579 research outputs found
Coulomb blockade in superconducting quantum point contacts
Amplitude of the Coulomb blockade oscillations is calculated for a
single-mode Josephson junction with arbitrary electron transparency . It is
shown that the Coulomb blockade is suppressed in ballistic junctions with . The suppression is described quantitatively as the Landau-Zener transition
in imaginary time.Comment: 5 pages, 3 figures include
Resistively-shunted superconducting quantum point contacts
We have studied the Josephson dynamics of resistively-shunted ballistic
superconducting quantum point contacts at finite temperatures and arbitrary
number of conducting modes. Compared to the classical Josephson dynamics of
tunnel junctions, dynamics of quantum point contacts exhibits several new
features associated with temporal fluctuations of the Josephson potential
caused by fluctuations in the occupation of the current-carrying Andreev
levels.Comment: 5 pages, RevTex, 3 postscript figures include
Single-electron transistor effect in a two-terminal structure
A peculiarity of the single-electron transistor effect makes it possible to
observe this effect even in structures lacking a gate electrode altogether. The
proposed method can be useful for experimental study of charging effects in
structures with an extremely small central island confined between tunnel
barriers like a nanometer-sized quantum dot or a macromolecule probed with a
tunneling microscope), where it is impossible to provide a gate electrode for
control of the tunnel current.Comment: 5 pages, 2 figure
Braiding of anyonic quasiparticles in the charge transfer statistics of symmetric fractional edge-state Mach-Zehnder interferometer
We have studied the zero-temperature statistics of the charge transfer
between the two edges of Quantum Hall liquids of, in general, different filling
factors, , with , forming
Mach-Zehnder interferometer. General expression for the cumulant generating
function in the large-time limit is obtained for symmetric interferometer with
equal propagation times along the two edges between the contacts and constant
bias voltage. The low-voltage limit of the generating function can be
interpreted in terms of the regular Poisson process of electron tunneling,
while its leading large-voltage asymptotics is proven to coincide with the
solution of kinetic equation describing quasiparticle transitions between the
states of the interferometer with different effective flux through it,
where . For , this dynamics reflects both the
fractional charge and the fractional statistical angle of the
tunneling quasiparticles. Explicit expressions for the second (shot noise) and
third cumulants are obtained, and their voltage dependence is analyzed.Comment: 11 two-column pages, 4 figure
System of Programmed Modules for Measuring Photographs with a Gamma-Telescope
Physical experiments using tracking cameras resulted in hundreds of thousands of stereo photographs of events being received. To process such a large volume of information, automatic and semiautomatic measuring systems are required. At the Institute of Space Research of the Academy of Science of the USSR, a system for processing film information from the spark gamma-telescope was developed. The system is based on a BPS-75 projector in line with the minicomputer Elektronika 1001. The report describes this system. The various computer programs available to the operators are discussed
Macroscopic Resonant Tunneling in the Presence of Low Frequency Noise
We develop a theory of macroscopic resonant tunneling of flux in a
double-well potential in the presence of realistic flux noise with significant
low-frequency component. The rate of incoherent flux tunneling between the
wells exhibits resonant peaks, the shape and position of which reflect
qualitative features of the noise, and can thus serve as a diagnostic tool for
studying the low-frequency flux noise in SQUID qubits. We show, in particular,
that the noise-induced renormalization of the first resonant peak provides
direct information on the temperature of the noise source and the strength of
its quantum component.Comment: 4 pages, 1 figur
Statistics of the dissipated energy in driven single-electron transitions
We analyze the distribution of heat generated in driven single-electron
transitions and discuss the related non-equilibrium work theorems. In the
adiabatic limit, the heat distribution is shown to become Gaussian, with the
heat noise that, in spite of thermal fluctuations, vanishes together with the
average dissipated energy. We show that the transitions satisfy Jarzynski
equality for arbitrary drive and calculate the probability of the negative heat
values. We also derive a general condition on the heat distribution that
generalizes the Bochkov-Kuzovlev equality and connects it to the Jarzynski
equality.Comment: 5 pages, 2 figure
Transport in the Laughlin quasiparticle interferometer: Evidence for topological protection in an anyonic qubit
We report experiments on temperature and Hall voltage bias dependence of the
superperiodic conductance oscillations in the novel Laughlin quasiparticle
interferometer, where quasiparticles of the 1/3 fractional quantum Hall fluid
execute a closed path around an island of the 2/5 fluid. The amplitude of the
oscillations fits well the quantum-coherent thermal dephasing dependence
predicted for a two point-contact chiral edge channel interferometer in the
full experimental temperature range 10.2<T<141 mK. The temperature dependence
observed in the interferometer is clearly distinct from the behavior in
single-particle resonant tunneling and Coulomb blockade devices. The 5h/e flux
superperiod, originating in the anyonic statistical interaction of Laughlin
quasiparticles, persists to a relatively high T~140 mK. This temperature is
only an order of magnitude less than the 2/5 quantum Hall gap. Such protection
of quantum logic by the topological order of fractional quantum Hall fluids is
expected to facilitate fault-tolerant quantum computation with anyons.Comment: 13 pages, 10 figure
Decoherence in adiabatic quantum computation
We have studied the decoherence properties of adiabatic quantum computation
(AQC) in the presence of in general non-Markovian, e.g., low-frequency, noise.
The developed description of the incoherent Landau-Zener transitions shows that
the global AQC maintains its properties even for decoherence larger than the
minimum gap at the anticrossing of the two lowest energy levels. The more
efficient local AQC, however, does not improve scaling of the computation time
with the number of qubits as in the decoherence-free case. The scaling
improvement requires phase coherence throughout the computation, limiting the
computation time and the problem size n.Comment: 4 pages, 2 figures, published versio
Coherent oscillations in a Cooper-pair box
This paper is devoted to an analysis of the experiment by Nakamura {\it et
al.} (Nature {\bf 398}, 786 (1999)) on the quantum state control in Josephson
junctions devices. By considering the relevant processes involved in the
detection of the charge state of the box and a realistic description of the
gate pulse we are able to analyze some aspects of the experiment (like the
amplitude of the measurement current) in a quantitative way
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