234 research outputs found
Nonlinear optical absorption and dynamics in quantum wells
We present measurements of differential transmission and fourâwave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavyâhole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1â10 ÎŒs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electronâhole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on twoâphoton absorption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69941/2/APPLAB-61-11-1301-1.pd
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
High-resolution nonlinear laser spectroscopy of exciton relaxation in GaAs quantum wells
This paper describes measurements of exciton relaxation in GaAs/AlGaAs quantum well structures based on high resolution nonlinear laser spectroscopy. The nonlinear optical measurements show that low energy excitons can be localized by monolayer disorder of the quantum well interface. We show that these excitons migrate between localization sites by phonon assisted migration, leading to spectral diffusion of the excitons. The frequency domain measurements give a direct measure of the quasi-equilibrium exciton spectral redistribution due to exciton energy relaxation, and the temperature dependence of the measured migration rates confirms recent theoretical predictions. The observed line shapes are interpreted based on solutions we obtain to modified Bloch equations which include the effects of spectral diffusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47035/1/339_2004_Article_BF00331540.pd
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
Production of intense, coherent, tunable narrowâband lymanâalpha radiation
Nearly transform limited pulses of 1216 Ă
radiation have been generated by sum frequency generation in 0.1 to 10 torr of mercury vapor. The summed input beams, consisting of photons at 3127 Ă
and 5454 Ă
originate in 1 MHz bandâwidth ringâdye laser oscillators. The beams are amplified in pulsedâdye amplifiers pumped by the frequency doubled output of a Nd:YAG laser. The 3127 Ă
photons are tuned to be resonant with the twoâphoton 61S to 71S mercury transition. The VUV radiation can be tuned by varying the frequency of the third nonâresonant photon. We have also observed difference frequency generation at 2193 Ă
and intense fluorescence from the 61P state at 1849 Ă
. We have studied the intensity and linewidth dependence of the 1849 Ă
fluorescence and 1216 Ă
sum frequency signals on input beam intensity, mercury density, and buffer gas pressure and composition.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87716/2/49_1.pd
An electrically injected InAs/GaAs quantum-dot photonic crystal microcavity light-emitting diode
An electrically injected InAs/GaAs self-organized quantum-dot photonic crystal microcavity light-emitting diode operating at 1.04 ÎŒm is demonstrated. Lightâcurrent characteristics are obtained for devices with two- and five-defect period cavities with maximum light output of 0.17 ÎŒW measured in the surface-normal direction. Near-field images were also obtained for an injection current of 8.35 mA, showing light confinement within a few periods of the photonic crystal defect microcavity. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70407/2/APPLAB-81-20-3876-1.pd
Coherent nonlinear optical spectroscopy of single quantum dot excited states
We report a coherent nonlinear optical signature of the excited states of two quantum dots. By comparing the nonlinear spectra with the linear photoluminescence excitation spectrum, a clear identification of excited states is possible. © 2004 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70297/2/APPLAB-84-11-1928-1.pd
Measurement of relaxation between polarization eigenstates in single quantum dots
Low temperature relaxation of excitons between polarization eigenstates in single interface fluctuation quantum dots is studied using copolarized and cross-polarized transient differential transmission spectroscopy. The measured spin relaxation times are on the order of âŒ100 ps. Such a spin relaxation time is longer than the reported times for thin quantum wells, but considerably shorter than the predicted times for interface fluctuation quantum dots. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70166/2/APPLAB-81-22-4251-1.pd
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