728 research outputs found
SYNTHESIS AND STYRENE COPOLYMERIZATION OF OCTYL 2-CYANO-3-(R-PHENYL)-2-PROPENOATES
Novel alkyl ring-substituted octyl phenylcyanoacrylates (OPCA), RPhCH=C(CN)CO2CH2(CH2)6CH3, where R is H, 2-methyl, 3-methyl, 4-methyl, 4-ethyl, 4-propyl, 4-i-propyl, 4-butyl, 4-t-butyl, 4-i-butyl) were prepared and copolymerized with styrene. The ethylenes were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and octyl cyanoacetate, and characterized by CHN analysis, IR, 1H and 13C NMR. All the ethylenes were copolymerized with styrene in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis. Compositions of ST-OPCA copolymers ranged from 18.6 % to 27.4% of the OPCA monomer. This composition was calculated via nitrogen elemental analysis with alternating sequences of styrene. The order of relative reactivity (1/r1) with the radical end of the ST-polymer with OPCA was H (1.82) \u3e 4-buytl (1.80) \u3e 4-i-butyl (1.75) \u3e 4-t-butyl (1.61) \u3e 4-ethyl (1.46) \u3e 3-methyl (1.44) \u3e 4-methyl (1.31) \u3e 4-i-propyl (1.20) \u3e 2-methyl (1.1) and finally, 4-propyl (1.04).The copolymers were characterized by nitrogen analysis, IR, DSC and TGA. The thermal decomposition of the copolymers occurred in two steps: the first step between 200 °C to 400 °C with a slow decomposition from 400 °C to 800 °C and residue (1.8% to 6.5%)
The Addition Spectrum of a Lateral Dot from Coulomb and Spin Blockade Spectroscopy
Transport measurements are presented on a class of electrostatically defined
lateral dots within a high mobility two dimensional electron gas (2DEG). The
new design allows Coulomb Blockade(CB) measurements to be performed on a single
lateral dot containing 0, 1 to over 50 electrons. The CB measurements are
enhanced by the spin polarized injection from and into 2DEG magnetic edge
states. This combines the measurement of charge with the measurement of spin
through spin blockade spectroscopy. The results of Coulomb and spin blockade
spectroscopy for first 45 electrons enable us to construct the addition
spectrum of a lateral device. We also demonstrate that a lateral dot containing
a single electron is an effective local probe of a 2DEG edge.Comment: 4 pages, 4 figures submitted to Physical Review
The visibility study of S-T Landau-Zener-St\"uckelberg oscillations without applied initialization
Probabilities deduced from quantum information studies are usually based on
averaging many identical experiments separated by an initialization step. Such
initialization steps become experimentally more challenging to implement as the
complexity of quantum circuits increases. To better understand the consequences
of imperfect initialization on the deduced probabilities, we study the effect
of not initializing the system between measurements. For this we utilize
Landau-Zener-St\"uckelberg oscillations in a double quantum dot circuit.
