975 research outputs found
Density domains of a photo-excited electron gas on liquid helium
The Coulombic effect on the stability range of the photo-excited electron gas
on liquid helium is shown to favor formation of domains of different densities.
Domains appear to eliminate or greatly reduce regions with negative
conductivity. An analysis of the density domain structure allows explaining
remarkable observations reported recently for the photo-excited electron gas.Comment: 5 pages, 5 figure
Multiphoton antiresonance
We show that nonlinear response of a quantum oscillator displays antiresonant
dips and resonant peaks with varying frequency of the driving field. The effect
is a consequence of special symmetry and is related to resonant multiphoton
mixing of several pairs of oscillator states at a time. We discuss the
possibility to observe the antiresonance and the associated multiphoton Rabi
oscillations in Josephson junctions.Comment: 4 pages, 3 figures; corrected referenc
Multiphoton Antiresonance and Quantum Activation in Driven Systems
We show that nonlinear response of a quantum oscillator displays antiresonant
dips and resonant peaks with varying frequency of the driving field. The effect
is a consequence of special symmetry and is related to resonant multiphoton
mixing of several pairs of oscillator states at a time. We also discuss escape
from a metastable state of forced vibrations. Two important examples show that
the probability of escape via diffusion over quasienergy is larger than via
dynamical tunneling provided the relaxation rate exceeds both of them.
Diffusion dominates even for zero temperature, so that escape occurs via
quantum rather than thermal activation. The effects can be studied using
Josephson junctions and Josephson-junction based systems.Comment: An invited talk at "Unsolved Problems of Noise", 200
Novel Radiation-induced Magnetoresistance Oscillations in a Nondegenerate 2DES on Liquid Helium
We report the observation of novel magnetoresistance oscillations induced by
the resonant inter-subband absorption in nondegenerate 2D electrons bound to
the surface of liquid helium. The oscillations are periodic in 1/B and
originate from the scattering-mediated transitions of the excited electrons
into the Landau states of the first subband. The structure of the oscillations
is affected by the collision broadening of the Landau levels and by
many-electron effects.Comment: 4 figure
Qubit state detection using the quantum Duffing oscillator
We introduce a detection scheme for the state of a qubit, which is based on
resonant few-photon transitions in a driven nonlinear resonator. The latter is
parametrically coupled to the qubit and is used as its detector. Close to the
fundamental resonator frequency, the nonlinear resonator shows sharp resonant
few-photon transitions. Depending on the qubit state, these few-photon
resonances are shifted to different driving frequencies. We show that this
detection scheme offers the advantage of small back action, a large
discrimination power with an enhanced read-out fidelity, and a sufficiently
large measurement efficiency. A realization of this scheme in the form of a
persistent current qubit inductively coupled to a driven SQUID detector in its
nonlinear regime is discussed.Comment: 10 pages, 6 figures. To appear in Phys. Rev.
Relaxation of a qubit measured by a driven Duffing oscillator
We investigate the relaxation of a superconducting qubit for the case when
its detector, the Josephson bifurcation amplifier, remains latched in one of
its two (meta)stable states of forced vibrations. The qubit relaxation rates
are different in different states. They can display strong dependence on the
qubit frequency and resonant enhancement, which is due to quasienergy
resonances. Coupling to the driven oscillator changes the effective temperature
of the qubit.Comment: To appear in Phys. Rev. A (2010
Poisson noise induced switching in driven micromechanical resonators
We study Poisson-noise induced switching between coexisting vibrational
states in driven nonlinear micromechanical resonators. In contrast to Gaussian
noise induced switching, the measured logarithm of the switching rate is
proportional not to the reciprocal noise intensity, but to its logarithm, for
fixed pulse area. We also find that the switching rate logarithm varies as a
square root of the distance to the bifurcation point, instead of the
conventional scaling with exponent 3/2.Comment: accepted by PR
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