Circuit theory of crossed Andreev reflection

We consider transport in a three terminal device attached to one superconducting and two normal metal terminals, using the circuit theory of mesoscopic superconductivity. We compute the nonlocal conductance of the current out of the first normal metal terminal in response to a bias voltage between the second normal metal terminal and the superconducting terminal. The nonlocal conductance is given by competing contributions from crossed Andreev reflection and electron cotunneling, and we determine the contribution from each process. The nonlocal conductance vanishes when there is no resistance between the superconducting terminal and the device, in agreement with previous theoretical work. Electron cotunneling dominates when there is a finite resistance between the device and the superconducting reservoir. Decoherence is taken into account, and the characteristic timescale is the particle dwell time. This gives rise to an effective Thouless energy. Both the conductance due to crossed Andreev reflection and electron cotunneling depend strongly on the Thouless energy. We suggest to experimentally determine independently the conductance due to crossed Andreev reflection and electron cotunneling in measurement of both energy and charge flow into one normal metal terminal in response to a bias voltage between the other normal metal terminal and the superconductor.Comment: v2: Published version with minor changes, 12 pages and 9 figure

Controlled splitting of an atomic wave packet

We propose a simple scheme capable of adiabatically splitting an atomic wave packet using two independent translating traps. Implemented with optical dipole traps, our scheme allows a high degree of flexibility for atom interferometry arrangements and highlights its potential as an efficient and high fidelity atom optical beam splitter.Comment: 4 pages, 4 figures. Accepted by Phys. Rev. Let

Step velocity tuning of SrRuO3 step flow growth on SrTiO3

Taking advantage of vicinal (001) SrTiO3 substrates with different mean terrace widths, the heteroepitaxial growth of SrRuO3 in the step flow mode has been mapped as a function of mean step velocity. Transition between stable and unstable step flow is shown to occur at a well-defined critical step velocity, with a step bunching instability observed below this threshold. The ability to pass from unstable to stable step flow during growth upon increasing the mean step velocity is demonstrated. This result is discussed in terms of a stress-based driving force for step bunching in competition with an effective step-up adatom current.Comment: 4 pages, 3 figure

Measuring the distribution of current fluctuations through a Josephson junction with very short current pulses

We propose to probe the distribution of current fluctuations by means of the escape probability histogram of a Josephson junction (JJ), obtained using very short bias current pulses in the adiabatic regime, where the low-frequency component of the current fluctuations plays a crucial role. We analyze the effect of the third cumulant on the histogram in the small skewness limit, and address two concrete examples assuming realistic parameters for the JJ. In the first one we study the effects due to fluctuations produced by a tunnel junction, finding that the signature of higher cumulants can be detected by taking the derivative of the escape probability with respect to current. In such a realistic situation, though, the determination of the whole distribution of current fluctuations requires an amplification of the cumulants. As a second example we consider magnetic flux fluctuations acting on a SQUID produced by a random telegraph source of noise.Comment: 6 pages, 6 figures; final versio

Specular reflection of matter waves from a rough mirror

We have made a high resolution study of the specularity of the atomic reflection from an evanescent wave mirror using velocity selective Raman transitions. We have observed a double structure in the velocity distribution after reflection: a peak consistent with specular reflection and a diffuse reflection pedestal, whose contribution decreases rapidly with increasing detuning. The diffuse reflection is due to two distinct effects: spontaneous emission in the evanescent wave and a roughness in the evanescent wave potential whose amplitude is smaller than the de Broglie wavelength of the reflected atoms

Spin squeezing, entanglement and quantum metrology with Bose-Einstein condensates

Squeezed states, a special kind of entangled states, are known as a useful resource for quantum metrology. In interferometric sensors they allow to overcome the "classical" projection noise limit stemming from the independent nature of the individual photons or atoms within the interferometer. Motivated by the potential impact on metrology as wells as by fundamental questions in the context of entanglement, a lot of theoretical and experimental effort has been made to study squeezed states. The first squeezed states useful for quantum enhanced metrology have been proposed and generated in quantum optics, where the squeezed variables are the coherences of the light field. In this tutorial we focus on spin squeezing in atomic systems. We give an introduction to its concepts and discuss its generation in Bose-Einstein condensates. We discuss in detail the experimental requirements necessary for the generation and direct detection of coherent spin squeezing. Two exemplary experiments demonstrating adiabatically prepared spin squeezing based on motional degrees of freedom and diabatically realized spin squeezing based on internal hyperfine degrees of freedom are discussed.Comment: Phd tutorial, 23 pages, 17 figure