Experimental results are successfully compared to theoretical simulations.Comment: 8 pages, 5 figure
Quantum noise limited and entanglement-assisted magnetometry
We study experimentally the fundamental limits of sensitivity of an atomic
radio-frequency magnetometer. First we apply an optimal sequence of state
preparation, evolution, and the back-action evading measurement to achieve a
nearly projection noise limited sensitivity. We furthermore experimentally
demonstrate that Einstein-Podolsky-Rosen (EPR) entanglement of atoms generated
by a measurement enhances the sensitivity to pulsed magnetic fields. We
demonstrate this quantum limited sensing in a magnetometer utilizing a truly
macroscopic ensemble of 1.5*10^12 atoms which allows us to achieve
sub-femtoTesla/sqrt(Hz) sensitivity.Comment: To appear in Physical Review Letters, April 9 issue (provisionally
Enhanced charge detection of spin qubit readout via an intermediate state
We employ an intermediate excited charge state of a lateral quantum dot
device to increase the charge detection contrast during the qubit state readout
procedure, allowing us to increase the visibility of coherent qubit
oscillations. This approach amplifies the coherent oscillation magnitude but
has no effect on the detector noise resulting in an increase in the signal to
noise ratio. In this letter we apply this scheme to demonstrate a significant
enhancement of the fringe contrast of coherent Landau-Zener-Stuckleberg
oscillations between singlet S and triplet T+ two-spin states.Comment: 3 pages, 3 figure
Non-linear exciton spin-splitting in single InAs/GaAs self-assembled quantum structures in ultrahigh magnetic fields
We report on the magnetic field dispersion of the exciton spin-splitting and
diamagnetic shift in single InAs/GaAs quantum dots (QDs) and dot molecules
(QDMs) up to = 28 T. Only for systems with strong geometric confinement,
the dispersions can be well described by simple field dependencies, while for
dots with weaker confinement considerable deviations are observed: most
importantly, in the high field limit the spin-splitting shows a non-linear
dependence on , clearly indicating light hole admixtures to the valence band
ground state
Optical readout of charge and spin in a self-assembled quantum dot in a strong magnetic field
We present a theory and experiment demonstrating optical readout of charge
and spin in a single InAs/GaAs self-assembled quantum dot. By applying a
magnetic field we create the filling factor 2 quantum Hall singlet phase of the
charged exciton. Increasing or decreasing the magnetic field leads to
electronic spin-flip transitions and increasing spin polarization. The
increasing total spin of electrons appears as a manifold of closely spaced
emission lines, while spin flips appear as discontinuities of emission lines.
The number of multiplets and discontinuities measures the number of carriers
and their spin. We present a complete analysis of the emission spectrum of a
single quantum dot with N=4 electrons and a single hole, calculated and
measured in magnetic fields up to 23 Tesla.Comment: 9 pages, 3 figures, submitted to Europhysics Letter
Experimental demonstration of entanglement-enhanced classical communication over a quantum channel with correlated noise
We present an experiment demonstrating entanglement-enhanced classical
communication capacity of a quantum channel with correlated noise. The channel
is modelled by a fiber optic link exhibiting random birefringence that
fluctuates on a time scale much longer than the temporal separation between
consecutive uses of the channel. In this setting, introducing entanglement
between two photons travelling down the fiber allows one to encode reliably up
to one bit of information into their joint polarization degree of freedom. When
no quantum correlations between two separate uses of the channel are allowed,
this capacity is reduced by a factor of more than three. We demonstrated this
effect using a fiber-coupled source of entagled photon pairs based on
spontaneous parametric down-conversion, and a linear-optics Bell state
measurement.Comment: 4 pages, 2 figures, REVTe
Exciton lifetime in InAs/GaAs quantum dot molecules
The exciton lifetimes in arrays of InAs/GaAs vertically coupled quantum
dot pairs have been measured by time-resolved photoluminescence. A considerable
reduction of by up to a factor of 2 has been observed as compared
to a quantum dots reference, reflecting the inter-dot coherence. Increase of
the molecular coupling strength leads to a systematic decrease of with
decreasing barrier width, as for wide barriers a fraction of structures shows
reduced coupling while for narrow barriers all molecules appear to be well
coupled. The coherent excitons in the molecules gain the oscillator strength of
the excitons in the two separate quantum dots halving the exciton lifetime.
This superradiance effect contributes to the previously observed increase of
the homogeneous exciton linewidth, but is weaker than the reduction of .
This shows that as compared to the quantum dots reference pure dephasing
becomes increasingly important for the molecules
Quantum phase estimation with lossy interferometers
We give a detailed discussion of optimal quantum states for optical two-mode
interferometry in the presence of photon losses. We derive analytical formulae
for the precision of phase estimation obtainable using quantum states of light
with a definite photon number and prove that maximization of the precision is a
convex optimization problem. The corresponding optimal precision, i.e. the
lowest possible uncertainty, is shown to beat the standard quantum limit thus
outperforming classical interferometry. Furthermore, we discuss more general
inputs: states with indefinite photon number and states with photons
distributed between distinguishable time bins. We prove that neither of these
is helpful in improving phase estimation precision.Comment: 12 pages, 5 figure
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