179 research outputs found
Quantum dot spectroscopy using cavity QED
Cavity quantum electrodynamics has attracted substantial interest, both due
to its potential role in the field of quantum information processing and as a
testbed for basic experiments in quantum mechanics. Here, we show how cavity
quantum electrodynamics using a tunable photonic crystal nanocavity in the
strong coupling regime can be used for single quantum dot spectroscopy. From
the distinctive avoided crossings observed in the strongly coupled system we
can identify the neutral and single positively charged exciton as well as the
biexciton transitions. Moreover we are able to investigate the fine structure
of those transitions and to identify a novel cavity mediated mixing of bright
and dark exciton states, where the hyperfine interactions with lattice nuclei
presumably play a key role. These results are enabled by a deterministic
coupling scheme which allowed us to achieve unprecedented coupling strengths in
excess of 0.15 meV.Comment: 5 pages, 3 figure
Optomechanics in an ultrahigh-Q two-dimensional photonic crystal cavity
We demonstrate an ultrahigh-Q slotted two-dimensional photonic crystal cavity capable of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The measured optical quality factor is Q = 1.2×10^6 for a cavity with an effective modal volume of V_(eff) = 0.04(λ)^3. Optical transduction of the thermal motion of the fundamental in-plane mechanical resonance of the structure (ν_m = 151 MHz) is performed, from which a zero-point motion optomechanical coupling rate of g∗/2π = 320 kHz is inferred. Dynamical back-action of the optical field on the mechanical motion, resulting in cooling and amplication of the mechanical motion, is also demonstrated
Photon Antibunching in the Photoluminescence Spectra of a Single Carbon Nanotube
We report the first observation of photon antibunching in the
photoluminescence from single carbon nanotubes. The emergence of a fast
luminescence decay component under strong optical excitation indicates that
Auger processes are partially responsible for inhibiting two-photon generation.
Additionally, the presence of exciton localization at low temperatures ensures
that nanotubes emit photons predominantly one by one. The fact that multiphoton
emission probability can be smaller than 5% suggests that carbon nanotubes
could be used as a source of single photons for applications in quantum
cryptography.Comment: content as publishe
Resolution of the mystery of counter-intuitive photon correlations in far off-resonance emission from a quantum dot-cavity system
Cavity quantum-electrodynamics experiments using an atom coupled to a single
radiation-field mode have played a central role in testing foundations of
quantum mechanics, thus motivating solid-state implementations using single
quantum dots coupled to monolithic nano-cavities. In stark contrast to their
atom based counterparts, the latter experiments revealed strong cavity
emission, even when the quantum dot is far off resonance. Here we present
experimental and theoretical results demonstrating that this effect arises from
the mesoscopic nature of quantum dot confinement, ensuring the presence of a
quasi-continuum of transitions between excited quantum dot states that are
enhanced by the cavity mode. Our model fully explains photon correlation
measurements demonstrating that photons emitted at the cavity frequency are
essentially uncorrelated with each other even though they are generated by a
single quantum dot.Comment: 5 pages, 4 figure
Benzodiazepine dependence studies in animals: An overview
A selective review of benzodiazepine dependence studies in animals is presented, emphasizing areas of drug self-injection, drug discrimination, and physiological dependence. Benzodiazepines as a class, as well as long-acting barbiturates, appear to maintain drug self-injection behavior less well than ultrashort-acting barbiturates. The duration of action as well as the rapidity of onset of these drugs may be important determinants of their reinforcing efficacy. Drug discrimination procedures may allow evaluation of the relative rapidity at onset and duration of action of these drugs to evaluate this and related hypotheses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50212/1/430010712_ftp.pd
Strongly correlated photons on a chip
Optical non-linearities at the single-photon level are key ingredients for
future photonic quantum technologies. Prime candidates for the realization of
strong photon-photon interactions necessary for implementing quantum
information processing tasks as well as for studying strongly correlated
photons in an integrated photonic device setting are quantum dots embedded in
photonic crystal nanocavities. Here, we report strong quantum correlations
between photons on picosecond timescales. We observe (a) photon antibunching
upon resonant excitation of the lowest-energy polariton state, proving that the
first cavity photon blocks the subsequent injection events, and (b) photon
bunching when the laser field is in two-photon resonance with the polariton
eigenstates of the second Jaynes-Cummings manifold, demonstrating that two
photons at this color are more likely to be injected into the cavity jointly,
than they would otherwise. Together,these results demonstrate unprecedented
