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Boris Svistunov

Publications and source records attributed to Boris Svistunov.

80 records · Page 5Linked to original sources
arXiv2002

Two-Dimensional Weakly Interacting Bose Gas in the Fluctuation Region

We study the crossover between the mean-field and critical behavior of the two-dimensional Bose gas throughout the fluctuation region of the Berezinskii--Kosterlitz--Thouless phase transition point. We argue that this crossover is described by universal (for all weakly interacting |psi|^4 models) relations between thermodynamic parameters of the system, including superfluid and quasi-condensate densities. We establish these relations with high-precision Monte Carlo simulations of the classical |psi|^4 model on a lattice, and check their asymptotic forms against analytic expressions derived on the basis of the mean-field theory.

cond-mat↗
arXiv2001

Critical Point of a Weakly Interacting Two-Dimensional Bose Gas

We study the Berezinskii-Kosterlitz-Thouless transition in a weakly interacting 2D quantum Bose gas using the concept of universality and numerical simulations of the classical $|ψ|^4$-model on a lattice. The critical density and chemical potential are given by relations $n_c=(mT/2π\hbar^2) \ln(ξ\hbar^2/ mU)$ and $μ_c=(mTU/π\hbar^2) \ln(ξ_μ \hbar^2/ mU)$, where $T$ is the temperature, $m$ is the mass, and $U$ is the effective interaction. The dimensionless constant $ξ= 380 \pm 3$ is very large and thus any quantitative analysis of the experimental data crucially depends on its value. For $ξ_μ$ our result is $ξ_μ = 13.2 \pm 0.4 $. We also report the study of the quasi-condensate correlations at the critical point.

cond-mat↗
arXiv2001

Critical Temperature Shift in Weakly Interacting Bose Gas

With a high-performance Monte Carlo algorithm we study the interaction-induced shift of the critical point in weakly interacting three-dimensional $|ψ|^4$-theory (which includes quantum Bose gas). In terms of critical density, $n_c$, mass, $m$, interaction, $U$, and temperature, $T$, this shift is universal: $Δn_c(T) = - C m^3 T^2 U$, the constant $C$ found to be equal to $0.0140 \pm 0.0005$. For quantum Bose gas with the scattering length $a$ this implies $ΔT_c/T_c = C_0 a n^{1/3}$, with $C_0=1.29 \pm 0.05$.

cond-mat↗
arXiv2001

Worm algorithms for classical statistical models

We show that high-temperature expansions may serve as a basis for the novel approach to efficient Monte Carlo simulations. "Worm" algorithms utilize the idea of updating closed path configurations (produced by high-temperature expansions) through the motion of end points of a disconnected path. An amazing result is that local, Metropolis-type schemes may have dynamical critical exponents close to zero (i.e., their efficiency is comparable to the best cluster methods). We demonstrate this by calculating finite size scaling of the autocorrelation time for various (six) universality classes.

cond-mat↗
arXiv2000

Kinetics of Strongly Non-Equilibrium Bose-Einstein Condensation

We consider the ordering kinetics in a strongly non-equilibrium state of a (weakly) interacting Bose gas, characterized, on one hand, by large occupation numbers, and, on the other hand, by the absence of long-range order. Up to higher-order corrections in inverse occupation numbers, the evolution is described by non-linear Schrodinger equation with a turbulent initial state. The ordering process is rather rich and involves a number of qualitatively different regimes that take place in different regions of energy space. Specially addressed is the case of evolution in an external potential.

cond-mat↗
arXiv2000

Strongly Non-Equilibrium Bose-Einstein Condensation in a Trapped Gas

We present a qualitative (and quantitative, at the level of estimates) analysis of the ordering kinetics in a strongly non-equilibrium state of a weakly interacting Bose gas, trapped with an external potential. At certain conditions, the ordering process is predicted to be even more rich than in the homogeneous case. Like in the homogeneous case, the most characteristic feature of the full-scale non-equilibrium process is the formation of superfluid turbulence.

cond-mat↗
arXiv1999

Tunneling problems by quantum Monte Carlo

We develop a new numerical scheme which allows precise solution of coherent tunneling problems, i.e., problems with exponentially small transition amplitudes between quasidegenerate states. We explain how this method works for the single-particle (tunneling in the double-well potential) and many-body systems (e.g., vacuum-to-vacuum transitions), and gives directly the instanton shape and tunneling amplitude. Most importantly, transition amplitudes may be calculated to arbitrary accuracy (being limited solely by statistical errors) no matter how small are their absolute values.

cond-mat↗