21 research outputs found
600 GHz resonant mode in a parallel array of Josephson tunnel junctions connected by superconducting microstrip lines
Self-induced magnetic field effects caused by edge currents in parallel array of Josephson junctions
Tunneling without tunneling: wavefunction reduction in a mesoscopic qubit
The transformation cycle and associated inequality are suggested for the
basic demonstration of the wavefunction reduction in a mesoscopic qubit in
measurements with quantum-limited detectors. Violation of the inequality would
show directly that the qubit state changes in a way dictated by the
probabilistic nature of the wavefunction and inconsistent with the dynamics of
the Schr\"{o}dinger equation: the qubit tunnels through an infinitely large
barrier. Estimates show that the transformation cycle is within the reach of
current experiments with superconducting qubits.Comment: 5 pages, 2 figure
600 GHz resonant mode in a parallel array of Josephson tunnel junctions connected by superconducting microstrip lines
Resonant-Cavity-Induced Phase Locking and Voltage Steps in a Josephson Array
We describe a simple dynamical model for an underdamped Josephson junction
array coupled to a resonant cavity. From numerical solutions of the model in
one dimension, we find that (i) current-voltage characteristics of the array
have self-induced resonant steps (SIRS), (ii) at fixed disorder and coupling
strength, the array locks into a coherent, periodic state above a critical
number of active Josephson junctions, and (iii) when active junctions are
synchronized on an SIRS, the energy emitted into the resonant cavity is
quadratic with . All three features are in agreement with a recent
experiment [Barbara {\it et al}, Phys. Rev. Lett. {\bf 82}, 1963 (1999)]}.Comment: 4 pages, 3 eps figures included. Submitted to PRB Rapid Com
Dynamics of a Josephson Array in a Resonant Cavity
We derive dynamical equations for a Josephson array coupled to a resonant
cavity by applying the Heisenberg equations of motion to a model Hamiltonian
described by us earlier [Phys. Rev. B {\bf 63}, 144522 (2001); Phys. Rev. B
{\bf 64}, 179902 (E)]. By means of a canonical transformation, we also show
that, in the absence of an applied current and dissipation, our model reduces
to one described by Shnirman {\it et al} [Phys. Rev. Lett. {\bf 79}, 2371
(1997)] for coupled qubits, and that it corresponds to a capacitive coupling
between the array and the cavity mode. From extensive numerical solutions of
the model in one dimension, we find that the array locks into a coherent,
periodic state above a critical number of active junctions, that the
current-voltage characteristics of the array have self-induced resonant steps
(SIRS's), that when active junctions are synchronized on a SIRS, the
energy emitted into the resonant cavity is quadratic in , and that when a
fixed number of junctions is biased on a SIRS, the energy is linear in the
input power. All these results are in agreement with recent experiments. By
choosing the initial conditions carefully, we can drive the array into any of a
variety of different integer SIRS's. We tentatively identify terms in the
equations of motion which give rise to both the SIRS's and the coherence
threshold. We also find higher-order integer SIRS's and fractional SIRS's in
some simulations. We conclude that a resonant cavity can produce threshold
behavior and SIRS's even in a one-dimensional array with appropriate
experimental parameters, and that the experimental data, including the coherent
emission, can be understood from classical equations of motion.Comment: 15 pages, 10 eps figures, submitted to Phys. Rev.
Mobile kinks and half-integer zero-field-like steps in highly discrete alternating Josephson junction arrays
The dynamics of a one-dimensional, highly discrete, linear array of
alternating and Josephson junctions is studied numerically, under
constant bias current at zero magnetic field. The calculated current - voltage
characteristics exhibit half-integer and integer zero-field-like steps for even
and odd total number of junctions, respectively. Inspection of the
instantaneous phases reveals that, in the former case, single kink
excitations (discrete semi-fluxons) are supported, whose propagation in the
array gives rise to the step, while in the latter case, a pair of
kink -- antikink appears, whose propagation gives rise to the
step. When additional kinks are inserted in the array, they are
subjected to fractionalization, transforming themselves into two closely spaced
kinks. As they propagate in the array along with the single kink or
the kink - antikink pair, they give rise to higher half-integer or
integer zero-field-like steps, respectively.Comment: 7 pages, 8 figures, submitted to Supercond. Sci. Techno