Quantum Zeno effect in the Cooper-pair transport through a double-island Josephson system

Motivated by recent experiments, we analyze transport of Cooper pairs through a double-island Josephson qubit. At low bias in a certain range of gate voltages coherent superpositions of charge states play a crucial role. Analysis of the evolution of the density matrix allows us to cover a wide range of parameters, incl. situations with degenerate levels, when dissipation strongly affects the coherent eigenstates. At high noise levels the so-called Zeno effect can be observed, which slows down the transport. Our analysis explains certain features of the I-V curves, in particular the visibility and shape of resonant peaks and lines

Scenario for Ultrarelativistic Nuclear Collisions: Space--Time Picture of Quantum Fluctuations and the Birth of QGP

We study the dynamics of quantum fluctuations which take place at the earliest stage of high-energy processes and the conditions under which the data from e-p deep-inelastic scattering may serve as an input for computing the initial data for heavy-ion collisions at high energies. Our method is essentially based on the space-time picture of these seemingly different phenomena. We prove that the ultra-violet renormalization of the virtual loops does not bring any scale into the problem. The scale appears only in connection with the collinear cut-off in the evolution equations and is defined by the physical properties of the final state. In heavy-ion collisions the basic screening effect is due to the mass of the collective modes (plasmons) in the dense non-equilibrium quark-gluon system, which is estimated. We avoid the standard parton phenomenology and suggest a dedicated class of evolution equations which describe the dynamics of quantum fluctuations in heavy-ion collisions.Comment: 54 pages, 11 Postscript figures, uses RevTe

Nondemolition measurements of a single quantum spin using Josephson oscillations

We consider a Josephson junction containing a single localized spin 1/2 between conventional singlet superconducting electrodes. We study the spin dynamics and measurements when a dc-magnetic field ${\bf B}\parallel z$ acts on the spin and the junction is embedded into a dissipative circuit. We show that when tunneling or a voltage are turned on at time $t=0$ the Josephson current starts to oscillate with an amplitude depending on the initial ($t=0$) value of the spin $z$-component, $S_z= \pm 1/2$. At low temperatures, when effects of quasiparticles may be neglected, this procedure realizes a quantum-non-demolition (QND) measurement of $S_z$.Comment: 4 pages, 1 figure; average value of spin z operator changed to eigenvalue S_

Non-adiabatically detecting the geometric phase of the macroscopic quantum state with symmetric SQUID

We give a simple way to detect the geometric phase shift and the conditional geometric phase shift with Josephson junction system. Comparing with the previous work(Falcl G, Fazio R, Palma G.M., Siewert J and Verdal V, {\it Nature} {\bf 407}, 355(2000)), our scheme has two advantages. We use the non-adiabatic operation, thus the detection is less affected by the decoherence. Also, we take the time evolution on zero dynamic phase loop, we need not take any extra operation to cancel the dynamic phase.Comment: 8 pages, 4 figure

Direct Observation of Josephson Capacitance

The effective capacitance has been measured in the split Cooper pair box (CPB) over its phase-gate bias plane. Our low-frequency reactive measurement scheme allows to probe purely the capacitive susceptibility due to the CPB band structure. The data are quantitatively explained using parameters determined independently by spectroscopic means. In addition, we show in practice that the method offers an efficient way to do non-demolition readout of the CPB quantum state.Comment: 4 page

Theory of pairing symmetry inside the Abrikosov vortex core

We show that the Cooper pair wave function at the center of an Abrikosov vortex with vorticity m has different parity with respect to frequency from that in the bulk if m is an odd number and has the same parity if m is an even number. As a result, in a conventional vortex with m=1, the local density of states at the Fermi energy has a maximum (minimum) at the center of the vortex core in even(odd)-frequency superconductor. We propose a scanning tunneling microscope experiment using a superconducting tip to explore odd-frequency superconductivity.Comment: 5 pages, 3 figure

Vortex matter in the charged Bose liquid at absolute zero

The Gross-Pitaevskii-type equation is solved for the charge Bose liquid in the external magnetic field at zero temperature. There is a vortex lattice with locally broken charge neutrality. The boson density is modulated in real space and each vortex is charged. Remarkably, there is no upper critical field at zero temperature, so the density of single flux-quantum vortices monotonously increases with the magnetic field up to B=infinity and no indication of a phase transition. The size of each vortex core decreases as about 1/sqrt(B) keeping the system globally charge neutral. If bosons are composed of two fermions, a phase transition to a spin-polarized Fermi liquid at some magnetic field larger than the pair-breaking field is predicted.Comment: 4 pages, 4 figures, references update

Eikonal Evolution and Gluon Radiation

We give a simple quantum mechanical formulation of the eikonal propagation approximation, which has been heavily used in recent years in problems involving hadronic interactions at high energy. This provides a unified framework for several approaches existing in the literature. We illustrate this scheme by calculating the total, elastic, inelastic and diffractive DIS cross sections, as well as gluon production in high energy hadronic collisions. From the q-qbar-g-component of the DIS cross sections, we straightforwardly derive low x evolution equations for inelastic and diffractive DIS distribution functions. In all calculations, we provide all order 1/N corrections to the results existing in the literature.Comment: 40 pages, LaTeX, 3 eps-figures, typos corrected, to be published in PR

Geometric phase shift in quantum computation using superconducting nanocircuits: nonadiabatic effects

The nonadiabatic geometric quantum computation may be achieved using coupled low-capacitance Josephson juctions. We show that the nonadiabtic effects as well as the adiabatic condition are very important for these systems. Moreover, we find that it may be hard to detect the adiabatic Berry's phase in this kind of superconducting nanocircuits; but the nonadiabatic phase may be measurable with current techniques. Our results may provide useful information for the implementation of geometric quantum computation.Comment: 5 pages; A slightly different version with PRA 66, 04232

Spin and Current Variations in Josephson Junctions

We study the dynamics of a single spin embedded in the tunneling barrier between two superconductors. As a consequence of pair correlations in the superconducting state, the spin displays rich and unusual dynamics. To properly describe the time evolution of the spin we derive the effective Keldysh action for the spin. The superconducting correlations lead to an effective spin action, which is non-local in time, leading to unconventional precession. We further illustrate how the current is modulated by this novel spin dynamics