513 research outputs found
Superabsorption of light via quantum engineering
Almost 60 years ago Dicke introduced the term superradiance to describe a
signature quantum effect: N atoms can collectively emit light at a rate
proportional to N^2. Even for moderate N this represents a significant increase
over the prediction of classical physics, and the effect has found applications
ranging from probing exciton delocalisation in biological systems, to
developing a new class of laser, and even in astrophysics. Structures that
super-radiate must also have enhanced absorption, but the former always
dominates in natural systems. Here we show that modern quantum control
techniques can overcome this restriction. Our theory establishes that
superabsorption can be achieved and sustained in certain simple nanostructures,
by trapping the system in a highly excited state while extracting energy into a
non-radiative channel. The effect offers the prospect of a new class of quantum
nanotechnology, capable of absorbing light many times faster than is currently
possible; potential applications of this effect include light harvesting and
photon detection. An array of quantum dots or a porphyrin ring could provide an
implementation to demonstrate this effect
Aharonov-Bohm interference as a probe of Majorana fermions
Majorana fermions act as their own antiparticle, and they have long been
thought to be confined to the realm of pure theory. However, interest in them
has recently resurfaced, as it was realized through the work of Kitaev that
some experimentally accessible condensed matter systems can host these exotic
excitations as bound states on the boundaries of 1D chains, and that their
topological and non-abelian nature holds promise for quantum computation.
Unambiguously detecting the experimental signatures of Majorana bound states
has turned out to be challenging, as many other phenomena lead to similar
experimental behaviour. Here, we computationally study a ring comprised of two
Kitaev model chains with tunnel coupling between them, where an applied
magnetic field allows for Aharonov-Bohm interference in transport through the
resulting ring structure. We use a non-equilibrium Green's function technique
to analyse the transport properties of the ring in both the presence and
absence of Majorana zero modes. This computational model suggests another
signature for the presence of these topologically protected bound states can be
found in the magnetic field dependence of devices with loop geometries.Comment: 9 pages, 9 figure
Molecular footprints of the Holocene retreat of dwarf birch in Britain
© 2014 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited
Pulse-induced acoustoelectric vibrations in surface-gated GaAs-based quantum devices
We present the results of a numerical investigation which show the excitation
of acoustoelectric modes of vibration in GaAs-based heterostructures due to
sharp nano-second electric-field pulses applied across surface gates. In
particular, we show that the pulses applied in quantum information processing
applications are capable of exciting acoustoelectric modes of vibration
including surface acoustic modes which propagate for distances greater than
conventional device dimensions. We show that the pulse-induced acoustoelectric
vibrations are capable of inducing significant undesired perturbations to the
evolution of quantum systems.Comment: To be published in Phys. Rev.
Life history evolution, species differences and phenotypic plasticity in hemiparasitic eyebrights (Euphrasia)
Premise of the study: Species delimitation in parasitic organisms is challenging as traits used in the identification of species are often plastic and vary depending on the host. Here, we use species from a recent radiation of generalist hemiparasitic Euphrasia to investigate trait variation and trait plasticity. We test whether Euphrasia species show reliable trait differences, investigate whether these differences correspond to life history trade-offs between growth and reproduction, and quantify plasticity in response to host species.
Methods: We perform common garden experiments to evaluate trait differences between eleven Euphrasia taxa grown on a common host, document phenotypic plasticity when a single Euphrasia species is grown on eight different hosts, and relate our observations to trait differences recorded in the wild.
Key results: Euphrasia exhibit variation in life history strategies; some individuals transition rapidly to flower at the expense of early season growth, while others invest in vegetative growth and delay flowering. Life history differences are present between some species, though many related taxa lack clear-cut trait differences. Species differences are further blurred by phenotypic plasticity—many traits are plastic and change with host type or between environments.
Conclusions: Phenotypic plasticity in response to host and environment confounds species delimitation in Euphrasia. When grown in a common garden environment it is possible to identify some morphologically distinct taxa, though others represent morphologically similar shallow segregates. Trait differences present between some species and populations demonstrates the rapid evolution of distinct life history strategies in response to local ecological conditions."Manyhosts.csv" contains morphological measurements from one Euphrasia arctica population from North Berwick, Scotland, grown with eight hosts.
"Manyspecies.csv" contains morphological measurements of five Euphrasia species and six natural Euphrasia hybrids grown on a single host, Trifolium repens.
"Earlylate.csv" contains repeated growth measurements at different times of year, used in correlations of height at end of season.
"Wildcommon.csv" contains Euphrasia species grown in the common garden experiment and wild collected plants for trait comparisons.Data collection is detailed in the associated manuscript. Post collection data processing can be viewed at:
https://github.com/Euphrasiologist/phenotypic_plasticity_euphrasi
Experimental Controlled-NOT Logic Gate for Single Photons in the Coincidence Basis
We report a proof-of-principle demonstration of a probabilistic
controlled-NOT gate for single photons. Single-photon control and target qubits
were mixed with a single ancilla photon in a device constructed using only
linear optical elements. The successful operation of the controlled-NOT gate
relied on post-selected three-photon interference effects which required the
detection of the photons in the output modes.Comment: 4 pages, 4 figures; minor change
Optical generation of matter qubit graph states
We present a scheme for rapidly entangling matter qubits in order to create
graph states for one-way quantum computing. The qubits can be simple 3-level
systems in separate cavities. Coupling involves only local fields and a static
(unswitched) linear optics network. Fusion of graph state sections occurs with,
in principle, zero probability of damaging the nascent graph state. We avoid
the finite thresholds of other schemes by operating on two entangled pairs, so
that each generates exactly one photon. We do not require the relatively slow
single qubit local flips to be applied during the growth phase: growth of the
graph state can then become a purely optical process. The scheme naturally
generates graph states with vertices of high degree and so is easily able to
construct minimal graph states, with consequent resource savings. The most
efficient approach will be to create new graph state edges even as qubits
elsewhere are measured, in a `just in time' approach. An error analysis
indicates that the scheme is relatively robust against imperfections in the
apparatus.Comment: 10 pages in 2 column format, includes 4 figures. Problems with
figures resolve
The best Of CafeLit 2011
Each story in this little volume is the right length and quality for enjoying as you sip the assigned drink in your favourite Creative Café. You need never feel alone again in a café. So what’s the mood today? Espresso? Earl Grey tea? Hot chocolate with marshmallows? You’ll find most drinks in our drinks index.
If you’re reading the café’s copy and you have your Kindle or iPhone with you, why not download the Kindle version? Or browse the CaféLit web site for more examples of CaféLit stories? http://cafelitcreativecafe.blogspot.com/ and http://creativecafeproject.co.uk/CafLit.aspx
CaféLit supports the Creative Café project
Generalized Fano lineshapes reveal exceptional points in photonic molecules
The optical behavior of coupled systems, in which the breaking of parity and time-reversal symmetry occurs, is drawing increasing attention to address the physics of the exceptional point singularity, i.e., when the real and imaginary parts of the normal-mode eigenfrequencies coincide. At this stage, fascinating phenomena are predicted, including electromagnetic-induced transparency and phase transitions. To experimentally observe the exceptional points, the near-field coupling to waveguide proposed so far was proved to work only in peculiar cases. Here, we extend the interference detection scheme, which lies at the heart of the Fano lineshape, by introducing generalized Fano lineshapes as a signature of the exceptional point occurrence in resonant-scattering experiments. We investigate photonic molecules and necklace states in disordered media by means of a near-field hyperspectral mapping. Generalized Fano profiles in material science could extend the characterization of composite nanoresonators, semiconductor nanostructures, and plasmonic and metamaterial devices
- …