682 research outputs found
Controlling Josephson transport by manipulation of Andreev levels in ballistic mesoscopic junctions
We discuss how to control dc Josephson current by influencing the structure
and nonequilibrium population of Andreev levels via external electrostatic
gates, external current injection and electromagnetic radiation. In particular
we will consider the "giant" Josephson current in "long" SIS tunnel junctions
and the regular and anomalous nonequilibrium Josephson currents in three
terminal SNS junctions. We will briefly discuss applications to the Josephson
field effect transistor (JOFET) and to the newly invented Josephson
interference transistor (JOINT).Comment: 10 pages, 3 figures; contribution to a special volume of
Superlattices and Microstructures journal (ed. P.F. Bagwell
Toward bio-inspired information processing with networks of nano-scale switching elements
Unconventional computing explores multi-scale platforms connecting
molecular-scale devices into networks for the development of scalable
neuromorphic architectures, often based on new materials and components with
new functionalities. We review some work investigating the functionalities of
locally connected networks of different types of switching elements as
computational substrates. In particular, we discuss reservoir computing with
networks of nonlinear nanoscale components. In usual neuromorphic paradigms,
the network synaptic weights are adjusted as a result of a training/learning
process. In reservoir computing, the non-linear network acts as a dynamical
system mixing and spreading the input signals over a large state space, and
only a readout layer is trained. We illustrate the most important concepts with
a few examples, featuring memristor networks with time-dependent and history
dependent resistances
Superconducting Quantum Circuits, Qubits and Computing
This paper gives an introduction to the physics and principles of operation
of quantized superconducting electrical circuits for quantum information
processing.Comment: 59 pages 68 figures. Prepared for Handbook of Theoretical and
Computational Nanotechnolog
Selective coupling of superconducting qubits via tunable stripline cavity
We theoretically investigate selective coupling of superconducting charge
qubits mediated by a superconducting stripline cavity with a tunable resonance
frequency. The frequency control is provided by a flux biased dc-SQUID attached
to the cavity. Selective entanglement of the qubit states is achieved by
sweeping the cavity frequency through the qubit-cavity resonances. The circuit
is scalable, and allows to keep the qubits at their optimal points with respect
to decoherence during the whole operation. We derive an effective quantum
Hamiltonian for the basic, two-qubit-cavity system, and analyze appropriate
circuit parameters. We present a protocol for performing Bell inequality
measurements, and discuss a composite pulse sequence generating a universal
control-phase gate
Scattering theory of superconductive tunneling in quantum junctions
We present a consistent theory of superconductive tunneling in single-mode
junctions within a scattering formulation of Bogoliubov-de Gennes quantum
mechanics. Both dc Josephson effect and dc quasiparticle transport in voltage
biased junctions are considered. Elastic quasiparticle scattering by the
junction determines equilibrium Josephson current. We discuss the origin of
Andreev bound states in tunnel junctions and their role in equilibrium
Josephson transport. In contrast, quasiparticle tunneling in voltage biased
junctions is determined by inelastic scattering. We derive a general expression
for inelastic scattering amplitudes and calculate the quasiparticle current at
all voltages with emphasis on a discussion of the properties of subgap tunnel
current and the nature of subharmonic gap structure.Comment: 47 pages, 9 figures, [preprint,eqsecnum,aps]{revtex
Interference effects in phtalocyanine controlled by H-H tautomerization: a potential two-terminal unimolecular electronic switch
We investigate the electrical transport properties of two hydrogen tautomer
configurations of phthalocyanine (H2Pc) connected to cumulene and gold leads.
Hydrogen tautomerization affects the electronic state of H2Pc by switching the
character of molecular orbitals with the same symmetry close to the Fermi
level. The near degeneracy between the HOMO and HOMO-1 leads to pronounced
interference effects, causing a large change in current for the two tautomer
configuratons, especially in the low-bias regime. Two types of planar junctions
are considered: cumulene-H2Pc-cumulene and gold-H2Pc-gold. Both demonstrate
prominent difference in molecular conductance between ON and OFF states. In
addition, junctions with gold leads show pronounced negative differential
resistance (NDR) at high bias voltage, as well as weak NDR at intermediate
bias.Comment: 10 pages, 7 figures, accepted for publication in Physical Review
Readout methods and devices for Josephson-junction-based solid-state qubits
We discuss the current situation concerning measurement and readout of
Josephson-junction based qubits. In particular we focus attention of dispersive
low-dissipation techniques involving reflection of radiation from an oscillator
circuit coupled to a qubit, allowing single-shot determination of the state of
the qubit. In particular we develop a formalism describing a charge qubit read
out by measuring its effective (quantum) capacitance. To exemplify, we also
give explicit formulas for the readout time.Comment: 20 pages, 7 figures. To be published in J. Phys.: Condensed Matter,
18 (2006) Special issue: Quantum computin
Coherent multiple Andreev reflections and current resonances in SNS junctions
We study coherent multiple Andreev reflections in quantum SNS junctions of
finite length and arbitrary transparency. The presence of superconducting bound
states in these junctions gives rise to great enhancement of the subgap
current. The effect is most pronounced in low-transparency junctions, ,
and in the interval of applied voltage , where the
amplitude of the current structures is proportional to the first power of the
junction transparency . The resonant current structures consist of steps and
oscillations of the two-particle current and also of multiparticle resonance
peaks. The positions of the two-particle current structures have pronounced
temperature dependence which scales with , while the positions of
the multiparticle resonances have weak temperature dependence, being mostly
determined by the junction geometry. Despite the large resonant two-particle
current, the excess current at large voltage is small and proportional to
. Pacs: 74.50.+r, 74.80.Fp, 74.20.Fg, 73.23.AdComment: 23 pages, 16 figure
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