Charge Transport in Voltage-Biased Superconducting Single-Electron Transistors

Charge is transported through superconducting SSS single-electron transistors at finite bias voltages by a combination of coherent Cooper-pair tunneling and quasiparticle tunneling. At low transport voltages the effect of an ``odd'' quasiparticle in the island leads to a $2e$-periodic dependence of the current on the gate charge. We evaluate the $I-V$ characteristic in the framework of a model which accounts for these effects as well as for the influence of the electromagnetic environment. The good agreement between our model calculation and experimental results demonstrates the importance of coherent Cooper-pair tunneling and parity effects.Comment: RevTeX, 12 pages, 4 figure

The Opioid Antagonist Naltrexone Improves Murine Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a condition of the intestine with significant morbidity. Although hereditary, environmental, immunologic, and bacterial factors have been implicated, the etiology of IBD remains unknown. Since opioid peptides modulate inflammatory cytokine production and opioid antagonists promote tissue growth and repair, we hypothesized the opioid antagonist naltrexone could reduce inflammation of the bowel. Using a chemically-induced mouse model of IBD, C57BL/6J mice received either untreated drinking water or water containing 2% dextran sulfate sodium (DSS) in two parallel regimens modeling moderate and severe colitis. After colitis was established, animals in the moderate colitis study were administered either saline (control) or naltrexone (NTX; 8 or 400 μ g/kg) daily, while those in the severe colitis study received 0.1 or 10 mg/kg NTX. DSS-treated animals had significant weight loss (p = 0.006) and higher disease activity index (DAI) scores (p \u3c 0.001) compared to water controls. However, NTX treatment of mice with moderate colitis resulted in less weight loss, lower DAI scores, and less histologic evidence of inflammation compared to controls. Significantly, elevated levels of colonic RNA for pro-inflammatory cytokines interleukin (IL)-6 and IL-12 were also decreased toward normal with NTX. Similar to patients with severe and unresponsive disease, animals in the severe colitis study did not significantly respond to treatment. Thus, NTX therapy reverses physical symptoms, histologic evidence, and molecular markers of inflammation in moderate colitis. The mechanism by which NTX acts to reverse colitis is related in part to the decreased expression of pro-inflammatory cytokines

Cotunneling Transport and Quantum Phase Transitions in Coupled Josephson-Junction Chains with Charge Frustration

We investigate the quantum phase transitions in two capacitively coupled chains of ultra-small Josephson-junctions, with emphasis on the external charge effects. The particle-hole symmetry of the system is broken by the gate voltage applied to each superconducting island, and the resulting induced charge introduces frustration to the system. Near the maximal-frustration line, where the system is transformed into a spin-1/2 Heisenberg antiferromagnetic chain, cotunneling of the particles along the two chains is shown to play a major role in the transport and to drive a quantum phase transition out of the charge-density wave insulator, as the Josephson-coupling energy is increased. We also argue briefly that slightly off the symmetry line, the universality class of the transition remains the same as that right on the line, still being driven by the particle-hole pairs.Comment: Final version accepted to Phys. Rev. Lett. (Longer version is available from http://ctp.snu.ac.kr/~choims/

Charge Frustration Effects in Capacitively Coupled Two-Dimensional Josephson-Junction Arrays

We investigate the quantum phase transitions in two capacitively coupled two-dimensional Josephson-junction arrays with charge frustration. The system is mapped onto the S=1 and $S=1/2$ anisotropic Heisenberg antiferromagnets near the particle-hole symmetry line and near the maximal-frustration line, respectively, which are in turn argued to be effectively described by a single quantum phase model. Based on the resulting model, it is suggested that near the maximal frustration line the system may undergo a quantum phase transition from the charge-density wave to the super-solid phase, which displays both diagonal and off- diagonal long-range order.Comment: 6 pages, 6 figures, to appear in Phys. Rev.

Fidelity and leakage of Josephson qubits

The unit of quantum information is the qubit, a vector in a two-dimensional Hilbert space. On the other hand, quantum hardware often operates in two-dimensional subspaces of vector spaces of higher dimensionality. The presence of higher quantum states may affect the accuracy of quantum information processing. In this Letter we show how to cope with {\em quantum leakage} in devices based on small Josephson junctions. While the presence of higher charge states of the junction reduces the fidelity during gate operations we demonstrate that errors can be minimized by appropriately designing and operating the gates.Comment: 9 pages, Revtex, 2 eps figure

Current drag in capacitevly coupled Luttinger constrictions

We study the current drag in the system of two electrostatically coupled finite 1D electron channels. We present the perturbation theory results along with the results for two non-perturbative regimes. It is shown that the drag may become absolute, that is, the currents in the channels are equal in a finite window of the bias voltages.Comment: 4 pages RevTeX, 3 postscript figure

Non-equlibrium effects in transport through quantum dots

The role of non-equilibrium effects in the conductance through quantum dots is investigated. Associated with single-electron tunneling are shake-up processes and the formation of excitonic-like resonances. They change qualitatively the low temperature properties of the system. We analyze by quantum Monte Carlo methods the renormalization of the effective capacitance and the gate-voltage dependent conductance. Experimental relevance is discussed.Comment: 10 pages, 8 postscript figure

Investigation of \u3csup\u3e186\u3c/sup\u3eRe via radiative thermal-neutron capture on \u3csup\u3e185\u3c/sup\u3eRe

Partial -ray production cross sections and the total radiative thermal-neutron capture cross section for the 185Re(n,)186Re reaction were measured using the Prompt Gamma Activation Analysis facility at the Budapest Research Reactor with an enriched 185Re target. The 186Re cross sections were standardized using well-known 35Cl(n,)36Cl cross sections from irradiation of a stoichiometric natReCl3 target. The resulting cross sections for transitions feeding the 186Re ground state from low-lying levels below a cutoff energy of Ec=746keV were combined with a modeled probability of ground-state feeding from levels above Ec to arrive at a total cross section of σ0=111(6)b for radiative thermal-neutron capture on 185Re. A comparison of modeled discrete-level populations with measured transition intensities led to proposed revisions for seven tentative spin-parity assignments in the adopted level scheme for 186Re. Additionally, 102 primary rays were measured, including 50 previously unknown. A neutron-separation energy of Sn=6179.59(5)keV was determined from a global least-squares fit of the measured -ray energies to the known 186Re decay scheme. The total capture cross section and separation energy results are comparable to earlier measurements of these values

Geometric Quantum Computation on Solid-State Qubits

An adiabatic cyclic evolution of control parameters of a quantum system ends up with a holonomic operation on the system, determined entirely by the geometry in the parameter space. The operation is given either by a simple phase factor (a Berry phase) or a non-Abelian unitary operator depending on the degeneracy of the eigenspace of the Hamiltonian. Geometric quantum computation is a scheme to use such holonomic operations rather than the conventional dynamic operations to manipulate quantum states for quantum information processing. Here we propose a geometric quantum computation scheme which can be realized with current technology on nanoscale Josephson-junction networks, known as a promising candidate for solid-state quantum computer.Comment: 6 figures; to appear in J. Phys.: Condens. Mat