Quantum Computing with Cold Ions and Atoms: Theory
Chapter in Quantum Information, Wiley (2016) 483-517
Exact inference on Gaussian graphical models of arbitrary topology using path-sums
Journal of Machine Learning Research Journal of Machine Learning Research 17:71 (2016) 1-19
Abstract:
We present the path-sum formulation for exact statistical inference of marginals on Gaussian graphical models of arbitrary topology. The path-sum formulation gives the covariance between each pair of variables as a branched continued fraction of finite depth and breadth. Our method originates from the closed-form resummation of infinite families of terms of the walk-sum representation of the covariance matrix. We prove that the path-sum formulation always exists for models whose covariance matrix is positive definite: i.e. it is valid for both walk-summable and non-walk-summable graphical models of arbitrary topology. We show that for graphical models on trees the path-sum formulation is equivalent to Gaussian belief propagation. We also recover, as a corollary, an existing result that uses determinants to calculate the covariance matrix. We show that the path-sum formulation formulation is valid for arbitrary partitions of the inverse covariance matrix. We give detailed examples demonstrating our results.Possible light-induced superconductivity in K3C60 at high temperature
Nature Nature Publishing Group 530:2016 (2016) 461-464
Abstract:
The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4, 5, 6). This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.Beyond mean-field bistability in driven-dissipative lattices: Bunching-antibunching transition and quantum simulation
Physical Review A American Physical Society (APS) 93:2 (2016) 023821
Connected correlations, fluctuations and current of magnetization in the steady state of boundary driven XXZ spin chains
Journal of Statistical Mechanics Theory and Experiment IOP Publishing 2016:2 (2016) 023102