87 research outputs found
Detection of single-electron heat transfer statistics
We consider a quantum dot system whose charge fluctuations are monitored by a
quantum point contact allowing for the detection of both charge and transferred
heat statistics. Our system consists of two nearby conductors that exchange
energy via Coulomb interaction. In interfaces consisting of capacitively
coupled quantum dots, energy transfer is discrete and can be measured by charge
counting statistics. We investigate gate dependent deviations away from a
charge fluctuation theorem in the presence of local temperature gradients (hot
spots). Non universal relations are found for state dependent charge counting.
A fluctuation theorem holds for coupled dot configurations with heat exchange
and no net particle flow.Comment: 6 pages, 3 figures. Published version. Corrected after erratum
publicatio
Glauber coherence of single electron sources
Recently demonstrated solid state single electron sources generate different
quantum states depending on their operation condition. For adiabatic and
non-adiabatic sources we determine the Glauber correlation function in terms of
the Floquet scattering matrix of the source. The correlation function provides
full information on the shape of the state, on its time-dependent amplitude and
phase, which makes the coherence properties of single electron states essential
for the production of quantum multi-particle states.Comment: 4+ pages, 4 figure
Quantum to Classical Transition of the Charge Relaxation Resistance of a Mesoscopic Capacitor
We present an analysis of the effect of dephasing on the single channel
charge relaxation resistance of a mesoscopic capacitor in the linear low
frequency regime. The capacitor consists of a cavity which is via a quantum
point contact connected to an electron reservoir and Coulomb coupled to a gate.
The capacitor is in a perpendicular high magnetic field such that only one
(spin polarized) edge state is (partially) transmitted through the contact. In
the coherent limit the charge relaxation resistance for a single channel
contact is independent of the transmission probability of the contact and given
by half a resistance quantum. The loss of coherence in the conductor is modeled
by attaching to it a fictitious probe, which draws no net current. In the
incoherent limit one could expect a charge relaxation resistance that is
inversely proportional to the transmission probability of the quantum point
contact. However, such a two terminal result requires that scattering is
between two electron reservoirs which provide full inelastic relaxation. We
find that dephasing of a single edge state in the cavity is not sufficient to
generate an interface resistance. As a consequence the charge relaxation
resistance is given by the sum of one constant interface resistance and the
(original) Landauer resistance. The same result is obtained in the high
temperature regime due to energy averaging over many occupied states in the
cavity. Only for a large number of open dephasing channels, describing
spatially homogenous dephasing in the cavity, do we recover the two terminal
resistance, which is inversely proportional to the transmission probability of
the QPC. We compare different dephasing models and discuss the relation of our
results to a recent experiment.Comment: 10 pages, 8 figure
Two-particle non-local Aharonov-Bohm effect from two single-particle emitters
We propose a mesoscopic circuit in the quantum Hall effect regime comprising
two uncorrelated single-particle sources and two distant Mach-Zehnder
interferometers with magnetic fluxes, which allows in a controllable way to
produce orbitally entangled electrons. Two-particle correlations appear as a
consequence of erasing of which path information due to collisions taking place
at distant interferometers and in general at different times. The two-particle
correlations manifest themselves as an Aharonov-Bohm effect in noise while the
current is insensitive to magnetic fluxes. In an appropriate time-interval the
concurrence reaches a maximum and a Bell inequality is violated.Comment: 4 pages, 2 figures, published in Phys. Rev. Let
Quantum Nondemolition Measurement of a Kicked Qubit
We propose a quantum nondemolition measurement using a kicked two-state
system (qubit). By tuning the waiting time between kicks to be the qubit
oscillation period, the kicking apparatus performs a nondemolition measurement.
While dephasing is unavoidable, the nondemolition measurement can (1) slow
relaxation of diagonal density matrix elements, (2) avoid detector back-action,
and (3) allow for a large signal-to-noise ratio. Deviations from the ideal
behavior are studied by allowing for detuning of the waiting time, as well as
finite-time, noisy pulses. The scheme is illustrated with a double-dot qubit
measured by a gate-pulsed quantum point contact.Comment: 7 pages, 1 figur
Mesoscopic Capacitance Oscillations
We examine oscillations as a function of Fermi energy in the capacitance of a
mesoscopic cavity connected via a single quantum channel to a metallic contact
and capacitively coupled to a back gate. The oscillations depend on the
distribution of single levels in the cavity, the interaction strength and the
transmission probability through the quantum channel. We use a Hartree-Fock
approach to exclude self-interaction. The sample specific capacitance
oscillations are in marked contrast to the charge relaxation resistance, which
together with the capacitance defines the RC-time, and which for spin polarized
electrons is quantized at half a resistance quantum. Both the capacitance
oscillations and the quantized charge relaxation resistance are seen in a
strikingly clear manner in a recent experiment.Comment: 9 pages, 2 figure
Local non-equilibrium distribution of charge carriers in a phase-coherent conductor
We use the scattering matrix approach to derive generalized Bardeen-like
formulae for the conductances between the contacts of a phase-coherent
multiprobe conductor and a tunneling tip which probes its surface. These
conductances are proportional to local partial densities of states, called
injectivities and emissivities. The current and the current fluctuations
measured at the tip are related to an effective local non-equilibrium
distribution function. This distribution function contains the
quantum-mechanical phase-coherence of the charge carriers in the conductor and
is given as products of injectivities and the Fermi distribution functions in
the electron reservoirs. The results are illustrated for measurements on
ballistic conductors with barriers and for diffusive conductors.Comment: 4 pages, 2 figures, submitted to "Comptes Rendus de l'Academie des
Sciences
Coherence of Single Electron Sources from Mach-Zehnder Interferometry
A new type of electron sources has emerged which permits to inject particles
in a controllable manner, one at a time, into an electronic circuit. Such
single electron sources make it possible to fully exploit the particles'
quantum nature. We determine the single-particle coherence length from the
decay of the Aharonov-Bohm oscillations as a function of the imbalance of a
Mach-Zehnder interferometer connected to a single electron source. The
single-particle coherence length is of particular importance as it is an
intrinsic property of the source in contrast to the dephasing length.Comment: 4 pages, 4 figure
- …