551 research outputs found
Pairwise entanglement and readout of atomic-ensemble and optical wave-packet modes in traveling-wave Raman interactions
We analyze quantum entanglement of Stokes light and atomic electronic
polarization excited during single-pass, linear-regime, stimulated Raman
scattering in terms of optical wave-packet modes and atomic-ensemble spatial
modes. The output of this process is confirmed to be decomposable into multiple
discrete, bosonic mode pairs, each pair undergoing independent evolution into a
two-mode squeezed state. For this we extend the Bloch-Messiah reduction
theorem, previously known for discrete linear systems (S. L. Braunstein, Phys.
Rev. A, vol. 71, 055801 (2005)). We present typical mode functions in the case
of one-dimensional scattering in an atomic vapor. We find that in the absence
of dispersion, one mode pair dominates the process, leading to a simple
interpretation of entanglement in this continuous-variable system. However,
many mode pairs are excited in the presence of dispersion-induced temporal
walkoff of the Stokes, as witnessed by the photon-count statistics. We also
consider the readout of the stored atomic polarization using the anti-Stokes
scattering process. We prove that the readout process can also be decomposed
into multiple mode pairs, each pair undergoing independent evolution analogous
to a beam-splitter transformation. We show that this process can have unit
efficiency under realistic experimental conditions. The shape of the output
light wave packet can be predicted. In case of unit readout efficiency it
contains only excitations originating from a specified atomic excitation mode
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
Minority Student Perceptions of Professional Pscyhology Application Packets: A Qualitative Study
This article reports the results of a qualitative study designed to determine issues salient in Black and Hispanic American students\u27 review and evaluation of program-application packets in professional psychology. The study served as an extension to the Yoshida et al. (1989) quantitative investigation. Students interested in pursuing doctoral studies in counseling or school psychology (N = 22) served as the sample. The qualitative methodology incorporated a think-aloud procedure and semistructured interviews. A theme analysis of transcribed interviews identified both major and minor themes central to participants\u27 evaluation of the packets. Major themes included financial aid, program requirements and course descriptions, demography of the student body, and the quality and clarity of application material. Specific suggestions on developing an application packet to send to inquiring prospective students are put forth. It is recommended that such a packet could serve as a costeffective minority-recruitment strategy
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
Theory of quantum frequency translation of light in optical fiber: application to interference of two photons of different color
We study quantum frequency translation and two-color photon interference
enabled by the Bragg scattering four-wave mixing process in optical fiber.
Using realistic model parameters, we computationally and analytically determine
the Green function and Schmidt modes for cases with various pump-pulse lengths.
These cases can be categorized as either "non-discriminatory" or
"discriminatory" in regards to their propensity to exhibit high-efficiency
translation or high-visibility two-photon interference for many different
shapes of input wave packets or for only a few input wave packets,
respectively. Also, for a particular case, the Schmidt mode set was found to be
nearly equal to a Hermite-Gaussian function set. The methods and results also
apply with little modification to frequency conversion by sum-frequency
conversion in optical crystals
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
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
The Bone-Vasculature Axis:Calcium Supplementation and the Role of Vitamin K
Calcium supplements are broadly prescribed to treat osteoporosis either as monotherapy or together with vitamin D to enhance calcium absorption. It is still unclear whether calcium supplementation significantly contributes to the reduction of bone fragility and fracture risk. Data suggest that supplementing post-menopausal women with high doses of calcium has a detrimental impact on cardiovascular morbidity and mortality. Chronic kidney disease (CKD) patients are prone to vascular calcification in part due to impaired phosphate excretion. Calcium-based phosphate binders further increase risk of vascular calcification progression. In both bone and vascular tissue, vitamin K-dependent processes play an important role in calcium homeostasis and it is tempting to speculate that vitamin K supplementation might protect from the potentially untoward effects of calcium supplementation. This review provides an update on current literature on calcium supplementation among post-menopausal women and CKD patients and discusses underlying molecular mechanisms of vascular calcification. We propose therapeutic strategies with vitamin K2 treatment to prevent or hold progression of vascular calcification as a consequence of excessive calcium intake
Bipolar spin blockade and coherent state superpositions in a triple quantum dot
Spin qubits based on interacting spins in double quantum dots have been
successfully demonstrated. Readout of the qubit state involves a conversion of
spin to charge information, universally achieved by taking advantage of a spin
blockade phenomenon resulting from Pauli's exclusion principle. The archetypal
spin blockade transport signature in double quantum dots takes the form of a
rectified current. Currently more complex spin qubit circuits including triple
quantum dots are being developed. Here we show both experimentally and
theoretically (a) that in a linear triple quantum dot circuit, the spin
blockade becomes bipolar with current strongly suppressed in both bias
directions and (b) that a new quantum coherent mechanism becomes relevant.
Within this mechanism charge is transferred non-intuitively via coherent states
from one end of the linear triple dot circuit to the other without involving
the centre site. Our results have implications in future complex
nano-spintronic circuits.Comment: 21 pages, 7 figure
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