1,717 research outputs found
Fast initialization of the spin state of an electron in a quantum dot in the Voigt configuration
We consider the initialization of the spin-state of a single electron trapped
in a self-assembled quantum dot via optical pumping of a trion level. We show
that with a magnetic field applied perpendicular to the growth direction of the
dot, a near-unity fidelity can be obtained in a time equal to a few times the
inverse of the spin-conserving trion relaxation rate. This method is several
orders-of-magnitude faster than with the field aligned parallel, since this
configuration must rely on a slow hole spin-flip mechanism. This increase in
speed does result in a limit on the maximum obtainable fidelity, but we show
that for InAs dots, the error is very small.Comment: 4 pages, 4 figure
Fast spin rotations by optically controlled geometric phases in a quantum dot
We demonstrate optical control of the geometric phase acquired by one of the
spin states of an electron confined in a charge-tunable InAs quantum dot via
cyclic 2pi excitations of an optical transition in the dot. In the presence of
a constant in-plane magnetic field, these optically induced geometric phases
result in the effective rotation of the spin about the magnetic field axis and
manifest as phase shifts in the spin quantum beat signal generated by two
time-delayed circularly polarized optical pulses. The geometric phases
generated in this manner more generally perform the role of a spin phase gate,
proving potentially useful for quantum information applications.Comment: 4 pages, 3 figures, resubmitted to Physical Review Letter
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Test Score Reporting Referenced to Doubly-Moderated Cut Scores Using Splines
This study discusses and presents an example of a use of spline functions to establish and report test scores using a moderated system of any number of cut scores. Our main goals include studying the need for and establishing moderated standards and creating a reporting scale that is referenced to all the standards. Our secondary goals are to make possible straightforward interpretations about growth, and to report to users, scores that capitalize on their existing beliefs. Data from one state are used as an example to demonstrate how a complete system of cut scores might be developed and implemented. Accessed 6,255 times on https://pareonline.net from October 12, 2011 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right
All-Optical Ultrafast Control and Read-Out of a Single Negatively Charged Self-Assembled InAs Quantum Dot
We demonstrate the all-optical ultrafast manipulation and read-out of optical
transitions in a single negatively charged self-assembled InAs quantum dot, an
important step towards ultrafast control of the resident spin. Experiments
performed at zero magnetic field show the excitation and decay of the trion
(negatively charged exciton) as well as Rabi oscillations between the electron
and trion states. Application of a DC magnetic field perpendicular to the
growth axis of the dot enables observation of a complex quantum beat structure
produced by independent precession of the ground state electron and the excited
state heavy hole spins
Stimulated Raman spin coherence and spin-flip induced hole burning in charged GaAs quantum dots
High-resolution spectral hole burning (SHB) in coherent nondegenerate
differential transmission spectroscopy discloses spin-trion dynamics in an
ensemble of negatively charged quantum dots. In the Voigt geometry, stimulated
Raman spin coherence gives rise to Stokes and anti-Stokes sidebands on top of
the trion spectral hole. The prominent feature of an extremely narrow spike at
zero detuning arises from spin population pulsation dynamics. These SHB
features confirm coherent electron spin dynamics in charged dots, and the
linewidths reveal spin spectral diffusion processes.Comment: 5 pages, 5 figure
The inverse electromagnetic scattering problem in a piecewise homogeneous medium
This paper is concerned with the problem of scattering of time-harmonic
electromagnetic waves from an impenetrable obstacle in a piecewise homogeneous
medium. The well-posedness of the direct problem is established, employing the
integral equation method. Inspired by a novel idea developed by Hahner [11], we
prove that the penetrable interface between layers can be uniquely determined
from a knowledge of the electric far field pattern for incident plane waves.
Then, using the idea developed by Liu and Zhang [21], a new mixed reciprocity
relation is obtained and used to show that the impenetrable obstacle with its
physical property can also be recovered. Note that the wave numbers in the
corresponding medium may be different and therefore this work can be considered
as a generalization of the uniqueness result of [20].Comment: 19 pages, 2 figures, submitted for publicatio
Numerical simulation on detonation initiation and propagation in supersonic combustible mixtures with nonuniform species
Interaction induced decay of a heteronuclear two-atom system
Two-atom systems in small traps are of fundamental interest, first of all for
understanding the role of interactions in degenerate cold gases and for the
creation of quantum gates in quantum information processing with single-atom
traps. One of the key quantities is the inelastic relaxation (decay) time when
one of the atoms or both are in a higher hyperfine state. Here we measure this
quantity in a heteronuclear system of Rb and Rb in a micro
optical trap and demonstrate experimentally and theoretically the presence of
both fast and slow relaxation processes, depending on the choice of the initial
hyperfine states. The developed experimental method allows us to single out a
particular relaxation process and, in this sense, our experiment is a
"superclean platform" for collisional physics studies. Our results have also
implications for engineering of quantum states via controlled collisions and
creation of two-qubit quantum gates.Comment: 8 pages, 3 figure
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