203 research outputs found
Noise correlations, entanglement, and Bell inequalities
The aim of this chapter is to describe two situations where positive noise
correlations can be directly monitored using a transport experiment, either
with a superconductor or with a correlated electron system. To be more precise,
the present text reflects the presentations made by the three authors during
the Delft NATO workshop. Bell inequalities and quantum mechanical non-locality
with electrons injected from a superconductor will be addressed first. Next,
noise correlations will be computed in a carbon nanotube where electrons are
injected in the bulk from a STM tip. The first topic is the result of an
ongoing collaboration with G. Lesovik and G. Blatter over the years. The
unifying theme is that in both branched quantum circuits, entanglement is
explicit and can be illustrated via noise correlations. Entanglement can be
achieved either for pairs of electrons in the case of superconductor sources
connected to Fermi liquid leads, or alternatively for pairs of quasiparticle
excitations of the correlated electron fluid.Comment: 24 pages, 7 figures, Proceedings of the NATO ARW workshop on Quantum
Noise, Y. Nazarov and Y. Blanter editors (Kluwer 2002
Photo-assisted shot noise in the fractional quantum Hall regime
The effect of an ac perturbation on the shot noise of a fractional quantum
Hall fluid is studied at finite temperature. For a normal metal, it is known
that the zero-frequency noise derivative exhibits steps as a function of bias
voltage. In contrast, at Laughlin fractions, the backscattering noise exhibits
evenly spaced singularities, which are reminiscent of tunneling
density-of-states singularities for quasiparticles. The spacing is determined
by the quasiparticle charge and the ratio of the dc bias with respect
to the drive frequency. Photo-assisted transport can thus be considered as a
probe for effective charges of the quantum Hall effect.Comment: Proceeding of the 18th International Conference on Noise and
Fluctuations, Salamanca, Spai
Measurement of finite frequency noise cross-correlations with a resonant circuit
The measurement of finite frequency noise cross-correlations represents an
experimental challenge in mesoscopic physics. Here we propose a generalisation
of the resonant LC circuit setup of Lesovik and Loosen which allow to probe
directly such cross-correlations by measuring the charge fluctuations on the
plates of a capacitor. The measuring circuit collects noise contributions at
the resonant frequency of the LC circuit. Auto-correlation noise can be
canceled out by switching the wires and making two distinct measurements. The
measured cross-correlations then depend of four non-symmetrized correlators.
This detection method is applied to a normal metal three terminal device. We
subsequently discuss to what extent the measurement circuit can detect
electron-antibunching and what singularities appear in the spectral density of
noise cross-correlations
Anomalous Hall effect in ferromagnetic disordered metals
The anomalous Hall effect in disordered band ferromagnets is considered in
the framework of quantum transport theory. A microscopic model of electrons in
a random potential of identical impurities including spin-orbit coupling is
used. The Hall conductivity is calculated from the Kubo formula for both, the
skew scattering and the side-jump mechanisms. The recently discussed Berry
phase induced Hall current is also evaluated within the model. The effect of
strong impurity scattering is analyzed and it is found to affect the ratio of
the non-diagonal (Hall) and diagonal components of the conductivity as well as
the relative importance of different mechanisms.Comment: Invited paper for Ann. Physik commemorating Paul Drud
Photo-assisted shot noise in Coulomb interacting systems
We consider the fluctuations of the electrical current (shot noise) in the
presence of a voltage time-modulation. For a non-interacting metal, it is known
that the derivative of the photo-assisted noise has a staircase behavior. In
the presence of Coulomb interactions, we show that the photo-assisted noise
presents a more complex profile, in particular for the two following systems:
1) a two-dimensional electron gas in the fractional quantum Hall regime for
which we have obtained evenly spaced singularities in the noise derivative,
with a spacing related to the filling factor and, 2) a carbon nanotube for
which a smoothed staircase in the noise derivative is obtained.Comment: Proceedings of the 6th Rencontres du Vietnam, Hanoi (2006
Quantum dot dephasing by fractional quantum Hall edge states
We consider the dephasing rate of an electron level in a quantum dot, placed
next to a fluctuating edge current in the fractional quantum Hall effect. Using
perturbation theory, we show that this rate has an anomalous dependence on the
bias voltage applied to the neighboring quantum point contact, which originates
from the Luttinger liquid physics which describes the Hall fluid. General
