17 research outputs found
Three-level mixing and dark states in transport through quantum dots
We consider theoretically the transport through the double quantum dot
structure of the recent experiment of C. Payette {\it et al.} [Phys. Rev. Lett.
{\bf 102}, 026808 (2009)] and calculate stationary current and shotnoise.
Three-level mixing gives rise to a pronounced current suppression effect, the
character of which charges markedly with bias direction. We discuss these
results in connexion with the dark states of coherent population trapping in
quantum dots.Comment: 6 pages, 5 fig
Scanning gate experiments: from strongly to weakly invasive probes
An open resonator fabricated in a two-dimensional electron gas is used to
explore the transition from strongly invasive scanning gate microscopy to the
perturbative regime of weak tip-induced potentials. With the help of numerical
simulations that faithfully reproduce the main experimental findings, we
quantify the extent of the perturbative regime in which the tip-induced
conductance change is unambiguously determined by properties of the unperturbed
system. The correspondence between the experimental and numerical results is
established by analyzing the characteristic length scale and the amplitude
modulation of the conductance change. In the perturbative regime, the former is
shown to assume a disorder-dependent maximum value, while the latter linearly
increases with the strength of a weak tip potential.Comment: 11 pages, 7 figure
Reverse quantum state engineering using electronic feedback loops
We propose an all-electronic technique to manipulate and control interacting
quantum systems by unitary single-jump feedback conditioned on the outcome of a
capacitively coupled electrometer and in particular a single-electron
transistor. We provide a general scheme to stabilize pure states in the quantum
system and employ an effective Hamiltonian method for the quantum master
equation to elaborate on the nature of stabilizable states and the conditions
under which state purification can be achieved. The state engineering within
the quantum feedback scheme is shown to be linked with the solution of an
inverse eigenvalue problem. Two applications of the feedback scheme are
presented in detail: (i) stabilization of delocalized pure states in a single
charge qubit and (ii) entanglement stabilization in two coupled charge qubits.
In the latter example we demonstrate the stabilization of a maximally entangled
Bell state for certain detector positions and local feedback operations.Comment: 23 pages, 6 figures, to be published by New Journal of Physics (2013
Uma abordagem heurĂstica para a programação da produção na indĂșstria de fundição com utilização da lĂłgica fuzzy
Quantitative Organization of GABAergic Synapses in the Molecular Layer of the Mouse Cerebellar Cortex
In the cerebellar cortex, interneurons of the molecular layer (stellate and basket cells) provide GABAergic input to Purkinje cells, as well as to each other and possibly to other interneurons. GABAergic inhibition in the molecular layer has mainly been investigated at the interneuron to Purkinje cell synapse. In this study, we used complementary subtractive strategies to quantitatively assess the ratio of GABAergic synapses on Purkinje cell dendrites versus those on interneurons. We generated a mouse model in which the GABAA receptor α1 subunit (GABAARα1) was selectively removed from Purkinje cells using the Cre/loxP system. Deletion of the α1 subunit resulted in a complete loss of GABAAR aggregates from Purkinje cells, allowing us to determine the density of GABAAR clusters in interneurons. In a complementary approach, we determined the density of GABA synapses impinging on Purkinje cells using α-dystroglycan as a specific marker of inhibitory postsynaptic sites. Combining these inverse approaches, we found that synapses received by interneurons represent approximately 40% of all GABAergic synapses in the molecular layer. Notably, this proportion was stable during postnatal development, indicating synchronized synaptogenesis. Based on the pure quantity of GABAergic synapses onto interneurons, we propose that mutual inhibition must play an important, yet largely neglected, computational role in the cerebellar cortex
Analysis of zwitterionic and anionic N-linked glycans from invertebrates and protists by mass spectrometry
Affinity of various benzodiazepine site ligands in mice with a point mutation in the GABA A receptor Îł2 subunit
Abstract The benzodiazepine binding site of GABA A receptors is located at the interface of the a and g subunits. Certain point mutations in these subunits have been demonstrated to dramatically reduce the affinity of benzodiazepine binding site ligands for these receptors. Recently, mice were generated with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the g2 subunit of GABA A receptors. Here we tested the potency of 24 benzodiazepine binding site ligands from 16 different structural classes for inhibition of [ 3 H]flunitrazepam binding to brain membranes of these g2F77I mice. Results indicate that the potency of the classical 1,4-benzodiazepines, of the 1,4-thienodiazepine clotiazepam, the 1,5-benzodiazepine clobazam, or the pyrazoloquinoline CGS 9896 is only 2-7-fold reduced by this g2F77I point mutation. The potency of the imidazopyrimidines Ru 32698, Ru 33203, and Ru 33356, of the imidazoquinoline Ru 31719, or the pyrazolopyridine CGS 20625 is reduced 10-20-fold, whereas the potency of some imidazobenzodiazepines, b-carbolines, cyclopyrrolones, imidazopyridines, triazolopyridazines, or quinolines is 100-1000-fold reduced. Interestingly, the extent of potency reduction induced by the g2F77I point mutation varied within the structural classes of compounds. Results support and significantly extend previous observations indicating that the residue g2F77 is important for high affinity binding of some, but not all benzodiazepine site ligands