909 research outputs found
Climbing the Jaynes-Cummings Ladder and Observing its Sqrt(n) Nonlinearity in a Cavity QED System
The already very active field of cavity quantum electrodynamics (QED),
traditionally studied in atomic systems, has recently gained additional
momentum by the advent of experiments with semiconducting and superconducting
systems. In these solid state implementations, novel quantum optics experiments
are enabled by the possibility to engineer many of the characteristic
parameters at will. In cavity QED, the observation of the vacuum Rabi mode
splitting is a hallmark experiment aimed at probing the nature of matter-light
interaction on the level of a single quantum. However, this effect can, at
least in principle, be explained classically as the normal mode splitting of
two coupled linear oscillators. It has been suggested that an observation of
the scaling of the resonant atom-photon coupling strength in the
Jaynes-Cummings energy ladder with the square root of photon number n is
sufficient to prove that the system is quantum mechanical in nature. Here we
report a direct spectroscopic observation of this characteristic quantum
nonlinearity. Measuring the photonic degree of freedom of the coupled system,
our measurements provide unambiguous, long sought for spectroscopic evidence
for the quantum nature of the resonant atom-field interaction in cavity QED. We
explore atom-photon superposition states involving up to two photons, using a
spectroscopic pump and probe technique. The experiments have been performed in
a circuit QED setup, in which ultra strong coupling is realized by the large
dipole coupling strength and the long coherence time of a superconducting qubit
embedded in a high quality on-chip microwave cavity.Comment: ArXiv version of manuscript published in Nature in July 2008, 5
pages, 5 figures, hi-res version at
http://www.finkjohannes.com/SqrtNArxivPreprint.pd
Quadrature squeezed photons from a two-level system.
Resonance fluorescence arises from the interaction of an optical field with a two-level system, and has played a fundamental role in the development of quantum optics and its applications. Despite its conceptual simplicity, it entails a wide range of intriguing phenomena, such as the Mollow-triplet emission spectrum, photon antibunching and coherent photon emission. One fundamental aspect of resonance fluorescence--squeezing in the form of reduced quantum fluctuations in the single photon stream from an atom in free space--was predicted more than 30 years ago. However, the requirement to operate in the weak excitation regime, together with the combination of modest oscillator strength of atoms and low collection efficiencies, has continued to necessitate stringent experimental conditions for the observation of squeezing with atoms. Attempts to circumvent these issues had to sacrifice antibunching, owing to either stimulated forward scattering from atomic ensembles or multi-photon transitions inside optical cavities. Here, we use an artificial atom with a large optical dipole enabling 100-fold improvement of the photon detection rate over the natural atom counterpart and reach the necessary conditions for the observation of quadrature squeezing in single resonance-fluorescence photons. By implementing phase-dependent homodyne intensity-correlation detection, we demonstrate that the electric field quadrature variance of resonance fluorescence is three per cent below the fundamental limit set by vacuum fluctuations, while the photon statistics remain antibunched. The presence of squeezing and antibunching simultaneously is a fully non-classical outcome of the wave-particle duality of photons.We acknowledge financial support from the University of Cambridge, the European Research Council ERC Consolidator Grant Agreement No. 617985 and the EU-FP7 Marie Curie Initial Training Network S3NANO. C.M. acknowledges Clare College Cambridge for financial support through a Junior Research Fellowship.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1486
A semiconductor source of triggered entangled photon pairs?
