Biomedical subjects

Leonid P Pryadko

Publications and source records attributed to Leonid P Pryadko.

6 recordsLinked to original sources

PubMed2006

Heterogeneities and topological defects in two-dimensional pinned liquids.

We simulate a model of repulsively interacting colloids on a commensurate two-dimensional triangular pinning substrate where the amount of heterogeneous motion that appears at melting can be controlled systematically by turning off a fraction of the pinning sites. We correlate the amount of heterogeneous motion with the average topological defect number, time-dependent defect fluctuations, colloid diffusion, and the form of the van Hove correlation function. When the pinning sites are all off or all on, the melting occurs in a single step. When a fraction of the sites are turned off, the melting becomes considerably broadened and signatures of a two-step melting process appear. The noise power associated with fluctuations in the number of topological defects reaches a maximum when half of the pinning sites are removed and the noise spectrum has a pronounced 1 / f(alpha) structure in the heterogeneous regime. We find that regions of high mobility are associated with regions of high dislocation densities.

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PubMed2005

Quantum phase slips in the presence of finite-range disorder.

To study the effect of disorder on quantum phase slips (QPSs) in superconducting wires, we consider the plasmon-only model where disorder can be incorporated into a first-principles instanton calculation. We consider weak but general finite-range disorder and compute the form factor in the QPS rate associated with momentum transfer. We find that the system maps onto dissipative quantum mechanics, with the dissipative coefficient controlled by the wave (plasmon) impedance Z of the wire and with a superconductor-insulator transition at Z = 6.5 k. We speculate that the system will remain in this universality class after resistive effects at the QPS core are taken into account.

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PubMed2005

Driven classical diffusion with strong correlated disorder.

For driven classical diffusion quenched by a strong potential disorder V(x), we identify a prominent crossover regime between the regimes of very small and very large driving forces F, where the corresponding mobility values mu (F) differ exponentially. For disorder with power-law correlations at large distances 0, the crossover is characterized by power-law dependence of the logarithm of mu (F) on the driving force ln mu (F) approximately F(n/(n + 1)). For finite-range disorder (formally, n = infinity), the corresponding dependence is linear ("logarithmic susceptibility").

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PubMed2005

Scalable design of tailored soft pulses for coherent control.

We present a scalable scheme to design optimized soft pulses and pulse sequences for coherent control of interacting quantum many-body systems. The scheme is based on the cluster expansion and the time-dependent perturbation theory implemented numerically. This approach offers a dramatic advantage in numerical efficiency, and it is also more convenient than the commonly used Magnus expansion, especially when dealing with higher-order terms. We illustrate the scheme by designing 2nd-order self-refocusing pi pulses and a 6th-order 8-pulse refocusing sequence for a chain of qubits with nearest-neighbor couplings. We also discuss the performance of soft-pulse refocusing sequences in suppressing decoherence due to low-frequency environment.

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PubMed2005

Supersolids versus phase separation in two-dimensional lattice bosons.

We study the nature of the ground state of the two-dimensional extended boson Hubbard model on a square lattice by quantum Monte Carlo methods. We demonstrate that strong but finite on-site interaction U along with a comparable nearest-neighbor repulsion V result in a thermodynamically stable supersolid ground state for densities larger than 1/2, in contrast to fillings less than 1/2 or for very large U, where the checkerboard supersolid is unstable towards phase separation. We discuss the relevance of our results to realizations of supersolids using cold bosonic atoms in optical lattices.

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PubMed2004

Incipient order in the t-J model at high temperatures.

We analyze the high-temperature behavior of the susceptibilities towards a number of possible ordered states in the t-J-V model using the high-temperature series expansion. From all diagrams with up to ten edges, reliable results are obtained down to temperatures of order J, or (with some optimism) to J/2. In the unphysical regime, t J, these susceptibilities are small and decreasing with decreasing temperature; this suggests that the t-J model does not support high-temperature superconductivity. We also find modest evidence of a tendency toward nematic and d-density wave orders.

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