43 research outputs found
Superbunching and Nonclassicality as new Hallmarks of Superradiance
Superradiance, i.e., spontaneous emission of coherent radiation by an
ensemble of identical two-level atoms in collective states introduced by Dicke
in 1954, is one of the enigmatic problems of quantum optics. The startling gist
is that even though the atoms have no dipole moment they radiate with increased
intensity in particular directions. Following the advances in our understanding
of superradiant emission by atoms in entangled states we examine the
quantum statistical properties of superradiance. Such investigations require
the system to have at least two excitations as one needs to explore the
photon-photon correlations of the radiation emitted by such states. We present
specifically results for the spatially resolved photon-photon correlations of
systems prepared in doubly excited states and give conditions when the
atomic system emits nonclassial light. Equally, we derive the conditions for
the occurrence of bunching and even of superbunching, a rare phenomenon
otherwise known only from nonclassical states of light like the squeezed
vacuum. We finally investigate the photon-photon cross correlations of the
spontaneously scattered light and highlight the nonclassicalty of such
correlations.Comment: 14 pages, 7 picture
Visibility of Young's interference fringes: Scattered light from small ion crystals
We observe interference in the light scattered from trapped Ca ion
crystals. By varying the intensity of the excitation laser, we study the
influence of elastic and inelastic scattering on the visibility of the fringe
pattern and discriminate its effect from that of the ion temperature and
wave-packet localization. In this way we determine the complex degree of
coherence and the mutual coherence of light fields produced by individual
atoms. We obtain interference fringes from crystals consisting of two, three
and four ions in a harmonic trap. Control of the trapping potential allows for
the adjustment of the interatomic distances and thus the formation of linear
arrays of atoms serving as a regular grating of microscopic scatterers.Comment: Main text: 5 pages, 4 figures. Supplemental Material: 2pages, 1
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Photon counting intensity interferometry in the blue at a 0.5 m telescope
Intensity interferometry is a re-emerging interferometry tool that alleviates
some of the challenges of amplitude interferometry at the cost of reduced
sensitivity. We demonstrate the feasibility of intensity interferometry with
fast single photon counting detectors at small telescopes by utilising a
telescope of diameter of merely \,m. The entire measurement setup,
including collimation, optical filtering, and two single photon detectors, is
attached directly to the telescope without the use of optical fibres,
facilitated by the large area of our single photon detectors. For digitisation
and timing, we utilise a Time-To-Amplitude-Converter. Observing Lyrae
(Vega) for a total exposure time of \,h over the course of six nights, an
auto-correlation signal with a contrast of and a
coherence time of ps at a SNR of 2.8 is measured. The result
fits well to preceding laboratory tests as well as expectations calculated from
the optical and electronic characteristics of our measurement setup. This
measurement, to our knowledge, constitutes the first time that a bunching
signal with starlight was measured in the B band with single photon counting
detectors. Simultaneously, this is to date the stellar intensity interferometry
measurement utilising the smallest telescope. Our successful measurement shows
that intensity interferometry can be adopted not only at large scale
facilities, but also at readily available and inexpensive smaller telescopes
Generation of N00N-like interferences with two thermal light sources
Measuring the th-order intensity correlation function of light emitted by
two statistically independent thermal light sources may display N00N-like
interferences of arbitrary order . We show that via a particular
choice of detector positions one can isolate -photon quantum paths where
either all photons are emitted from the same source or photons are
collectively emitted by both sources. The latter superposition displays
N00N-like oscillations with which may serve, e.g., in astronomy, for
imaging two distant thermal sources with -fold increased resolution. We
also discuss slightly modified detection schemes improving the visibility of
the N00N-like interference pattern and present measurements verifying the
theoretical predictions.Comment: 9 pages, 6 figure
Engineering of spontaneous emission in free space via conditional measurements
We study the collective spontaneous emission of three identical two-level
atoms initially prepared in the excited states by measuring Glauber's
third-order photon correlation function. Assuming two atoms at sub-wavelength
distance from each other such that they are subject to the dipole-dipole
interaction while the third one is located several wavelengths away, we observe
super- and subradiant decay alike, depending on the direction of observation.
Unlike the case where no remote atom is introduced or no conditional
measurements are performed, the spontaneous emission behavior of the
conditioned three-atom system differs strongly from the single-atom and the
canonical two-atom configuration. The conditional measurements associated with
the three-photon correlation function in combination with the dipole-dipole
interaction between the adjacent atoms lead to quantum interference among the
different decay channels allowing to engineer the spontaneous emission in space
and time