The realisation of a triggered entangled photon source will be of great
importance in quantum information, including for quantum key distribution and
quantum computation. We show here that: 1) the source reported in ``A
semiconductor source of triggered entangled photon pairs''[1. Stevenson et al.,
Nature 439, 179 (2006)]} is not entangled; 2) the entanglement indicators used
in Ref. 1 are inappropriate, relying on assumptions invalidated by their own
data; and 3) even after simulating subtraction of the significant quantity of
background noise, their source has insignificant entanglement.Comment: 5 pages in pre-print format, 1 tabl
Circuit Quantum Electrodynamics: Coherent Coupling of a Single Photon to a Cooper Pair Box
Under appropriate conditions, superconducting electronic circuits behave
quantum mechanically, with properties that can be designed and controlled at
will. We have realized an experiment in which a superconducting two-level
system, playing the role of an artificial atom, is strongly coupled to a single
photon stored in an on-chip cavity. We show that the atom-photon coupling in
this circuit can be made strong enough for coherent effects to dominate over
dissipation, even in a solid state environment. This new regime of matter light
interaction in a circuit can be exploited for quantum information processing
and quantum communication. It may also lead to new approaches for single photon
generation and detection.Comment: 8 pages, 4 figures, accepted for publication in Nature, embargo does
apply, version with high resolution figures available at:
http://www.eng.yale.edu/rslab/Andreas/content/science/PubsPapers.htm
Resolving photon number states in a superconducting circuit
Electromagnetic signals are always composed of photons, though in the circuit
domain those signals are carried as voltages and currents on wires, and the
discreteness of the photon's energy is usually not evident. However, by
coupling a superconducting qubit to signals on a microwave transmission line,
it is possible to construct an integrated circuit where the presence or absence
of even a single photon can have a dramatic effect. This system is called
circuit quantum electrodynamics (QED) because it is the circuit equivalent of
the atom-photon interaction in cavity QED. Previously, circuit QED devices were
shown to reach the resonant strong coupling regime, where a single qubit can
absorb and re-emit a single photon many times. Here, we report a circuit QED
experiment which achieves the strong dispersive limit, a new regime of cavity
QED in which a single photon has a large effect on the qubit or atom without
ever being absorbed. The hallmark of this strong dispersive regime is that the
qubit transition can be resolved into a separate spectral line for each photon
number state of the microwave field. The strength of each line is a measure of
the probability to find the corresponding photon number in the cavity. This
effect has been used to distinguish between coherent and thermal fields and
could be used to create a photon statistics analyzer. Since no photons are
absorbed by this process, one should be able to generate non-classical states
of light by measurement and perform qubit-photon conditional logic, the basis
of a logic bus for a quantum computer.Comment: 6 pages, 4 figures, hi-res version at
http://www.eng.yale.edu/rslab/papers/numbersplitting_hires.pd
Staphylococcus aureus internalisation enhances bacterial survival through modulation of host immune responses and mast cell activation
FishNet: an online database of zebrafish anatomy
Background: Over the last two decades, zebrafish have been established as a genetically versatile model system for investigating many different aspects of vertebrate developmental biology. With the credentials of zebrafish as a developmental model now well recognized, the emerging new opportunity is the wider application of zebrafish biology to aspects of human disease modelling. This rapidly increasing use of zebrafish as a model for human disease has necessarily generated interest in the anatomy of later developmental phases such as the larval, juvenile, and adult stages, during which many of the key aspects of organ morphogenesis and maturation take place. Anatomical resources and references that encompass these stages are non-existent in zebrafish and there is therefore an urgent need to understand how different organ systems and anatomical structures develop throughout the life of the fish. Results: To overcome this deficit we have utilized the technique of optical projection tomography to produce three-dimensional (3D) models of larval fish. In order to view and display these models we have created FishNet http://www.fishnet.org.au, an interactive reference of zebrafish anatomy spanning the range of zebrafish development from 24 h until adulthood. Conclusion: FishNet contains more than 36 000 images of larval zebrafish, with more than 1 500 of these being annotated. The 3D models can be manipulated on screen or virtually sectioned. This resource represents the first complete embryo to adult atlas for any species in 3D
Molecular identification of adenovirus causing respiratory tract infection in pediatric patients at the University of Malaya Medical Center
