266 research outputs found
Dynamical Casimir effect entangles artificial atoms
We show that the physics underlying the dynamical Casimir effect may generate
multipartite quantum correlations. To achieve it, we propose a circuit quantum
electrodynamics (cQED) scenario involving superconducting quantum interference
devices (SQUIDs), cavities, and superconducting qubits, also called artificial
atoms. Our results predict the generation of highly entangled states for two
and three superconducting qubits in different geometric configurations with
realistic parameters. This proposal paves the way for a scalable method of
multipartite entanglement generation in cavity networks through dynamical
Casimir physics.Comment: Improved version and references added. Accepted for publication in
Physical Review Letter
Quantum Phase Transitions in Josephson Junction Chains
We investigate the quantum phase transition in a one-dimensional chain of
ultra-small superconducting grains, considering both the self- and junction
capacitances. At zero temperature, the system is transformed into a
two-dimensional system of classical vortices, where the junction capacitance
introduces anisotropy in the interaction between vortices. This leads to the
superconductor-insulator transition of the Berezinskii-Kosterlitz-Thouless
type, as the ratios of the Josephson coupling energy to the charging energies
are varied. It is found that the junction capacitance plays a role similar to
that of dissipation and tends to suppress quantum fluctuations; nevertheless
the insulator region survives even for arbitrarily large values of the junction
capacitance.Comment: REVTeX+5 EPS figures, To appear in PRB Rapid
Scaling Analysis of Magnetic Filed Tuned Phase Transitions in One-Dimensional Josephson Junction Arrays
We have studied experimentally the magnetic field-induced
superconductor-insulator quantum phase transition in one-dimensional arrays of
small Josephson junctions. The zero bias resistance was found to display a
drastic change upon application of a small magnetic field; this result was
analyzed in context of the superfluid-insulator transition in one dimension. A
scaling analysis suggests a power law dependence of the correlation length
instead of an exponential one. The dynamical exponents were determined to
be close to 1, and the correlation length critical exponents were also found to
be about 0.3 and 0.6 in the two groups of measured samples.Comment: 4 pages, 4 figure
Capacitively coupled Josephson-junction chains: straight and slanted coupling
Two chains of ultrasmall Josephson junctions, coupled capacitively with each
other in the two different ways, straight and slanted coupling, are considered.
As the coupling capacitance increases, regardless of the coupling scheme, the
transport of particle-hole pairs in the system is found to drive the
quantum-phase transition at zero temperature, which is a
insulator-to-superfluid transition of the particle-hole pairs and belongs to
the Berezinskii-Kosterlitz-Thouless universal class. The different underlying
transport mechanisms for the two coupling schemes are reflected in the
difference between the transition points.Comment: REVTeX + 7 EPS figures, detailed version of cond-mat/980219
An Experimentally Realizable Weiss Model for Disorder-Free Glassiness
We summarize recent work on a frustrated periodic long-range Josephson array
in a parameter regime where its dynamical behavior is identical to that of the
disordered spherical model. We also discuss the physical requirements
imposed by the theory on the experimental realization of this superconducting
network.Comment: 6 pages, LaTeX, 2 Postscript figure
A ruin model with a resampled environment
This paper considers a Cramér–Lundberg risk setting, where the components of the underlying model change over time. We allow the more general setting of the cumulative claim process being modeled as a spectrally positive Lévy process. We provide an intuitively appealing mechanism to create such parameter uncertainty: at Poisson epochs, we resample the model components from a finite number of d settings. It results in a setup that is particularly suited to describe situations in which the risk reserve dynamics are affected by external processes. We extend the classical Cramér–Lundberg approximation (asymptotically characterizing the all-time ruin probability in a light-tailed setting) to this more general setup. In addition, for the situation that the driving Lévy processes are sums of Brownian motions and compound Poisson processes, we find an explicit uniform bound on the ruin probability. In passing we propose an importance-sampling algorithm facilitating efficient estimation, and prove it has bounded relative error. In a series of numerical experiments we assess the accuracy of the asymptotics and bounds, and illustrate that neglecting the resampling can lead to substantial underestimation of the risk
Shot Noise of Single-Electron Tunneling in 1D Arrays
We have used numerical modeling and a semi-analytical calculation method to
find the low frequency value S_{I}(0) of the spectral density of fluctuations
of current through 1D arrays of small tunnel junctions, using the ``orthodox
theory'' of single-electron tunneling. In all three array types studied, at low
temperature (kT << eV), increasing current induces a crossover from the
Schottky value S_{I}(0)=2e to the ``reduced Schottky value''
S_{I}(0)=2e/N (where N is the array length) at some crossover current I_{c}.
In uniform arrays over a ground plane, I_{c} is proportional to exp(-\lambda
N), where 1/\lambda is the single-electron soliton length. In arrays without a
ground plane, I_{c} decreases slowly with both N and \lambda. Finally, we have
calculated the statistics of I_{c} for ensembles of arrays with random
background charges. The standard deviation of I_{c} from the ensemble average
is quite large, typically between 0.5 and 0.7 of , while the
dependence of on N or \lambda is so weak that it is hidden within the
random fluctuations of the crossover current.Comment: RevTex. 21 pages of text, 10 postscript figure
Escape from a zero current state in a one dimensional array of Josephson junctions
A long one dimensional array of small Josephson junctions exhibits Coulomb
blockade of Cooper pair tunneling. This zero current state exists up to a
switching voltage, Vsw, where there is a sudden onset of current. In this paper
we present histograms showing how Vsw changes with temperature for a long array
and calculations of the corresponding escape rates. Our analysis of the problem
is based on the existence of a voltage dependent energy barrier and we do not
make any assumptions about its shape. The data divides up into two temperature
regimes, the higher of which can be explained with Kramers thermal escape
model. At low temperatures the escape becomes independent of temperature.Comment: 4 pages 5 figure
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