7,158 research outputs found
Impact of the transport supercurrent on the Josephson effect
We study the weak link between current-carrying superconductors, both
conventional and d-wave. The state of the system is controlled by two
parameters: the order parameter phase difference and the superfluid
velocity , which parameterizes the parallel to the boundary transport
supercurrent which is injected externally. The low-temperature current-phase
relations are derived. We consider two models of weak links: a constriction
between two conventional superconductors and a plane boundary between two
differently orientated d-wave superconductors. We show that for some relation
between and quasiparticles create the current along the
boundary which flows in the direction opposite to the transport supercurrent.Comment: 5 pages, 3 figures; submitted for publication in Proceedings of
MS+S2004 symposium (without Sec.V and the last part of Sec.III
Resonant effects in the strongly driven phase-biased Cooper-pair box
We study the time-averaged upper level occupation probability in a strongly
driven two level system, particularly its dependence on the driving amplitude,
frequency and the energy level separation. In contrast to the case of weak
driving, when the positions of the resonances almost do not depend on the
driving amplitude, in the case of the strong diving their positions are
strongly amplitude-dependent. We study these resonances in the concrete system
-- the strongly driven phase-biased Cooper-pair box, which is considered to be
weakly coupled to the tank circuit
Josephson and spontaneous currents at the interface between two d-wave superconductors with transport current in the banks
A stationary Josephson effect in the ballistic contact of two d-wave
superconductors with different axes orientation and with tangential transport
current in the banks is considered theoretically. We study the influence of the
transport current on the current-phase dependence for the Josephson and
tangential currents at the interface. It is demonstrated that the spontaneous
surface current at the interface depends on the transport current in the banks
due to the interference of the angle-dependent current-carrying condensate wave
functions of the two superconductors.Comment: to be published in Fiz. Nizk. Temp. (Sov. J. Low Temp. Phys.),
Vol.30, No.3 (2004
Conductance characteristics of current-carrying d-wave weak links
The local quasiparticle density of states in the current-carrying d-wave
superconducting structures was studied theoretically. The density of states can
be accessed through the conductance of the scanning tunnelling microscope. Two
particular situations were considered: the current state of the homogeneous
film and the weak link between two current-carrying d-wave superconductors.Comment: 4 pages, 3 figures; to appear in Low. Temp. Phy
Resonance at the Rabi frequency in a superconducting flux qubit
We analyze a system composed of a superconducting flux qubit coupled to a
transmission-line resonator driven by two signals with frequencies close to the
resonator's harmonics. The first strong signal is used for exciting the system
to a high energetic state while a second weak signal is applied for probing
effective eigenstates of the system. In the framework of doubly dressed states
we showed the possibility of amplification and attenuation of the probe signal
by direct transitions at the Rabi frequency. We present a brief review of
theoretical and experimental works where a direct resonance at Rabi frequency
have been investigated in superconducting flux qubits. The interaction of the
qubit with photons of two harmonics has prospects to be used as a quantum
amplifier (microwave laser) or an attenuator.Comment: This paper is the extended version of the talk given by one of the
authors at the Conference On Nuclei And Mesoscopic Physics, 5-9 May 2014,
Michigan State University, East Lansing, US
Inverse Landau-Zener-Stuckelberg problem for qubit-resonator systems
We consider theoretically a superconducting qubit - nanomechanical resonator
(NR) system, which was realized by LaHaye et al. [Nature 459, 960 (2009)].
First, we study the problem where the state of the strongly driven qubit is
probed through the frequency shift of the low-frequency NR. In the case where
the coupling is capacitive, the measured quantity can be related to the
so-called quantum capacitance. Our theoretical results agree with the
experimentally observed result that, under resonant driving, the frequency
shift repeatedly changes sign. We then formulate and solve the inverse
Landau-Zener-Stuckelberg problem, where we assume the driven qubit's state to
be known (i.e. measured by some other device) and aim to find the parameters of
the qubit's Hamiltonian. In particular, for our system the qubit's bias is
defined by the NR's displacement. This may provide a tool for monitoring of the
NR's position.Comment: 10 pages, 7 figure
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