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Numerical Study Of The Three-Dimensional Random-Field Ising Model At Zero And Positive Temperature, Y Wu, Jonathan Machta
Numerical Study Of The Three-Dimensional Random-Field Ising Model At Zero And Positive Temperature, Y Wu, Jonathan Machta
Physics Department Faculty Publication Series
In this paper the three-dimensional random-field Ising model is studied at both zero temperature and positive temperature. Critical exponents are extracted at zero temperature by finite size scaling analysis of large discontinuities in the bond energy. The heat capacity exponent α is found to be near zero. The ground states are determined for a range of external field and disorder strength near the zero temperature critical point and the scaling of ground state tilings of the field-disorder plane is discussed. At positive temperature the specific heat and the susceptibility are obtained using the Wang-Landau algorithm. It is found that sharp …
Worm Algorithm For Continuous-Space Path Integral Monte Carlo Simulations, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Worm Algorithm For Continuous-Space Path Integral Monte Carlo Simulations, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
We present a new approach to path integral Monte Carlo (PIMC) simulations based on the worm algorithm, originally developed for lattice models and extended here to continuous-space many-body systems. The scheme allows for efficient computation of thermodynamic properties, including winding numbers and off-diagonal correlations, for systems of much greater size than that accessible to conventional PIMC simulations. As an illustrative application of the method, we simulate the superfluid transition of 4He in two dimensions.
Vortex-Phonon Interaction In The Kosterlitz-Thouless Theory, E Kozik, Nikolai Prokof'ev, Boris Svistunov
Vortex-Phonon Interaction In The Kosterlitz-Thouless Theory, E Kozik, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
The “canonical” variables of the Kosterlitz-Thouless theory—fields Φ0(r) and φ(r), generally believed to stand for vortices and phonons (or their XY equivalents, like spin waves, etc.) turn out to be neither vortices and phonons, nor, strictly speaking, canonical variables. The latter fact explains paradoxes of (i) absence of interaction between Φ0 and φ, and (ii) nonphysical contribution of small vortex pairs to long-range phase correlations. We resolve the paradoxes by explicitly relating Φ0 and φ to canonical vortex-pair and phonon variables.
Superglass Phase Of 4he, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Superglass Phase Of 4he, M Boninsegni, Nikolai Prokof'ev, Boris Svistunov
Physics Department Faculty Publication Series
We study different solid phases of 4He, by means of path integral Monte Carlo simulations based on a recently developed worm algorithm. Our study includes simulations that start off from a high-T gas phase, which is then “quenched” down to T=0.2 K. The low-T properties of the system crucially depend on the initial state. While an ideal hcp crystal is a clear-cut insulator, the disordered system freezes into a superglass, i.e., a metastable amorphous solid featuring off-diagonal long-range order and superfluidity.
Decoherence And Quantum Walks: Anomalous Diffusion And Ballistic Tails, Nikolai Prokof'ev, P.C.E Stamp
Decoherence And Quantum Walks: Anomalous Diffusion And Ballistic Tails, Nikolai Prokof'ev, P.C.E Stamp
Physics Department Faculty Publication Series
The common perception is that strong coupling to the environment will always render the evolution of the system density matrix quasiclassical (in fact, diffusive) in the long time limit. We present here a counterexample, in which a particle makes quantum transitions between the sites of a d-dimensional hypercubic lattice while strongly coupled to a bath of two-level systems that “record” the transitions. The long-time evolution of an initial wave packet is found to be most unusual: the mean square displacement of the particle density matrix shows long-range ballistic behavior, with ⟨n2⟩∼t2, but simultaneously a kind of weakly localized behavior near …
The Origin Of The Phase In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
The Origin Of The Phase In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe
Physics Department Faculty Publication Series
We consider the interference of two overlapping ideal Bose-Einstein condensates. The usual description of this phenomenon involves the introduction of a condensate wave function with a definite phase. We investigate the origin of this phase and the theoretical basis of treating interference. It is possible to construct a phase state for which the particle number is uncertain, but the phase is known. How such a state would be prepared before an experiment is not obvious. We show that a phase can also arise from experiments using condensates with known particle numbers. The analysis of measurements in such states also gives …