Svistunov, Boris

Job Title

Professor, Physics Department

Last Name

Svistunov

First Name

Boris

Discipline

Physics

Expertise

Theoretical Condensed Matter Physics

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Now showing 1 - 10 of 66

Exact quantum Monte Carlo process for the statistics of discrete systems
(1996) Prokof'ev, Nikolai; Svistunov, Boris; Tupitsyn, I
We propose an exact Monte Carlo approach for the statistics of discrete quantum systems that does not employ the standard partition of the imaginary time into a mesh and does not contain small parameters. The method operates with discrete objects — kinks, describing virtual transitions at different moments in time. The global statistics of the kinks is reproduced by exact local procedures, the main one being based on the known solution for an asymmetric two-level system.
Truncated-Determinant Diagrammatic Monte Carlo for Fermions with Contact Interaction
(2004-01-01) Bourovski, E; Prokof'ev, Nikolai; Svistunov, Boris
For some models of interacting fermions the known solution to the notorious sign problem in Monte Carlo (MC) simulations is to work with macroscopic fermionic determinants; the price, however, is a macroscopic scaling of the numerical effort spent on elementary local updates. We find that the ratio of two macroscopic determinants can be found with any desired accuracy by considering truncated (local in space and time) matices. In this respect, MC for interacting fermionic systems becomes similar to that for the sign-problem-free bosonic systems with system-size independent update cost. We demonstrate the utility of the truncated-determinant method by simulating the attractive Hubbard model within the MC scheme based on partially summed Feynman diagrams. We conjecture that similar approach may be useful in other implementations of the sign-free determinant schemes.
Superfluid-Insulator Transition in a Commensurate One-Dimensional Bosonic System with Off-Diagonal Disorder
(2005-01-01) Balabanyan, K; Prokof'ev, Nikolai; Svistunov, Boris
We study the nature of the superfluid-insulator quantum phase transition in a one-dimensional system of lattice bosons with off-diagonal disorder in the limit of a large integer filling factor. Monte Carlo simulations of two strongly disordered models show that the universality class of the transition in question is the same as that of the superfluid-Mott-insulator transition in a pure system. This result can be explained by disorder self-averaging in the superfluid phase and the applicability of the standard quantum hydrodynamic action. We also formulate the necessary conditions which should be satisfied by the stong-randomness universality class, if one exists.
Diagrammatic Monte Carlo
(2008-01-01) Houcke, K; Kozik, E; Prokof'ev, Nikolai; Svistunov, Boris
Diagrammatic Monte Carlo (DiagMC) is a numeric technique that allows one to calculate quantities specified in terms of diagrammatic expansions, the latter being a standard tool of many-body quantum statistics. The sign problem that is typically fatal to Monte Carlo approaches, appears to be manageable with DiagMC. Starting with a general introduction to the principles of DiagMC, we present a detailed description of the DiagMC scheme for interacting fermions (Hubbard model), as well as the first illustrative results for the equations of state.
Superfluid-Insulator Transition in Commensurate Disordered Bosonic Systems: Large-Scale Worm Algorithm Simulations
(2004-01-01) Prokof'ev, Nikolai; Svistunov, Boris
We report results of large-scale Monte Carlo simulations of superfluid-insulator transitions in disordered commensurate 2D bosonic systems. In the off-diagonal disorder case, we find that the transition is to a gapless incompressible insulator, and its dynamical critical exponent is z=1.5(2). In the diagonal-disorder case, we prove the conjecture that rare statistical fluctuations are inseparable from critical fluctuations on the largest scales and ultimately result in crossover to the generic universality class (apparently with z=2). However, even at strong disorder, the universal behavior sets in only at very large space-time distances. This explains why previous studies of smaller clusters mimicked a direct superfluid–Mott-insulator transition.
Monte Carlo study of the two-dimensional Bose-Hubbard model
(2008-01-01) Capogrosso-Sansone, B; Söyler, S; Prokof'ev, Nikolai; Svistunov, Boris
One of the most promising applications of ultracold gases in optical lattices is the possibility to use them as quantum emulators of more complex condensed matter systems. We provide benchmark calculations, based on exact quantum Monte Carlo simulations, for the emulator to be tested against. We report results for the ground state phase diagram of the two-dimensional Bose-Hubbard model at unity filling factor. We precisely trace out the critical behavior of the system and resolve the region of small insulating gaps, Δ⪡J. The critical point is found to be (J/U)c=0.05974(3), in perfect agreement with the high-order strong-coupling expansion method of Elstner and Monien [Phys. Rev. B 59, 12184 (1999)]. In addition, we present data for the effective mass of particle and hole excitations inside the insulating phase and obtain the critical temperature for the superfluid-normal transition at unity filling factor.
Luttinger Liquid in the Core of a Screw Dislocation in Helium-4
(2007-01-01) Boninsegni, M; Kuklov,; Pollet,; Prokof'ev, Nikolai; Svistunov, Boris; Troyer,
On the basis of first-principles Monte Carlo simulations we find that the screw dislocation along the hexagonal axis of an hcp 4He crystal features a superfluid (at T→0) core. This is the first example of a regular quasi-one-dimensional supersolid—the phase featuring both translational and superfluid orders, and one of the cleanest cases of a Luttinger-liquid system. In contrast, the same type of screw dislocation in solid H2 is insulating.
Superglass Phase of 4He
(2006-01-01) Boninsegni, M; Prokof'ev, Nikolai; Svistunov, Boris
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.
Superfluid-insulator and roughening transitions in domain walls
(2007-01-01) Söyler, S; Capogrosso-Sansone,; Prokof'ev, Nikolai; Svistunov, Boris
We have performed quantum Monte Carlo simulations to investigate the superfluid behavior of one- and two-dimensional interfaces separating checkerboard solid domains. The system is described by the hard-core Bose-Hubbard Hamiltonian with nearest-neighbor interaction. In accordance with Burovski et al. [Phys. Rev. Lett. 94, 165301 (2005)] we find that (i) the interface remains superfluid in a wide range of interaction strength before it undergoes a superfluid-insulator transition; (ii) in one dimension, the transition is of the Kosterlitz-Thouless type and is accompanied by the roughening transition, driven by proliferation of charge-1∕2 quasiparticles; (iii) in two dimensions, the transition belongs to the three-dimensional U(1) universality class and the interface remains smooth. Similar phenomena are expected for domain walls in quantum antiferromagnets.
Bold Diagrammatic Monte Carlo Technique: When the Sign Problem Is Welcome
(2007-01-01) Prokof'ev, N; Svistunov, B
We introduce a Monte Carlo scheme for sampling a bold-line diagrammatic series specifying an unknown function in terms of itself. The range of convergence of this bold(-line) diagrammatic Monte Carlo (BMC) technique is significantly broader than that of a simple iterative scheme for solving integral equations. With the BMC technique, a moderate “sign problem” turns out to be an advantage in terms of the convergence of the process. For an illustrative purpose, we solve the one-particle s-scattering problem. As an important application, we obtain the T matrix for a Fermi polaron (one spin-down particle interacting with the spin-up fermionic sea).