A malignant hyperthermia–inducing mutation in RYR1 (R163C): consequent alterations in the functional properties of DHPR channels

Bidirectional communication between the 1,4-dihydropyridine receptor (DHPR) in the plasma membrane and the type 1 ryanodine receptor (RYR1) in the sarcoplasmic reticulum (SR) is responsible for both skeletal-type excitation–contraction coupling (voltage-gated Ca2+ release from the SR) and increased amplitude of L-type Ca2+ current via the DHPR. Because the DHPR and RYR1 are functionally coupled, mutations in RYR1 that are linked to malignant hyperthermia (MH) may affect DHPR activity. For this reason, we investigated whether cultured myotubes originating from mice carrying an MH-linked mutation in RYR1 (R163C) had altered voltage-gated Ca2+ release from the SR, membrane-bound charge movement, and/or L-type Ca2+ current. In myotubes homozygous (Hom) for the R163C mutation, voltage-gated Ca2+ release from the SR was substantially reduced and shifted (∼10 mV) to more hyperpolarizing potentials compared with wild-type (WT) myotubes. Intramembrane charge movements of both Hom and heterozygous (Het) myotubes displayed hyperpolarizing shifts similar to that observed in voltage-gated SR Ca2+ release. The current–voltage relationships for L-type currents in both Hom and Het myotubes were also shifted to more hyperpolarizing potentials (∼7 and 5 mV, respectively). Compared with WT myotubes, Het and Hom myotubes both displayed a greater sensitivity to the L-type channel agonist ±Bay K 8644 (10 µM). In general, L-type currents in WT, Het, and Hom myotubes inactivated modestly after 30-s prepulses to −50, −10, 0, 10, 20, and 30 mV. However, L-type currents in Hom myotubes displayed a hyperpolarizing shift in inactivation relative to L-type currents in either WT or Het myotubes. Our present results indicate that mutations in RYR1 can alter DHPR activity and raise the possibility that this altered DHPR function may contribute to MH episodes

Is neuroblastoma screening evaluation needed and feasible?

Despite the five million children who have been screened for neuroblastoma in Japan through detection of catecholamine metabolites, it is still uncertain whether screening for this disease is beneficial. The Japanese study has clearly indicated that screening at 6 months or earlier leads to heavy overdiagnosis. It is shown in this paper that screening at a later age may give the same reduction in mortality with possibly less overdiagnosis. However, it is estimated that, even with two screens at 12 and 18 months, the reduction in mortality would not greatly exceed 25%, under realistic hypotheses on the length of the preclinical phase of the disease. The evaluation of the efficacy of this screening strategy would need the recruitment of half a million children per year over 5-7 years and the follow-up of an equal number of controls. Such a trial would improve our knowledge of the natural history of the disease and might help to answer some questions raised recently regarding its biological heterogeneity

High kinetic inductance microwave resonators made by He-Beam assisted deposition of tungsten nanowires

We evaluate the performance of hybrid microwave resonators made by combining sputtered Nb thin films with Tungsten nanowires grown with a He-beam induced deposition technique. Depending on growth conditions, the nanowires have a typical width w [35 - 75] nm and thickness t [5 - 40] nm. We observe a high normal state resistance R [65 - 150] Ω / which together with a critical temperature T c [4 - 6] K ensures a high kinetic inductance making the resonator strongly nonlinear. Both lumped and coplanar waveguide resonators were fabricated and measured at low temperature exhibiting internal quality factors up to 3990 at 4.5 GHz in the few photon regime. Analyzing the wire length, temperature, and microwave power dependence, we extracted a kinetic inductance for the W nanowire of L K 15 pH / which is 250 times higher than the geometrical inductance, and a Kerr non-linearity as high as K W, He / 2 π = 200 ± 120 Hz / photon at 4.5 GHz. The nanowires made with the helium focused ion beam are thus versatile objects to engineer compact, high impedance, superconducting environments with a mask and resist free direct write process

Effective spin model for interband transport in a Wannier-Stark lattice system

We show that the interband dynamics in a tilted two-band Bose-Hubbard model can be reduced to an analytically accessible spin model in the case of resonant interband oscillations. This allows us to predict the revival time of these oscillations which decay and revive due to inter-particle interactions. The presented mapping onto the spin model and the so achieved reduction of complexity has interesting perspectives for future studies of many-body systems.Comment: 7 pages, 4 figure