69 research outputs found
Distinguishing quantum from classical oscillations in a driven phase qubit
Rabi oscillations are coherent transitions in a quantum two-level system
under the influence of a resonant perturbation, with a much lower frequency
dependent on the perturbation amplitude. These serve as one of the signatures
of quantum coherent evolution in mesoscopic systems. It was shown recently [N.
Gronbech-Jensen and M. Cirillo, Phys. Rev. Lett. 95, 067001 (2005)] that in
phase qubits (current-biased Josephson junctions) this effect can be mimicked
by classical oscillations arising due to the anharmonicity of the effective
potential. Nevertheless, we find qualitative differences between the classical
and quantum effect. First, while the quantum Rabi oscillations can be produced
by the subharmonics of the resonant frequency (multiphoton processes), the
classical effect also exists when the system is excited at the overtones.
Second, the shape of the resonance is, in the classical case,
characteristically asymmetric; while quantum resonances are described by
symmetric Lorentzians. Third, the anharmonicity of the potential results in the
negative shift of the resonant frequency in the classical case, in contrast to
the positive Bloch-Siegert shift in the quantum case. We show that in the
relevant range of parameters these features allow to confidently distinguish
the bona fide Rabi oscillations from their classical Doppelganger.Comment: 8 pages, 4 figures; v2: minor corrections, Fig.1 added, introduction
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Giving electrons a ride: nanomechanical electron shuttles
Nanomechanical shuttles transferring small groups of electrons or even
individual electrons from one electrode to another offer a novel approach to
the problem of controlled charge transport. Here, we report the fabrication of
shuttle-junctions consisting of a 20 nm diameter gold nanoparticle embedded
within the gap between two gold electrodes. The nanoparticle is attached to the
electrodes through a monolayer of flexible organic molecules which play the
role of springs so that when a sufficient voltage bias is applied, then
nanoparticle starts to oscillate transferring electrons from one electrode to
the other. Current-voltage characteristics for the fabricated devices have been
measured and compared with the results of our computer simulations.Comment: 11 pages, 4 figure
Beer classification based on the array of solid-contact Potentiometric sensors with thiacalixarene receptors
Potentiometric sensors based on carbon electrodes made by screen-printing and glassy carbon electrodes covered with electropolymerized polyaniline and thiacalix[4]arene receptors have been developed for discrimination of various beer brands using three sensors. The prediction was 100% true according to principal component analysis and linear discriminant analysis. © 2014 Springer Science+Business Media, Inc
Terahertz Josephson plasma waves in layered superconductors: spectrum, generation, nonlinear, and quantum phenomena
The recent growing interest in terahertz (THz) and sub-THz science and
technology is due to its many important applications in physics, astronomy,
chemistry, biology, and medicine. We review the problem of linear and
non-linear THz and sub-THz Josephson plasma waves in layered superconductors
and their excitations produced by moving Josephson vortices. We start by
discussing the coupled sine-Gordon equations for the gauge-invariant phase
difference of the order parameter in the junctions, taking into account the
effect of breaking the charge neutrality, and deriving the spectrum of
Josephson plasma waves. We also review surface and waveguide Josephson plasma
waves. We review the propagation of weakly nonlinear Josephson plasma waves
below the plasma frequency, which is very unusual for plasma-like excitations.
In close analogy to nonlinear optics, these waves exhibit numerous remarkable
features, including a self-focusing effect, and the pumping of weaker waves by
a stronger one. We also present quantum effects in layered superconductors,
specifically, the problem of quantum tunnelling of fluxons through stacks of
Josephson junctions. We discuss the Cherenkov and transition radiations of the
Josephson plasma waves produced by moving Josephson vortices. We also discuss
the problem of coherent radiation (superradiance) of the THz waves by exciting
uniform Josephson oscillations. The effects reviewed here could be potentially
useful for sub-THz and THz emitters, filters, and detectors
The role of tryptophanyl residues in the function of Aspergillus niger glucoamylase G1 and G2
Beer classification based on the array of solid-contact potentiometric sensors with thiacalixarene receptors
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