out-of-phase density excitations, however, both inter-Landau-level and intra-Landau-level double-layer modes have finite dipole oscillator strengths. The oscillator strengths at long wavelengths for the latter transitions are shifted upward by interactions by identical amounts proportional to the interlayer Coulomb coupling. The intra-Landau-level out-of-phase mode has a gap when the ground state is incompressible except in the presence of spontaneous inter-layer coherence. We compare our results with predictions based on the Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page

Search for the \pi Resonance in Two Particle Tunneling Experiments of YBCO Superconductors

A recent theory of the resonant neutron scattering peaks in YBCO superconductors predicts the existence of a sharp spin triplet two particle collective mode (the ``\pi resonance") in the normal state. In this paper, we propose an experiment in which the \pi resonance could be probed directly in a two particle tunneling measurement.Comment: 10 pages, LATEX , 3 ps figure

Multi-Receiver Quantum Dense Coding with Non-Symmetric Quantum Channel

A two-receiver quantum dense coding scheme and an $N$-receiver quantum dense coding scheme, in the case of non-symmetric Hilbert spaces of the particles of the quantum channel, are investigated in this paper. A sender can send his messages to many receivers simultaneously. The scheme can be applied to quantum secret sharing and controlled quantum dense coding.Comment: To appear in Journal of the Korean Physical Societ

A new approach to bulk viscosity in strange quark matter at high densities

A new method is proposed to compute the bulk viscosity in strange quark matter at high densities. Using the method it is straightforward to prove that the bulk viscosity is positive definite, which is not so easy to accomplish in other approaches especially for multi-component fluids like strange quark matter with light up and down quarks and massive strange quarks.Comment: 7pages, talk given in SQM2008. Minor revisions, including clarification and updated reference

Dynamical Axion Field in Topological Magnetic Insulators

Axions are very light, very weakly interacting particles postulated more than 30 years ago in the context of the Standard Model of particle physics. Their existence could explain the missing dark matter of the universe. However, despite intensive searches, they have yet to be detected. In this work, we show that magnetic fluctuations of topological insulators couple to the electromagnetic fields exactly like the axions, and propose several experiments to detect this dynamical axion field. In particular, we show that the axion coupling enables a nonlinear modulation of the electromagnetic field, leading to attenuated total reflection. We propose a novel optical modulators device based on this principle.Comment: 5 pages, 3 figure

Finite-Size Studies on the SO(5) Symmetry of the Hubbard Model

We present numerical evidence for the approximate SO(5) symmetry of the Hubbard model on a 10 site cluster. Various dynamic correlation functions involving the $\pi$ operators, the generators of the SO(5) algebra, are studied using exact diagonalisation, and are found to possess sharp collective peaks. Our numerical results also lend support on the interpretation of the recent resonant neutron scattering peaks in the YBCO superconductors in terms of the Goldstone modes of the spontaneously broken SO(5) symmetry.Comment: 4 pages, Rev-Tex, includes 2 eps figure