658 research outputs found
Imaging and manipulating electrons in a 1D quantum dot with Coulomb blockade microscopy
Motivated by the recent experiments by the Westervelt group using a mobile
tip to probe the electronic state of quantum dots formed on a segmented
nanowire, we study the shifts in Coulomb blockade peak positions as a function
of the spatial variation of the tip potential, which can be termed "Coulomb
blockade microscopy". We show that if the tip can be brought sufficiently close
to the nanowire, one can distinguish a high density electronic liquid state
from a Wigner crystal state by microscopy with a weak tip potential. In the
opposite limit of a strongly negative tip potential, the potential depletes the
electronic density under it and divides the quantum wire into two partitions.
There the tip can push individual electrons from one partition to the other,
and the Coulomb blockade micrograph can clearly track such transitions. We show
that this phenomenon can be used to qualitatively estimate the relative
importance of the electron interaction compared to one particle potential and
kinetic energies. Finally, we propose that a weak tip Coulomb blockade
micrograph focusing on the transition between electron number N=0 and N=1
states may be used to experimentally map the one-particle potential landscape
produced by impurities and inhomogeneities.Comment: 4 pages 7 figure
Lipid Raft-Mediated Regulation of G-Protein Coupled Receptor Signaling by Ligands which Influence Receptor Dimerization: A Computational Study
G-protein coupled receptors (GPCRs) are the largest family of cell surface receptors; they activate heterotrimeric G-proteins in response to ligand stimulation. Although many GPCRs have been shown to form homo- and/or heterodimers on the cell membrane, the purpose of this dimerization is not known. Recent research has shown that receptor dimerization may have a role in organization of receptors on the cell surface. In addition, microdomains on the cell membrane termed lipid rafts have been shown to play a role in GPCR localization. Using a combination of stochastic (Monte Carlo) and deterministic modeling, we propose a novel mechanism for lipid raft partitioning of GPCRs based on reversible dimerization of receptors and then demonstrate that such localization can affect GPCR signaling. Modeling results are consistent with a variety of experimental data indicating that lipid rafts have a role in amplification or attenuation of G-protein signaling. Thus our work suggests a new mechanism by which dimerization-inducing or inhibiting characteristics of ligands can influence GPCR signaling by controlling receptor organization on the cell membrane
Quantum Teleportation from a Propagating Photon to a Solid-State Spin Qubit
The realization of a quantum interface between a propagating photon used for
transmission of quantum information, and a stationary qubit used for storage
and manipulation, has long been an outstanding goal in quantum information
science. A method for implementing such an interface between dissimilar qubits
is quantum teleportation, which has attracted considerable interest not only as
a versatile quantum-state-transfer method but also as a quantum computational
primitive. Here, we experimentally demonstrate transfer of quantum information
carried by a photonic qubit to a quantum dot spin qubit using quantum
teleportation. In our experiment, a single photon in a superposition state of
two colors -- a photonic qubit is generated using selective resonant excitation
of a neutral quantum dot. We achieve an unprecedented degree of
indistinguishability of single photons from different quantum dots by using
local electric and magnetic field control. To teleport a photonic qubit, we
generate an entangled spin-photon state in a second quantum dot located 5
meters away from the first and interfere the photons from the two dots in a
Hong-Ou-Mandel set-up. A coincidence detection at the output of the
interferometer heralds successful teleportation, which we verify by measuring
the resulting spin state after its coherence time is prolonged by an optical
spin-echo pulse sequence. The demonstration of successful inter-conversion of
photonic and semiconductor spin qubits constitute a major step towards the
realization of on-chip quantum networks based on semiconductor nano-structures.Comment: 12 pages, 3 figures, Comments welcom
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