<p>Abstract</p> <p>Background</p> <p>There are at least 51 adenovirus serotypes (AdV) known to cause human infections. The prevalence of the different human AdV (HAdV) serotypes varies among different regions. Presently, there are no reports of the prevalent HAdV types found in Malaysia. The present study was undertaken to identify the HAdV types associated primarily with respiratory tract infections (RTI) of young children in Malaysia.</p> <p>Methods</p> <p>Archived HAdV isolates from pediatric patients with RTI seen at the University of Malaya Medical Center (UMMC), Kuala Lumpur, Malaysia from 1999 to 2005 were used. Virus isolates were inoculated into cell culture and DNA was extracted when cells showed significant cytopathic effects. AdV partial hexon gene was amplified and the sequences together with other known HAdV hexon gene sequences were used to build phylogenetic trees. Identification of HAdV types found among young children in Malaysia was inferred from the phylograms.</p> <p>Results</p> <p>At least 2,583 pediatric patients with RTI sought consultation and treatment at the UMMC from 1999 to 2005. Among these patients, 48 (< 2%) were positive for HAdV infections. Twenty-seven isolates were recovered and used for the present study. Nineteen of the 27 (~70%) isolates belonged to HAdV species C (HAdV-C) and six (~22%) were of HAdV species B (HAdV-B). Among the HAdV-C species, 14 (~74%) of them were identified as HAdV type 1 (HAdV-1) and HAdV type 2 (HAdV-2), and among the HAdV-B species, HAdV type 3 (HAdV-3) was the most common serotype identified. HAdV-C species also was isolated from throat and rectal swabs of children with hand, foot, and mouth disease (HFMD). Two isolates were identified as corresponding to HAdV-F species from a child with HFMD and a patient with intestinal obstruction.</p> <p>Conclusions</p> <p>HAdV-1 and HAdV-2 were the most common HAdV isolated from pediatric patients who sought treatment for RTI at the UMMC from 1999 to 2005. HAdV-B, mainly HAdV-3, was recovered from ~22% of the patients. These findings provide a benchmark for future studies on the prevalence and epidemiology of HAdV types in Malaysia and in the region.</p
Supranuclear eye movements and nystagmus in children: A review of the literature and guide to clinical examination, interpretation of findings and age-appropriate norms.
Abnormal eye movements in children present a significant challenge to Ophthalmologists and other healthcare professionals. Similarly, examination of supra-nuclear eye movements in children and interpretation of any resulting clinical signs can seem very complex. A structured assessment is often lacking although in many cases, simple clinical observations, combined with a basic understanding of the underlying neurology, can hold the key to clinical diagnosis. As the range of underlying diagnoses for children with abnormal eye movements is broad, recognising clinical patterns and understanding their neurological basis is also imperative for ongoing management. Here we present a review and best practice guide for a structured, methodical clinical examination of supranuclear eye movements in children, a guide to clinical interpretation and age-appropriate norms. We also detail the more common specific clinical findings and how they should be interpreted and used to guide further management. In summary, this review will encourage clinicians to combine a structured assessment and a logical interpretation of the resulting clinical signs, in order to recognise patterns of presentation and avoid unnecessary investigations and protracted delays in diagnosis and clinical care
Subcycle Quantum Electrodynamics
Besides their stunning physical properties which are unmatched in a classical
world, squeezed states of electromagnetic radiation bear advanced application
potentials in quantum information systems and precision metrology, including
gravitational wave detectors with unprecedented sensitivity. Since the first
experiments on such nonclassical light, quantum analysis has been based on
homodyning techniques and photon correlation measurements. These methods
require a well-defined carrier frequency and photons contained in a quantum
state need to be absorbed or amplified. They currently function in the visible
to near-infrared and microwave spectral ranges. Quantum nondemolition
experiments may be performed at the expense of excess fluctuations in another
quadrature. Here we generate mid-infrared time-locked patterns of squeezed
vacuum noise. After propagation through free space, the quantum fluctuations of
the electric field are studied in the time domain by electro-optic sampling
with few-femtosecond laser pulses. We directly compare the local noise
amplitude to the level of bare vacuum fluctuations. This nonlinear approach
operates off resonance without absorption or amplification of the field that is
investigated. Subcycle intervals with noise level significantly below the pure
quantum vacuum are found. Enhanced fluctuations in adjacent time segments
manifest generation of highly correlated quantum radiation as a consequence of
the uncertainty principle. Together with efforts in the far infrared, this work
opens a window to the elementary quantum dynamics of light and matter in an
energy range at the boundary between vacuum and thermal background conditions.Comment: 19 pages, 4 figure
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