DSpace Collection:https://dspace.lboro.ac.uk/2134/11342015-07-31T09:24:09Z2015-07-31T09:24:09ZSuperlight small bipolarons in the presence of strong Coulomb repulsionHague, J.P.Kornilovitch, P.E.Samson, J.H.Alexandrov, A.S.https://dspace.lboro.ac.uk/2134/27482013-01-22T23:43:20Z2007-01-01T00:00:00ZTitle: Superlight small bipolarons in the presence of strong Coulomb repulsion
Authors: Hague, J.P.; Kornilovitch, P.E.; Samson, J.H.; Alexandrov, A.S.
Abstract: We study a lattice bipolaron on a staggered triangular ladder and triangular and hexagonal lattices with both long-range electron-phonon interaction and strong Coulomb repulsion using a novel continuous-time quantum Monte-Carlo (CTQMC) algorithm extended to the Coulomb-Frohlich model with two particles. The algorithm is preceded by an exact integration over phonon degrees of freedom, and as such is extremely efficient. The bipolaron effective mass and bipolaron radius are computed. Lattice bipolarons on such lattices have a novel crablike motion, and are small but very light in a wide range of parameters, which leads to a high Bose-Einstein condensation temperature. We discuss the relevance of our results with current experiments on cuprate high-temperature superconductors and propose a route to room temperature superconductivity.
Description: This is a pre-print of an article to be published in the journal, Physics Review Letters. It is also available at: http://uk.arxiv.org/abs/cond-mat/06060362007-01-01T00:00:00ZCoherent-state path-integral calculation of the Wigner functionSamson, J.H.https://dspace.lboro.ac.uk/2134/22302013-01-22T23:37:17Z2000-01-01T00:00:00ZTitle: Coherent-state path-integral calculation of the Wigner function
Authors: Samson, J.H.
Description: This is a pre-print. The definitive version: SAMSON (2000)Coherent-state path-integral calculation of the Wigner function. Journal of Physics A: Mathematical and General, 33(29), pp. 5219-5229, and is available at: http://www.iop.org/EJ/journal/JPhysA.2000-01-01T00:00:00ZPhase-space path-integral calculation of the Wigner functionSamson, J.H.https://dspace.lboro.ac.uk/2134/22292013-01-22T23:44:11Z2003-01-01T00:00:00ZTitle: Phase-space path-integral calculation of the Wigner function
Authors: Samson, J.H.
Abstract: The Wigner function W(q,p) is formulated as a phase-space path integral, whereby its sign oscillations can be seen to follow from interference between the geometrical phases of the paths. The approach has similarities to the path-centroid method in the configuration-space path integral. Paths can be classified by the mid-point of their ends; short paths where the mid-point is close to (q,p) and which lie in regions of low energy (low P function of the Hamiltonian) will dominate, and the enclosed area will determine the sign of the Wigner function. As a demonstration, the method is applied to a sequence of density matrices interpolating between a Poissonian number distribution and a number state, each member of which can be represented exactly by a discretized path integral with a finite number of vertices. Saddle point evaluation of these integrals recovers (up to a constant factor) the WKB approximation to the Wigner function of a number state.
Description: This is a pre-print. The definitive version: SAMSON (2003), Phase-space path-integral calculation of the Wigner function. Journal of Physics A: Mathematical and General, 36, 10637 - 10650, is available at: http://www.iop.org/EJ/journal/JPhysA.2003-01-01T00:00:00ZBuckyball quantum computer: realization of a quantum gateGarelli, M.S.Kusmartsev, F.V.https://dspace.lboro.ac.uk/2134/21222013-01-09T23:34:00Z2005-01-01T00:00:00ZTitle: Buckyball quantum computer: realization of a quantum gate
Authors: Garelli, M.S.; Kusmartsev, F.V.
Abstract: We have studied a system composed by two endohedral fullerene molecules. We have found that
this system can be used as good candidate for the realization of Quantum Gates. Each of these molecules
encapsules an atom carrying a spin, therefore they interact through the spin dipole interaction. We show
that a phase gate can be realized if we apply static and time dependent magnetic fields on each encased
spin. We have evaluated the operational time of a pi-phase gate, which is of the order of ns. We made a
comparison between the theoretical estimation of the gate time and the experimental decoherence time for
each spin. The comparison shows that the spin relaxation time is much larger than the pi-gate operational
time. Therefore, this indicates that, during the decoherence time, it is possible to perform some thousands
of quantum computational operations. Moreover, through the study of concurrence, we get very good
results for the entanglement degree of the two-qubit system. This finding opens a new avenue for the
realization of Quantum Computers.
Description: This is a pre-print. It is also available at: http://arxiv.org/abs/quant-ph/0501076.2005-01-01T00:00:00Z