strong single-photon non-linearities, paving the way for realizing a
single-photon transistor or a quantum optical Josephson interferometer
A microchip optomechanical accelerometer
The monitoring of accelerations is essential for a variety of applications
ranging from inertial navigation to consumer electronics. The basic operation
principle of an accelerometer is to measure the displacement of a flexibly
mounted test mass; sensitive displacement measurement can be realized using
capacitive, piezo-electric, tunnel-current, or optical methods. While optical
readout provides superior displacement resolution and resilience to
electromagnetic interference, current optical accelerometers either do not
allow for chip-scale integration or require bulky test masses. Here we
demonstrate an optomechanical accelerometer that employs ultra-sensitive
all-optical displacement read-out using a planar photonic crystal cavity
monolithically integrated with a nano-tethered test mass of high mechanical
Q-factor. This device architecture allows for full on-chip integration and
achieves a broadband acceleration resolution of 10 \mu g/rt-Hz, a bandwidth
greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical
power requirements. Moreover, the nano-gram test masses used here allow for
optomechanical back-action in the form of cooling or the optical spring effect,
setting the stage for a new class of motional sensors.Comment: 16 pages, 9 figure
Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015
The third International Exercise-Associated Hyponatremia (EAH) Consensus Development Conference convened in Carlsbad, California in February 2015 with a panel of 17 international experts. The delegates represented 4 countries and 9 medical and scientific sub-specialties pertaining to athletic training, exercise physiology, sports medicine, water/sodium metabolism, and body fluid homeostasis. The primary goal of the panel was to review the existing data on EAH and update the 2008 Consensus Statement.1 This document serves to replace the second International EAH Consensus Development Conference Statement and launch an educational campaign designed to address the morbidity and mortality associated with a preventable and treatable fluid imbalance.
The following statement is a summary of the data synthesized by the 2015 EAH Consensus Panel and represents an evolution of the most current knowledge on EAH. This document will summarize the most current information on the prevalence, etiology, diagnosis, treatment and prevention of EAH for medical personnel, athletes, athletic trainers, and the greater public. The EAH Consensus Panel strove to clearly articulate what we agreed upon, did not agree upon, and did not know, including minority viewpoints that were supported by clinical experience and experimental data. Further updates will be necessary to both: (1) remain current with our understanding and (2) critically assess the effectiveness of our present recommendations. Suggestions for future research and educational strategies to reduce the incidence and prevalence of EAH are provided at the end of the document as well as areas of controversy that remain in this topic. [excerpt
Identification of Residues in the Heme Domain of Soluble Guanylyl Cyclase that are Important for Basal and Stimulated Catalytic Activity
Nitric oxide signals through activation of soluble guanylyl cyclase (sGC), a heme-containing heterodimer. NO binds to the heme domain located in the N-terminal part of the β subunit of sGC resulting in increased production of cGMP in the catalytic domain located at the C-terminal part of sGC. Little is known about the mechanism by which the NO signaling is propagated from the receptor domain (heme domain) to the effector domain (catalytic domain), in particular events subsequent to the breakage of the bond between the heme iron and Histidine 105 (H105) of the β subunit. Our modeling of the heme-binding domain as well as previous homologous heme domain structures in different states point to two regions that could be critical for propagation of the NO activation signal. Structure-based mutational analysis of these regions revealed that residues T110 and R116 in the αF helix-β1 strand, and residues I41 and R40 in the αB-αC loop mediate propagation of activation between the heme domain and the catalytic domain. Biochemical analysis of these heme mutants allows refinement of the map of the residues that are critical for heme stability and propagation of the NO/YC-1 activation signal in sGC
Novel Binding Mode of a Potent and Selective Tankyrase Inhibitor
Tankyrases (TNKS1 and TNKS2) are key regulators of cellular processes such as telomere pathway and Wnt signaling. IWRs (inhibitors of Wnt response) have recently been identified as potent and selective inhibitors of tankyrases. However, it is not clear how these IWRs interact with tankyrases. Here we report the crystal structure of the catalytic domain of human TNKS1 in complex with IWR2, which reveals a novel binding site for tankyrase inhibitors. The TNKS1/IWR2 complex provides a molecular basis for their strong and specific interactions and suggests clues for further development of tankyrase inhibitors
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