Biomedical subjects

V B Geshkenbein

Publications and source records attributed to V B Geshkenbein.

6 recordsLinked to original sources

PubMed2005

Dissociation of vortex stacks into fractional-flux vortices.

We discuss the zero field superconducting phase transition in a finite system of magnetically coupled superconducting layers. Transverse screening is modified by the presence of other layers resulting in topological excitations with fractional flux. Vortex stacks trapping a full flux and present at any finite temperature undergo a dissociation transition which corresponds to the depairing of fractional-flux vortices in individual layers. We propose an experiment with a bilayer system allowing us to identify the dissociation of bound vortex molecules.

Journal Article↗

PubMed2004

Decoherence in superconducting quantum bits by phonon radiation.

We discuss a fundamental limitation for the coherent operation of superconducting quantum bits originating from phonon radiation generated in the Josephson junctions of the device. The time dependent superconducting phase across the junction produces an electric field that couples to the underlying crystal lattice via the piezoelectric effect. We determine the radiation resistance of the junction due to phonon emission and derive substantial decoherence rates for the quantum bits, which are compatible with quality factors measured in recent experiments.

Journal Article↗

PubMed2004

Superconducting tetrahedral quantum bits.

We propose a design for a qubit with four superconducting islands in the topology of a symmetric tetrahedron, uniformly frustrated with one-half flux quantum per loop and one-half Cooper pair per island. This structure emulates a noise-resistant spin-1/2 system in a vanishing magnetic field. The flux frustration boosts quantum fluctuations and relieves the constraints on junction fabrication. Variability of manipulation and optimized readout are additional benefits of this design.

Journal Article↗

PubMed2004

Weak to strong pinning crossover.

Material defects in hard type II superconductors pin the flux lines and thus establish the dissipation-free current transport in the presence of a finite magnetic field. Depending on the density and pinning force of the defects and the vortex density, pinning is either weak collective or strong. We analyze the weak to strong pinning crossover of vortex matter in disordered superconductors and discuss the peak effect appearing naturally in this context.

Journal Article↗

PubMed2004

Quantum fluctuations in thin superconducting wires of finite length.

In one-dimensional wires, fluctuations destroy superconducting long-range order and stiffness at finite temperatures; in an infinite wire, quasi-long-range order and stiffness survive at zero temperature if the wire's dimensionless admittance mu is large, mu>2. We analyze the disappearance of this superconductor-insulator quantum phase transition in a finite wire and its resurrection due to the wire's coupling to its environment characterized through the dimensionless conductance K.

Journal Article↗

PubMed2001

Superfluidity versus Bloch oscillations in confined atomic gases.

We study the superfluid properties of (quasi) one-dimensional bosonic atom gases/liquids in traps with finite geometries in the presence of strong quantum fluctuations. Driving the condensate with a moving defect we find the nucleation rate for phase slips using instanton techniques. While phase slips are quenched in a ring resulting in a superfluid response, they proliferate in a tube geometry where we find Bloch oscillations in the chemical potential. These Bloch oscillations describe the individual tunneling of atoms through the defect and thus are a consequence of particle quantization.

Journal Article↗