expressions are obtained using a screened Coulomb interaction. The dephasing
rate is strictly proportional to the zero frequency backscattering current
noise, which allows to describe exactly the weak to strong backscattering
crossover using the Bethe-Ansatz solution
Follicle-stimulating hormone (FSH) activates extracellular signal-regulated kinase phosphorylation independently of beta-arrestin- and dynamin-mediated FSH receptor internalization
BACKGROUND: The follicle-stimulating hormone receptor (FSH-R) is a seven transmembrane spanning receptor (7TMR) which plays a crucial role in male and female reproduction. Upon FSH stimulation, the FSH-R activates the extracellular signal-regulated kinases (ERK). However, the mechanisms whereby the agonist-stimulated FSH-R activates ERK are poorly understood. In order to activate ERK, some 7 TMRs require beta-arrestin-and dynamin-dependent internalization to occur, whereas some others do not. In the present study, we examined the ability of the FSH-activated FSH-R to induce ERK phosphorylation, in conditions where its beta-arrestin- and dynamin-mediated internalization was impaired. METHODS: Human embryonic kidney (HEK) 293 cells were transiently transfected with the rat FSH-R. Internalization of the FSH-R was manipulated by co-expression of either a beta-arrestin (319–418) dominant negative peptide, either an inactive dynamin K44A mutant or of wild-type beta-arrestin 1 or 2. The outcomes on the FSH-R internalization were assayed by measuring 125I-FSH binding at the cell surface when compared to internalized 125I-FSH binding. The resulting ERK phosphorylation level was visualized by Western blot analysis. RESULTS: In HEK 293 cells, FSH stimulated ERK phosphorylation in a dose-dependent manner. Co-transfection of the beta- arrestin (319–418) construct, or of the dynamin K44A mutant reduced FSH-R internalization in response to FSH, without affecting ERK phosphorylation. Likewise, overexpression of wild-type beta-arrestin 1 or 2 significantly increased the FSH-R internalization level in response to FSH, without altering FSH-induced ERK phosphorylation. CONCLUSION: From these results, we conclude that the FSH-R does not require beta-arrestin- nor dynamin-mediated internalization to initiate ERK phosphorylation in response to FSH
Towards the convergent therapeutic potential of GPCRs in autism spectrum disorders
Changes in genetic and/or environmental factors to developing neural circuits
and subsequent synaptic functions are known to be a causative underlying the
varied socio-emotional behavioural patterns associated with autism spectrum
disorders (ASD). Seven transmembrane G protein-coupled receptors (GPCRs)
comprising the largest family of cell-surface receptors, mediate the transfer
of extracellular signals to downstream cellular responses. Disruption of GPCR
and their signalling have been implicated as a convergent pathologic mechanism
of ASD. Here, we aim to review the literature about the 23 GPCRs that are
genetically associated to ASD pathology according to Simons Foundation Autism
Research Initiative (SFARI) database such as oxytocin (OXTR) and vasopressin
(V1A, V1B) receptors, metabotropic glutamate (mGlu5, mGlu7) and
gamma-aminobutyric acid (GABAB) receptors, dopamine (D1, D2), serotoninergic
(5-HT1B and additionally included the 5-HT2A, 5-HT7 receptors for their strong
relevance to ASD), adrenergic (2) and cholinergic (M3) receptors,
adenosine (A2A, A3) receptors, angiotensin (AT2) receptors, cannabinoid (CB1)
receptors, chemokine (CX3CR1) receptors, orphan (GPR37, GPR85) and olfactory
(OR1C1, OR2M4, OR2T10, OR52M1) receptors. We discussed the genetic variants,
relation to core ASD behavioural deficits and update on pharmacological
compounds targeting these 23 GPCRs. Of these OTR, V1A, mGlu5, D2, 5-HT2A, CB1,
and GPR37 serve as the best therapeutic targets and have potential towards core
domains of ASD pathology. With a functional crosstalk between different GPCRs
and converging pharmacological responses, there is an urge to develop novel
therapeutic strategies based on multiple GPCRs to reduce the socioeconomic
burden associated with ASD and we strongly emphasize the need to prioritize the
increased clinical trials targeting the multiple GPCRs
Transient thermoelectricity in a vibrating quantum dot in Kondo regime
We investigate the time evolution of the thermopower in a vibrating quantum
dot suddenly shifted into the Kondo regime via a gate voltage by adopting the
time-dependent non-crossing approximation and linear response Onsager
relations. Behaviour of the instantaneous thermopower is studied for a range of
temperatures both in zero and strong electron-phonon coupling. We argue that
inverse of the saturation value of decay time of thermopower to its steady
state value might be an alternative tool in determination of the Kondo
temperature and the value of the electron-phonon coupling strength.Comment: 5 pages, 4 figures, to appear in Physics Letters
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