312 research outputs found
Deconfinement transition and dimensional crossover in the Bechgaard-Fabre salts: pressure- and temperature-dependent optical investigations
The infrared response of the organic conductor (TMTSF)PF and the Mott
insulator (TMTTF)PF are investigated as a function of temperature and
pressure and for the polarization parallel and perpendicular to the molecular
stacks. By applying external pressure on (TMTTF)PF, the Mott gap
rapidly diminishes until the deconfinement transition occurs when the gap
energy is approximately twice the interchain transfer integral. In its
deconfined state (TMTTF)PF exhibits a crossover from a
quasi-one-dimensional to a higher-dimensional metal upon reducing the
temperature. For (TMTSF)PF this dimensional crossover is observed
either with increase in external pressure or with decrease in temperature. We
quantitatively determine the dimensional crossover line in the
pressure-temperature diagram based on the degree of coherence in the optical
response perpendicular to the molecular stacks.Comment: 12 pages, 15 figure
Charge echo in a Cooper-pair box
A spin-echo-type technique is applied to an artificial two-level system that
utilizes charge degree of freedom in a small superconducting electrode.
Gate-voltage pulses are used to produce the necessary pulse sequence in order
to eliminate the inhomogeneity effect in the time-ensemble measurement and to
obtain refocused echo signals. Comparison of the decay time of the observed
echo signal with estimated decoherence time suggests that low-frequency
energy-level fluctuations due to the 1/f charge noise dominate the dephasing in
the system.Comment: 4 pages, 3 figure
Quantum noise in the Josephson charge qubit
We study decoherence of the Josephson charge qubit by measuring energy
relaxation and dephasing with help of the single-shot readout. We found that
the dominant energy relaxation process is a spontaneous emission induced by
quantum noise coupled to the charge degree of freedom. Spectral density of the
noise at high frequencies is roughly proportional to the qubit excitation
energy.Comment: Submitted to Phys. Rev. Letter
Parity effect in superconducting aluminum single electron transistors with spatial gap profile controlled by film thickness
We propose a novel method for suppression of quasiparticle poisoning in Al
Coulomb blockade devices. The method is based on creation of a proper energy
gap profile along the device. In contrast to the previously used techniques,
the energy gap is controlled by the film thickness. Our transport measurements
confirm that the quasiparticle poisoning is suppressed and clear 2
periodicity is observed only when the island is made much thinner than the
leads. This result is consistent with the existing model and provides a simple
method to suppress quasiparticle poisoning
Electromagnetically induced transparency on a single artificial atom
We present experimental observation of electromagnetically induced
transparency (EIT) on a single macroscopic artificial "atom" (superconducting
quantum system) coupled to open 1D space of a transmission line. Unlike in a
optical media with many atoms, the single atom EIT in 1D space is revealed in
suppression of reflection of electromagnetic waves, rather than absorption. The
observed almost 100 % modulation of the reflection and transmission of
propagating microwaves demonstrates full controllability of individual
artificial atoms and a possibility to manipulate the atomic states. The system
can be used as a switchable mirror of microwaves and opens a good perspective
for its applications in photonic quantum information processing and other
fields
Single-electron current sources: towards a refined definition of ampere
Controlling electrons at the level of elementary charge has been
demonstrated experimentally already in the 1980's. Ever since, producing an
electrical current , or its integer multiple, at a drive frequency has
been in a focus of research for metrological purposes. In this review we first
discuss the generic physical phenomena and technical constraints that influence
charge transport. We then present the broad variety of proposed realizations.
Some of them have already proven experimentally to nearly fulfill the demanding
needs, in terms of transfer errors and transfer rate, of quantum metrology of
electrical quantities, whereas some others are currently "just" wild ideas,
still often potentially competitive if technical constraints can be lifted. We
also discuss the important issues of read-out of single-electron events and
potential error correction schemes based on them. Finally, we give an account
of the status of single-electron current sources in the bigger framework of
electric quantum standards and of the future international SI system of units,
and briefly discuss the applications and uses of single-electron devices
outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references,
reworded the section on AC pump
Dynamics of coherent and incoherent emission from an artificial atom in a 1D space
We study dynamics of an artificial two-level atom in an open 1D space by
measuring evolution of its coherent and incoherent emission. States of the atom
-- a superconducting flux qubit coupled to a transmission line -- are fully
controlled by resonant excitation microwave pulses. The coherent emission -- a
direct measure of superposition in the atom -- exhibits decaying oscillations
shifted by from oscillations of the incoherent emission, which, in
turn, is proportional to the atomic population. The emission dynamics provides
information about states and properties of the atom. By measuring the coherent
dynamics, we derive two-time correlation function of fluctuations and, using
quantum regression formula, reconstruct the incoherent spectrum of the
resonance fluorescence triplet, which is in a good agreement with the directly
measured one.Comment: 4 pages, 4 figure
Temperature square dependence of the low frequency 1/f charge noise in the Josephson junction qubits
To verify the hypothesis about the common origin of the low frequency 1/f
noise and the quantum f noise recently measured in the Josephson charge qubits,
we study temperature dependence of the 1/f noise and decay of coherent
oscillations. T^2 dependence of the 1/f noise is experimentally demonstrated,
which supports the hypothesis. We also show that dephasing in the Josephson
charge qubits off the electrostatic energy degeneracy point is consistently
explained by the same low frequency 1/f noise that is observed in the transport
measurements.Comment: 4 pages, 2 figure
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