1,232 research outputs found
Fine structure and optical pumping of spins in individual semiconductor quantum dots
We review spin properties of semiconductor quantum dots and their effect on
optical spectra. Photoluminescence and other types of spectroscopy are used to
probe neutral and charged excitons in individual quantum dots with high
spectral and spatial resolution. Spectral fine structure and polarization
reveal how quantum dot spins interact with each other and with their
environment. By taking advantage of the selectivity of optical selection rules
and spin relaxation, optical spin pumping of the ground state electron and
nuclear spins is achieved. Through such mechanisms, light can be used to
process spins for use as a carrier of information
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
Giant nonlinearity and entanglement of single photons in photonic bandgap structures
Giantly enhanced cross-phase modulation with suppressed spectral broadening
is predicted between optically-induced dark-state polaritons whose propagation
is strongly affected by photonic bandgaps of spatially periodic media with
multilevel dopants. This mechanism is shown to be capable of fully entangling
two single-photon pulses with high fidelity.Comment: 7 pages, 1 figur
Non-local nuclear spin quieting in quantum dot molecules: Optically-induced extended two-electron spin coherence time
We demonstrate the extension of coherence between all four two-electron spin
ground states of an InAs quantum dot molecule (QDM) via non-local suppression
of nuclear spin fluctuations in both constituent quantum dots (QDs), while
optically addressing only the upper QD transitions. Long coherence times are
revealed through dark-state spectroscopy as resulting from nuclear spin locking
mediated by the exchange interaction between the QDs. Lineshape analysis
provides the first measurement of the quieting of the Overhauser field
distribution correlating with reduced nuclear spin fluctuations.Comment: Supplementary materials can be found on the publication page of our
website. http://research.physics.lsa.umich.edu/dst/Publications.htm
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
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
Internet cigarette vendors make tax-free claims and sell cigarettes cheaper than retail outlets: Table 1
This paper aims to (1) assess whether promotion of tax-free sales among Internet cigarette vendors (ICVs) changed between 2009 and 2011, (2) determine which types of ICVs are most likely to promote tax-free sales (e.g., US-based, international, or mixed location ICVs), and (3) compare the price of cigarettes advertised in ICVs to prices at brick-and-mortar retail outlets
Temperature dependence of polarization relaxation in semiconductor quantum dots
The decay time of the linear polarization degree of the luminescence in
strongly confined semiconductor quantum dots with asymmetrical shape is
calculated in the frame of second-order quasielastic interaction between
quantum dot charge carriers and LO phonons. The phonon bottleneck does not
prevent significantly the relaxation processes and the calculated decay times
can be of the order of a few tens picoseconds at temperature K,
consistent with recent experiments by Paillard et al. [Phys. Rev. Lett.
{\bf86}, 1634 (2001)].Comment: 4 pages, 4 figure
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