790 research outputs found
Squeezing spectra from s-ordered quasiprobability distributions. Application to dispersive optical bistability
It is well known that the squeezing spectrum of the field exiting a nonlinear
cavity can be directly obtained from the fluctuation spectrum of normally
ordered products of creation and annihilation operators of the cavity mode. In
this article we show that the output field squeezing spectrum can be derived
also by combining the fluctuation spectra of any pair of s-ordered products of
creation and annihilation operators. The interesting result is that the
spectrum obtained in this way from the linearized Langevin equations is exact,
and this occurs in spite of the fact that no s-ordered quasiprobability
distribution verifies a true Fokker-Planck equation, i.e., the Langevin
equations used for deriving the squeezing spectrum are not exact. The
(linearized) intracavity squeezing obtained from any s-ordered distribution is
also exact. These results are exemplified in the problem of dispersive optical
bistability.Comment: 15 pages, no figures, to be published in Journal of Modern Optic
Observation of squeezed light from one atom excited with two photons
Single quantum emitters like atoms are well-known as non-classical light
sources which can produce photons one by one at given times, with reduced
intensity noise. However, the light field emitted by a single atom can exhibit
much richer dynamics. A prominent example is the predicted ability for a single
atom to produce quadrature-squeezed light, with sub-shot-noise amplitude or
phase fluctuations. It has long been foreseen, though, that such squeezing
would be "at least an order of magnitude more difficult" to observe than the
emission of single photons. Squeezed beams have been generated using
macroscopic and mesoscopic media down to a few tens of atoms, but despite
experimental efforts, single-atom squeezing has so far escaped observation.
Here we generate squeezed light with a single atom in a high-finesse optical
resonator. The strong coupling of the atom to the cavity field induces a
genuine quantum mechanical nonlinearity, several orders of magnitude larger
than for usual macroscopic media. This produces observable quadrature squeezing
with an excitation beam containing on average only two photons per system
lifetime. In sharp contrast to the emission of single photons, the squeezed
light stems from the quantum coherence of photon pairs emitted from the system.
The ability of a single atom to induce strong coherent interactions between
propagating photons opens up new perspectives for photonic quantum logic with
single emittersComment: Main paper (4 pages, 3 figures) + Supplementary information (5 pages,
2 figures). Revised versio
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
Measurements of the Correlation Function of a Microwave Frequency Single Photon Source
At optical frequencies the radiation produced by a source, such as a laser, a
black body or a single photon source, is frequently characterized by analyzing
the temporal correlations of emitted photons using single photon counters. At
microwave frequencies, however, there are no efficient single photon counters
yet. Instead, well developed linear amplifiers allow for efficient measurement
of the amplitude of an electromagnetic field. Here, we demonstrate how the
properties of a microwave single photon source can be characterized using
correlation measurements of the emitted radiation with such detectors. We also
demonstrate the cooling of a thermal field stored in a cavity, an effect which
we detect using a cross-correlation measurement of the radiation emitted at the
two ends of the cavity.Comment: 5 pages, 4 figure
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
Age-specific trends in cardiovascular mortality rates in the Netherlands between 1980 and 2009
Recent analyses suggest the decline in coronary heart disease mortality rates is slowing in younger age groups in countries such as the US and the UK. This work aimed to analyse recent trends in cardiovascular mortality rates in the Netherlands. Analysis was of annual all circulatory, ischaemic heart disease (IHD), and cerebrovascular disease mortality rates between 1980 and 2009 for the Netherlands. Data were stratified by sex and 10-year age group (age 35–85+). The annual rate of change and significant changes in the trend were identified using joinpoint Poisson regression. For almost all age and sex groups examined the rate of IHD and cerebrovascular disease mortality in the Netherlands has more than halved between 1980 and 2009. The decline in mortality from both IHD and cerebrovascular disease is continuing for all ages and sex groups, with anacceleration in the decline apparent from the late 1990s/early 2000s. The decline in age-specific all circulatory, coronary heart disease and cerebrovascular disease mortality rates continues for all age and sex groups in the Netherlands
Cavity Induced Interfacing of Atoms and Light
This chapter introduces cavity-based light-matter quantum interfaces, with a
single atom or ion in strong coupling to a high-finesse optical cavity. We
discuss the deterministic generation of indistinguishable single photons from
these systems; the atom-photon entanglement intractably linked to this process;
and the information encoding using spatio-temporal modes within these photons.
Furthermore, we show how to establish a time-reversal of the aforementioned
emission process to use a coupled atom-cavity system as a quantum memory. Along
the line, we also discuss the performance and characterisation of cavity
photons in elementary linear-optics arrangements with single beam splitters for
quantum-homodyne measurements.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond
We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the models and the methods of treatment of such systems, we discuss in detail,
which challenges of condensed matter physics can be addressed with (i)
disordered ultracold lattice gases, (ii) frustrated ultracold gases, (iii)
spinor lattice gases, (iv) lattice gases in "artificial" magnetic fields, and,
last but not least, (v) quantum information processing in lattice gases. For
completeness, also some recent progress related to the above topics with
trapped cold gases will be discussed.Comment: Review article. v2: published version, 135 pages, 34 figure
Kiwi Forego Vision in the Guidance of Their Nocturnal Activities
BACKGROUND: In vision, there is a trade-off between sensitivity and resolution, and any eye which maximises information gain at low light levels needs to be large. This imposes exacting constraints upon vision in nocturnal flying birds. Eyes are essentially heavy, fluid-filled chambers, and in flying birds their increased size is countered by selection for both reduced body mass and the distribution of mass towards the body core. Freed from these mass constraints, it would be predicted that in flightless birds nocturnality should favour the evolution of large eyes and reliance upon visual cues for the guidance of activity. METHODOLOGY/PRINCIPAL FINDINGS: We show that in Kiwi (Apterygidae), flightlessness and nocturnality have, in fact, resulted in the opposite outcome. Kiwi show minimal reliance upon vision indicated by eye structure, visual field topography, and brain structures, and increased reliance upon tactile and olfactory information. CONCLUSIONS/SIGNIFICANCE: This lack of reliance upon vision and increased reliance upon tactile and olfactory information in Kiwi is markedly similar to the situation in nocturnal mammals that exploit the forest floor. That Kiwi and mammals evolved to exploit these habitats quite independently provides evidence for convergent evolution in their sensory capacities that are tuned to a common set of perceptual challenges found in forest floor habitats at night and which cannot be met by the vertebrate visual system. We propose that the Kiwi visual system has undergone adaptive regressive evolution driven by the trade-off between the relatively low rate of gain of visual information that is possible at low light levels, and the metabolic costs of extracting that information
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