Production of non-local quartets and phase-sensitive entanglement in a superconducting beam splitter

Three BCS superconductors S_a, S_b, and S and two short normal regions N_a and N_b in a three-terminal S_aN_aSN_bS_b set-up provide a source of non-local quartets spatially separated as two correlated pairs in S_a and S_b, if the distance between the interfaces N_aS and SN_b is comparable to the coherence length in S. Low-temperature dc-transport of non-local quartets from S to S_a and S_b can occur in equilibrium, and also if S_a and S_b are biased at opposite voltages. At higher temperatures, thermal excitations result in correlated current fluctuations which depend on the superconducting phases phi_a and phi_b in S_a and S_b. Phase-sensitive entanglement is obtained at zero temperature if N_a and N_b are replaced by discrete levels.Comment: 4 pages, 2 figures; technical details attached in ancillary file http://arxiv.org/src/1102.2355v4/anc/EPAPS_Freyn_2011.pdf; higher versions: minor corrections, cleanup and corrected reference

Electrical stress effect on Josephson tunneling through ultrathin AlOx barrier in Nb/Al/AlOx/Nb junctions

The effect of dc electrical stress and breakdown on Josephson and quasiparticle tunneling in Nb/Al/AlOx/Nb junctions with ultrathin AlOx barriers typical for applications in superconductor digital electronics has been investigated. The junctions' conductance at room temperature and current-voltage (I-V) characteristics at 4.2 K have been measured after the consecutive stressing of the tunnel barrier at room temperature. Electrical stress was applied using current ramps with increasing amplitude ranging from 0 to ~1000 Ic corresponding to voltages across the barrier up to 0.65 V where Ic is the Josephson critical current. A very soft breakdown has been observed with polarity-dependent breakdown current (voltage). A dramatic increase in subgap conductance of the junctions, the appearance of subharmonic current steps, and gradual increase in both the critical and the excess currents as well as a decrease in the normal-state resistance have been observed. The observed changes in superconducting tunneling suggest a model in which a progressively increasing number of defects and associated additional conduction channels (superconducting quantum point contacts (SQPCs)) are induced by electric field in the tunnel barrier. By comparing the I-V characteristics of these conduction channels with the nonstationary theory of current transport in SQPCs based on multiple Andreev reflections by Averin and Bardas, the typical transparency D of the induced SQPCs was estimated as D ~ 0.7. The number of induced SQPCs was found to grow with voltage across the barrier as sinh(V/V_0) with V_0 = 0.045 V, in good agreement with the proposed model of defect formation by ion electromigration. The observed polarity dependence of the breakdown current (voltage) is also consistent with the model.Comment: 11 pages, 10 figure

Interactions and Interference in Quantum Dots: Kinks in Coulomb Blockade Peak Positions

We investigate the spin of the ground state of a geometrically confined many-electron system. For atoms, shell structure simplifies this problem-- the spin is prescribed by the well-known Hund's rule. In contrast, quantum dots provide a controllable setting for studying the interplay of quantum interference and electron-electron interactions in general cases. In a generic confining potential, the shell-structure argument suggests a singlet ground state for an even number of electrons. The interaction among the electrons produces, however, accidental occurrences of spin-triplet ground states, even for weak interaction, a limit which we analyze explicitly. Variaton of an external parameter causes sudden switching between these states and hence a kink in the conductance. Experimental study of these kinks would yield the exchange energy for the ``chaotic electron gas''.Comment: 4 pages, 2 ps figs included using epsf.sty. Revision: added important reference and consequent text changes, other small correction

Exudative pericarditis with tamponade after COVID-19. Case report

A description of a COVID-19 patient with the development of exudative pericarditis complicated by cardiac tamponade is provid. A peculiarity of this case is the presence of an underlying disease in the patient (chronic lymphocytic leukemia), which was in remission for 1.5 years after chemotherapy. Another feature of the patient was the relatively small area of lung damage and the hemorrhagic nature of the pericardial effusion, which persisted for a long time. The insignificant activity of inflammatory markers was noteworthy. Possible mechanisms of development and features of the course of exudative pericarditis in the described patient, issues of diagnosis and treatment of this category of patients are discusse