574 research outputs found
Strong-coupling branching of FQHL edges
We have developed a theory of quasiparticle backscattering in a system of
point contacts formed between single-mode edges of several Fractional Quantum
Hall Liquids (FQHLs) with in general different filling factors and one
common single-mode edge of another FQHL. In the strong-tunneling limit,
the model of quasiparticle backscattering is obtained by the duality
transformation of the electron tunneling model. The new physics introduced by
the multi-point-contact geometry of the system is coherent splitting of
backscattered quasiparticles at the point contacts in the course of propagation
along the common edge . The ``branching ratios'' characterizing the
splitting determine the charge and exchange statistics of the edge
quasiparticles that can be different from those of Laughlin's quasiparticles in
the bulk of FQHLs. Accounting for the edge statistics is essential for the
system of more than one point contact and requires the proper description of
the flux attachement to tunneling electrons.Comment: 12 pages, 2 figure
Sensitivity and Linearity of Superconducting Radio-Frequency Single-Electron Transistors: Effects of Quantum Charge Fluctuations
We have investigated the effects of quantum fluctuations of quasiparticles on
the operation of superconducting radio-frequency single-electron transistors
(RF-SETs) for large values of the quasiparticle cotunneling parameter
, where and are the Josephson and charging
energies. We find that for , subgap RF-SET operation is still
feasible despite quantum fluctuations that renormalize the SET charging energy
and wash out quasiparticle tunneling thresholds. Surprisingly, such RF-SETs
show linearity and signal-to-noise ratio superior to those obtained when
quantum fluctuations are weak, while still demonstrating excellent charge
sensitivity.Comment: Submitted to Phys. Rev. Let
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
Nonequilibrium and Parity Effects in the Tunneling Conductance of Ultrasmall Superconducting Grains
Recent experiment on the tunneling spectra of ultrasmall superconducting
grains revealed an unusual structure of the lowest differential conductance
peak for grains in the odd charging states. We explain this behavior by
nonequilibrium ``gapless'' excitations associated with different energy levels
occupied by the unpaired electron. These excitations are generated by inelastic
cotunneling.Comment: 4 pages, 2 .eps figures include
Resonant tunneling through a macroscopic charge state in a superconducting SET transistor
We predict theoretically and observe in experiment that the differential
conductance of a superconducting SET transistor exhibits a peak which is a
complete analogue in a macroscopic system of a standard resonant tunneling peak
associated with tunneling through a single quantum state. In particular, in a
symmetric transistor, the peak height is universal and equal to . Away from the resonance we clearly observe the co-tunneling current
which in contrast to the normal-metal transistor varies linearly with the bias
voltage.Comment: 11 pages, 3 figures, Fig. 1 available upon request from the first
autho
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
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
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
Thermal budget of superconducting digital circuits at sub-kelvin temperatures
Superconducting single-flux-quantum (SFQ) circuits have so far been developed
and optimized for operation at or above helium temperatures. The SFQ approach,
however, should also provide potentially viable and scalable control and
read-out circuits for Josephson-junction qubits and other applications with
much lower, milli-kelvin, operating temperatures. This paper analyzes the
overheating problem which becomes important in this new temperature range. We
suggest a thermal model of the SFQ circuits at sub-kelvin temperatures and
present experimental results on overheating of electrons and silicon substrate
which support this model. The model establishes quantitative limitations on the
dissipated power both for "local" electron overheating in resistors and
"global" overheating due to ballistic phonon propagation along the substrate.
Possible changes in the thermal design of SFQ circuits in view of the
overheating problem are also discussed.Comment: 10 pages, 8 figures, submitted to J. Appl. Phy
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