39 research outputs found
Partly noiseless encoding of quantum information in quantum dot arrays against phonon-induced pure dephasing
We show that pure dephasing of a quantum dot charge (excitonic) qubit may be
reduced for sufficiently slow gating by collectively encoding quantum
information in an array of quantum dots. We study the role of the size and
structure of the array and of the exciton lifetime for the resulting total
error of a single-qubit operation.Comment: Final version; 10 pages, 8 figure
Interplay and optimization of decoherence mechanisms in the optical control of spin quantum bits implemented on a semiconductor quantum dot
We study the influence of the environment on an optically induced rotation of
a single electron spin in a charged semiconductor quantum dot. We analyze the
decoherence mechanisms resulting from the dynamical lattice response to the
charge evolution induced in a trion-based optical spin control scheme.
Moreover, we study the effect of the finite trion lifetime and of the
imperfections of the unitary evolution such as off-resonant excitations and the
nonadiabaticity of the driving. We calculate the total error of the operation
on a spin-based qubit in an InAs/GaAs quantum dot system and discuss possible
optimization against the different contributions. We indicate the parameters
which allow for coherent control of the spin with a single qubit gate error as
low as .Comment: Final version, 14 pages, 11 figure
Heat pumping with optically driven excitons
We present a theoretical study showing that an optically driven excitonic
two-level system in a solid state environment acts as a heat pump by means of
repeated phonon emission or absorption events. We derive a master equation for
the combined phonon bath and two-level system dynamics and analyze the
direction and rate of energy transfer as a function of the externally
accessible driving parameters. We discover that if the driving laser is detuned
from the exciton transition, cooling the phonon environment becomes possible
Exciton spin-flip rate in quantum dots determined by a modified local density of optical states
The spin-flip rate that couples dark and bright excitons in self-assembled
quantum dots is obtained from time-resolved spontaneous emission measurements
in a modified local density of optical states. Employing this technique, we can
separate effects due to non-radiative recombination and unambiguously record
the spin-flip rate. The dependence of the spin-flip rate on emission energy is
compared in detail to a recent model from the literature, where the spin flip
is due to the combined action of short-range exchange interaction and acoustic
phonons. We furthermore observe a surprising enhancement of the spin-flip rate
close to a semiconductor-air interface, which illustrates the important role of
interfaces for quantum dot based nanophotonic structures. Our work is an
important step towards a full understanding of the complex dynamics of quantum
dots in nanophotonic structures, such as photonic crystals, and dark excitons
are potentially useful for long-lived coherent storage applications.Comment: 5 pages, 4 figure
Theory of Spin Relaxation in Two-Electron Lateral Coupled Si/SiGe Quantum Dots
Highly accurate numerical results of phonon-induced two-electron spin
relaxation in silicon double quantum dots are presented. The relaxation,
enabled by spin-orbit coupling and the nuclei of Si (natural or purified
abundance), are investigated for experimentally relevant parameters, the
interdot coupling, the magnetic field magnitude and orientation, and the
detuning. We calculate relaxation rates for zero and finite temperatures (100
mK), concluding that our findings for zero temperature remain qualitatively
valid also for 100 mK. We confirm the same anisotropic switch of the axis of
prolonged spin lifetime with varying detuning as recently predicted in GaAs.
Conditions for possibly hyperfine-dominated relaxation are much more stringent
in Si than in GaAs. For experimentally relevant regimes, the spin-orbit
coupling, although weak, is the dominant contribution, yielding anisotropic
relaxation rates of at least two order of magnitude lower than in GaAs.Comment: 11 pages, 10 figure
Phonon-induced decoherence for a quantum dot spin qubit operated by Raman passage
We study single-qubit gates performed via stimulated Raman adiabatic passage
(STIRAP) on a spin qubit implemented in a quantum dot system in the presence of
phonons. We analyze the interplay of various kinds of errors resulting from the
carrier-phonon interaction as well as from quantum jumps related to
nonadiabaticity and calculate the fidelity as a function of the pulse
parameters. We give quantitative estimates for an InAs/GaAs system and identify
the parameter values for which the error is considerably minimized, even to
values below per operation.Comment: Final version; considerable extensions; 18 pages, 7 figure
Theory of 'which path' dephasing in single electron interference due to trace in conductive environment
A single-electron two-path interference (Young) experiment is considered
theoretically. The decoherence of an electron wave packet due to the 'which
path' trace left in the conducting (metallic) plate placed under the electron
trajectories is calculated using the many-body quantum description of the
electron gas reservoir.Comment: 11 pages, 5 figures, moderate changes, 1 new figure, updated
reference
One-step immunopurification and lectinochemical characterization of the Duffy atypical chemokine receptor from human erythrocytes
Duffy antigen/receptor for chemokines (DARC) is a glycosylated seven-transmembrane protein acting as a blood group antigen, a chemokine binding protein and a receptor for Plasmodium vivax malaria parasite. It is present on erythrocytes and endothelial cells of postcapillary venules. The N-terminal extracellular domain of the Duffy glycoprotein carries Fya/Fyb blood group antigens and Fy6 linear epitope recognized by monoclonal antibodies. Previously, we have shown that recombinant Duffy protein expressed in K562 cells has three N-linked oligosaccharide chains, which are mainly of complex-type. Here we report a one-step purification method of Duffy protein from human erythrocytes. DARC was extracted from erythrocyte membranes in the presence of 1% n-dodecyl-β-D-maltoside (DDM) and 0.05% cholesteryl hemisuccinate (CHS) and purified by affinity chromatography using immobilized anti-Fy6 2C3 mouse monoclonal antibody. Duffy glycoprotein was eluted from the column with synthetic DFEDVWN peptide containing epitope for 2C3 monoclonal antibody. In this single-step immunoaffinity purification method we obtained highly purified DARC, which migrates in SDS-polyacrylamide gel as a major diffuse band corresponding to a molecular mass of 40–47 kDa. In ELISA purified Duffy glycoprotein binds anti-Duffy antibodies recognizing epitopes located on distinct regions of the molecule. Results of circular dichroism measurement indicate that purified DARC has a high content of α-helical secondary structure typical for chemokine receptors. Analysis of DARC glycans performed by means of lectin blotting and glycosidase digestion suggests that native Duffy N-glycans are mostly triantennary complex-type, terminated with α2-3- and α2-6-linked sialic acid residues with bisecting GlcNAc and α1-6-linked fucose at the core