1,419 research outputs found
Persistent Rabi oscillations probed via low-frequency noise correlation
The qubit Rabi oscillations are known to be non-decaying (though with a
fluctuating phase) if the qubit is continuously monitored in the weak-coupling
regime. In this paper we propose an experiment to demonstrate these persistent
Rabi oscillations via low-frequency noise correlation. The idea is to measure a
qubit by two detectors, biased stroboscopically at the Rabi frequency. The
low-frequency noise depends on the relative phase between the two combs of
biasing pulses, with a strong increase of telegraph noise in both detectors for
the in-phase or anti-phase combs. This happens because of self-synchronization
between the persistent Rabi oscillations and measurement pulses. Almost perfect
correlation of the noise in the two detectors for the in-phase regime and
almost perfect anticorrelation for the anti-phase regime indicates a presence
of synchronized persistent Rabi oscillations. The experiment can be realized
with semiconductor or superconductor qubits.Comment: 5 page
Crossover of phase qubit dynamics in presence of negative-result weak measurement
Coherent dynamics of a superconducting phase qubit is considered in the
presence of both unitary evolution due to microwave driving and continuous
non-unitary collapse due to negative-result measurement. In the case of a
relatively weak driving, the qubit dynamics is dominated by the non-unitary
evolution, and the qubit state tends to an asymptotically stable point on the
Bloch sphere. This dynamics can be clearly distinguished from conventional
decoherence by tracking the state purity and the measurement invariant
(``murity''). When the microwave driving strength exceeds certain critical
value, the dynamics changes to non-decaying oscillations: any initial state
returns exactly to itself periodically in spite of non-unitary dynamics. The
predictions can be verified using a modification of a recent experiment.Comment: 5 pages, 4 eps figure
Systematic Effects in Interferometric Observations of the CMB Polarization
The detection of the primordial -mode spectrum of the polarized cosmic
microwave background (CMB) signal may provide a probe of inflation. However,
observation of such a faint signal requires excellent control of systematic
errors. Interferometry proves to be a promising approach for overcoming such a
challenge. In this paper we present a complete simulation pipeline of
interferometric observations of CMB polarization, including systematic errors.
We employ two different methods for obtaining the power spectra from mock data
produced by simulated observations: the maximum likelihood method and the
method of Gibbs sampling. We show that the results from both methods are
consistent with each other, as well as, within a factor of 6, with analytical
estimates. Several categories of systematic errors are considered: instrumental
errors, consisting of antenna gain and antenna coupling errors, and beam
errors, consisting of antenna pointing errors, beam cross-polarization and beam
shape (and size) errors. In order to recover the tensor-to-scalar ratio, ,
within a 10% tolerance level, which ensures the experiment is sensitive enough
to detect the -signal at in the multipole range ,
we find that, for a QUBIC-like experiment, Gaussian-distributed systematic
errors must be controlled with precisions of for antenna
gain, for antenna coupling, for pointing, for beam
shape, and for beam cross-polarization.Comment: 15 pages, 6 figures, submitted to ApJ
A Numerical Study of Transport and Shot Noise at 2D Hopping
We have used modern supercomputer facilities to carry out extensive Monte
Carlo simulations of 2D hopping (at negligible Coulomb interaction) in
conductors with the completely random distribution of localized sites in both
space and energy, within a broad range of the applied electric field and
temperature , both within and beyond the variable-range hopping region. The
calculated properties include not only dc current and statistics of localized
site occupation and hop lengths, but also the current fluctuation spectrum.
Within the calculation accuracy, the model does not exhibit noise, so
that the low-frequency noise at low temperatures may be characterized by the
Fano factor . For sufficiently large samples, scales with conductor
length as , where , and
parameter is interpreted as the average percolation cluster length. At
relatively low , the electric field dependence of parameter is
compatible with the law which follows from directed
percolation theory arguments.Comment: 17 pages, 8 figures; Fixed minor typos and updated reference
Quantum Dynamics in Non-equilibrium Strongly Correlated Environments
We consider a quantum point contact between two Luttinger liquids coupled to
a mechanical system (oscillator). For non-vanishing bias, we find an effective
oscillator temperature that depends on the Luttinger parameter. A generalized
fluctuation-dissipation relation connects the decoherence and dissipation of
the oscillator to the current-voltage characteristics of the device. Via a
spectral representation, this result is generalized to arbitrary leads in a
weak tunneling regime.Comment: 4 pages, 1 figur
Charge and current fluctuations in a superconducting single electron transistor near a Cooper pair resonance
We analyze charge tunneling statistics and current noise in a superconducting
single-electron transistor in a regime where the Josephson-quasiparticle cycle
is the dominant mechanism of transport. Due to the interplay between Coulomb
blockade and Josephson coherence, the probability distribution for tunneling
events strongly deviates from a Poissonian and displays a pronounced even--odd
asymmetry in the number of transmitted charges. The interplay between charging
and coherence is reflected also in the zero-frequency current noise which is
significantly quenched when the quasi-particle tunneling rates are comparable
to the coherent Cooper-pair oscillation frequency. Furthermore the finite
frequency spectrum shows a strong enhancement near the resonant transition
frequency for Josephson tunneling.Comment: 10 pages, 11 figure
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