294 research outputs found
Generation of frequency sidebands on single photons with indistinguishability from quantum dots
Generation and manipulation of the quantum state of a single photon is at the
heart of many quantum information protocols. There has been growing interest in
using phase modulators as quantum optics devices that preserve coherence. In
this Letter, we have used an electro-optic phase modulator to shape the state
vector of single photons emitted by a quantum dot to generate new frequency
components (modes) and explicitly demonstrate that the phase modulation process
agrees with the theoretical prediction at a single photon level. Through
two-photon interference measurements we show that for an output consisting of
three modes (the original mode and two sidebands), the indistinguishability of
the mode engineered photon, measured through the secondorder intensity
correlation (g2(0)) is preserved. This work demonstrates a robust means to
generate a photonic qubit or more complex state (e.g., a qutrit) for quantum
communication applications by encoding information in the sidebands without the
loss of coherence
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
Stimulated and spontaneous optical generation of electron spin coherence in charged GaAs quantum dots
We report on the coherent optical excitation of electron spin polarization in
the ground state of charged GaAs quantum dots via an intermediate charged
exciton (trion) state. Coherent optical fields are used for the creation and
detection of the Raman spin coherence between the spin ground states of the
charged quantum dot. The measured spin decoherence time, which is likely
limited by the nature of the spin ensemble, approaches 10 ns at zero field. We
also show that the Raman spin coherence in the quantum beats is caused not only
by the usual stimulated Raman interaction but also by simultaneous spontaneous
radiative decay of either excited trion state to a coherent combination of the
two spin states.Comment: 4 pages, 3 figures. Minor modification
Creation of Entanglement between Two Electron Spins Induced by Many Spin Ensemble Excitations
We theoretically explore the possibility of creating spin entanglement by
simultaneously coupling two electronic spins to a nuclear ensemble. By
microscopically modeling the spin ensemble with a single mode boson field, we
use the time-dependent Fr\"{o}hlich transformation (TDFT) method developed most
recently [Yong Li, C. Bruder, and C. P. Sun, Phys. Rev. A \textbf{75}, 032302
(2007)] to calculate the effective coupling between the two spins. Our
investigation shows that the total system realizes a solid state based
architecture for cavity QED. Exchanging such kind effective boson in a virtual
process can result in an effective interaction between two spins. It is
discovered that a maximum entangled state can be obtained when the velocity of
the electrons matches the initial distance between them in a suitable way.
Moreover, we also study how the number of collective excitations influences the
entanglement. It is shown that the larger the number of excitation is, the less
the two spins entangle each other.Comment: 8 pages, 4 figure
Characteristic molecular properties of one-electron double quantum rings under magnetic fields
The molecular states of conduction electrons in laterally coupled quantum
rings are investigated theoretically. The states are shown to have a distinct
magnetic field dependence, which gives rise to periodic fluctuations of the
tunnel splitting and ring angular momentum in the vicinity of the ground state
crossings. The origin of these effects can be traced back to the Aharonov-Bohm
oscillations of the energy levels, along with the quantum mechanical tunneling
between the rings. We propose a setup using double quantum rings which shows
that Aharonov-Bohm effects can be observed even if the net magnetic flux
trapped by the carriers is zero.Comment: 16 pages (iopart format), 10 figures, accepted in J.Phys.Cond.Mat
Examining the influence of turbulence on viscosity measurements of molten germanium under reduced gravity
The thermophysical properties of liquid germanium were recently measured both in parabolic flight experiments and on the ISS in the ISS-EML facility. The viscosity measurements differed between the reduced gravity experiments and the literature values. Since the oscillating drop method has been widely used in EML, further exploration into this phenomenon was of interest. Models of the magnetohydrodynamic flow indicated that turbulence was present during the measurement in the ISS-EML facility, which accounts for the observed difference
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Demonstration of the Effect of Stirring on Nucleation from Experiments on the International Space Station Using the ISS-EML Facility
The effect of fluid flow on crystal nucleation in supercooled liquids is not well understood. The variable density and temperature gradients in the liquid make it difficult to study this under terrestrial gravity conditions. Nucleation experiments were therefore made in a microgravity environment using the Electromagnetic Levitation Facility on the International Space Station on a bulk glass-forming Zr57Cu15.4Ni12.6Al10Nb5 (Vit106), as well as Cu50Zr50 and the quasicrystal-forming Ti39.5Zr39.5Ni21 liquids. The maximum supercooling temperatures for each alloy were measured as a function of controlled stirring by applying various combinations of radio-frequency positioner and heater voltages to the water-cooled copper coils. The flow patterns were simulated from the known parameters for the coil and the levitated samples. The maximum nucleation temperatures increased systematically with increased fluid flow in the liquids for Vit106, but stayed nearly unchanged for the other two. These results are consistent with the predictions from the Coupled-Flux model for nucleation
Triplet-Singlet Spin Relaxation via Nuclei in a Double Quantum Dot
The spin of a confined electron, when oriented originally in some direction,
will lose memory of that orientation after some time. Physical mechanisms
leading to this relaxation of spin memory typically involve either coupling of
the electron spin to its orbital motion or to nuclear spins. Relaxation of
confined electron spin has been previously measured only for Zeeman or exchange
split spin states, where spin-orbit effects dominate relaxation, while spin
flips due to nuclei have been observed in optical spectroscopy studies. Using
an isolated GaAs double quantum dot defined by electrostatic gates and direct
time domain measurements, we investigate in detail spin relaxation for
arbitrary splitting of spin states. Results demonstrate that electron spin
flips are dominated by nuclear interactions and are slowed by several orders of
magnitude when a magnetic field of a few millitesla is applied. These results
have significant implications for spin-based information processing
Demonstration of the effect of stirring on nucleation from experiments on the International Space Station using the ISS-EML facility
The effect of fluid flow on crystal nucleation in supercooled liquids is not
well understood. The variable density and temperature gradients in the liquid
make it difficult to study this under terrestrial gravity conditions.
Nucleation experiments were therefore made in a microgravity environment using
the Electromagnetic Levitation facility on the International Space Station on a
bulk glass-forming Zr57Cu15.4Ni12.6Al10Nb5 (Vit106), as well as Cu50Zr50 and
the quasicrystal-forming Ti39.5Zr39.5Ni21 liquids. The maximum supercooling
temperatures for each alloy were measured as a function of controlled stirring
by applying various combinations of radio frequency positioner and heater
voltages to the water-cooled copper coils. The flow patterns were simulated
from the known parameters for the coil and the levitated samples. The maximum
nucleation temperatures increased systematically with increased fluid flow in
the liquids for Vit106, but stayed nearly unchanged for the other two. These
results are consistent with the predictions from the coupled-flux model for
nucleation.Comment: 21 pages, 2 figure
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