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Microcanonical Monte Carlo simulations for the two-dimensional XY model

S. B. Ota, S. B. Ota, M. Fähnle

The authors have carried out microcanonical Monte Carlo (MC) simulations for the two-dimensional (2D) classical XY model on a square lattice having 900 spins with periodic boundary conditions. The temperature dependence of the energy, specific heat, mean-square magnetization and vortex density show good agreement with the existing canonical MC simulation results. They thus demonstrate ergodicity in the microcanonical MC simulations for the 2D classical XY model. The maximum of the temperature derivative of the vortex density is found to occur at the temperature corresponding to the maximum of the specific heat.The authors have carried out microcanonical Monte Carlo (MC) simulations for the two-dimensional (2D) classical XY model on a square lattice having 900 spins with periodic boundary conditions. The temperature dependence of the energy, specific heat, mean-square magnetization and vortex density show good agreement with the existing canonical MC simulation results. They thus demonstrate ergodicity in the microcanonical MC simulations for the 2D classical XY model. The maximum of the temperature derivative of the vortex density is found to occur at the temperature corresponding to the maximum of the specific heat.

Journal of Physics Condensed MatterJun 15, 199219 citations

Flux noise in SQUIDs: Electron versus nuclear spins

Rogério de Sousa, S. LaForest

Bulletin of the American Physical SocietyMar 2, 20150 citations

Low-frequency Flux Noise in SQUIDs and Superconducting Qubits

S. Sendelbach, David J. Hover, A. Kittel +2 more

Bulletin of the American Physical SocietyMar 11, 20080 citations

Candidate Source of Flux Noise in SQUIDs: Adsorbed Oxygen Molecules

Hui Wang, Chuntai Shi, Jun Hu +3 more

A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O_{2} molecules adsorbed on the surface. Using density functional theory calculations, we find that an O_{2} molecule adsorbed on an α-alumina surface has a magnetic moment of ~1.8 μ_{B}. The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic XY spins on a square lattice find 1/f magnetization noise, consistent with flux noise in Al SQUIDs.A major obstacle to using superconducting quantum interference devices (SQUIDs) as qubits is flux noise. We propose that the heretofore mysterious spins producing flux noise could be O_{2} molecules adsorbed on the surface. Using density functional theory calculations, we find that an O_{2} molecule adsorbed on an α-alumina surface has a magnetic moment of ~1.8 μ_{B}. The spin is oriented perpendicular to the axis of the O-O bond, the barrier to spin rotations is about 10 mK. Monte Carlo simulations of ferromagnetically coupled, anisotropic XY spins on a square lattice find 1/f magnetization noise, consistent with flux noise in Al SQUIDs.

arXiv:1504.08075Physical Review LettersAug 14, 201559 citations

Dynamical phase transitions in the two-dimensional XY model

O. Golinelli, Bernard Derrida

The 2D XY model is studied by Monte Carlo simulations where two configurations subjected to the same thermal noise are compared. The authors observe three temperature regimes: a high-temperature phase where the two configurations meet, an intermediate phase where they do not meet but their distance becomes independent of the initial distance and a low-temperature phase where the distance remembers for very long the initial distance. The two transition temperatures T 1 =1.61+or-0.01 and T 2 =0.95+or-0.05 are estimated by means of finite-size scaling.The 2D XY model is studied by Monte Carlo simulations where two configurations subjected to the same thermal noise are compared. The authors observe three temperature regimes: a high-temperature phase where the two configurations meet, an intermediate phase where they do not meet but their distance becomes independent of the initial distance and a low-temperature phase where the distance remembers for very long the initial distance. The two transition temperatures T 1 =1.61+or-0.01 and T 2 =0.95+or-0.05 are estimated by means of finite-size scaling.

Journal of Physics A Mathematical and GeneralOct 7, 198929 citations

Investigation of 1/f flux noise in SQUIDs and Superconducting Qubits

Antonio Puglielli, S. Sendelbach, Taylor Klaus +1 more

Bulletin of the American Physical SocietyMar 19, 20130 citations

Estimation of Mean Square Flux Noise in SQUIDs from Monte Carlo Simulations of the Classical 2D XY Model

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Estimation of Mean Square Flux Noise in SQUIDs from Monte Carlo Simulations of the Classical 2D XY Model

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