4,564 research outputs found
Experimentally generating and tuning robust entanglement between photonic qubits
We generate and study the entanglement properties of novel states composed of
three polarisation-encoded photonic qubits. By varying a single experimental
parameter we can coherently move from a fully separable state to a maximally
robust W state, while at all times preserving an optimally robust, symmetric
entanglement configuration. We achieve a high fidelity with these
configurations experimentally, including the highest reported W state fidelity.Comment: lower print quality for arxiv figure
Behaviour of dairy cows on organic and non-organic farms
There is an increasing number of organic dairy farms in the UK. The aim of this study is to compare behaviour of dairy cows on organic and non-organic farms. Twenty organic and 20 non-organic farms throughout the UK were visited over two winters (2004/05 and 2005/06). Organic and non-organic farms were paired for housing type, herd size, milk production traits and location. The number of cows feeding was counted every fifteen minutes for 4.5 h after new feed was available post morning milking. Behaviour at the feed-face was recorded for 60 minutes and aggressive interactions between cows were quantified. Farm type had no effect on numbers of cows feeding. There were more interactions between cows feeding at open feed-faces compared to head-bale barriers. At open feed-faces, there were more interactions on organic farms than non-organic. It is possible that organic cows were hungrier than non-organic cows after the arrival of new feed
Generation of Hyperentangled Photons Pairs
We experimentally demonstrate the first quantum system entangled in every
degree of freedom (hyperentangled). Using pairs of photons produced in
spontaneous parametric downconversion, we verify entanglement by observing a
Bell-type inequality violation in each degree of freedom: polarization, spatial
mode and time-energy. We also produce and characterize maximally hyperentangled
states and novel states simultaneously exhibiting both quantum and classical
correlations. Finally, we report the tomography of a 2x2x3x3 system
(36-dimensional Hilbert space), which we believe is the first reported photonic
entangled system of this size to be so characterized.Comment: 5 pages, 3 figures, 1 table, published versio
Choice of Measurement Sets in Qubit Tomography
Optimal generalized measurements for state estimation are well understood.
However, practical quantum state tomography is typically performed using a
fixed set of projective measurements and the question of how to choose these
measurements has been largely unexplored in the literature. In this work we
develop theoretical asymptotic bounds for the average fidelity of pure qubit
tomography using measurement sets whose axes correspond to vertices of Platonic
solids. We also present complete simulations of maximum likelihood tomography
for mixed qubit states using the Platonic solid measurements. We show that
overcomplete measurement sets can be used to improve the accuracy of
tomographic reconstructions.Comment: 13 Pages, 6 figure
Theory of Capillary Tension and Interfacial Dynamics of Motility-Induced Phases
The statistical mechanics of equilibrium interfaces has been well-established
for over a half century. In the last decade, a wealth of observations have made
increasingly clear that a new perspective is required to describe interfaces
arbitrarily far from equilibrium. In this Letter, beginning from microscopic
particle dynamics that break time-reversal symmetry, we systematically derive
the interfacial dynamics of coexisting motility-induced phases. Doing so allows
us to identify the athermal energy scale that excites interfacial fluctuations
and the nonequilibrium surface tension that resists these excitations. In
addition to establishing an active capillary-wave theory, our theory identifies
that, in contrast to equilibrium fluids, this active surface tension contains
contributions arising from nonconservative forces which act to suppress
interfacial fluctuations. The identified contribution bares a remarkable
resemblance with that envisioned by Edwards and Wilkinson in their description
of the surface of athermal granular materials, suggesting that
dynamically-stabilized interfaces may be a phenomenon common to a wide class of
nonequilibrium systems.Comment: Comments welcome
Manipulating biphotonic qutrits
Quantum information carriers with higher dimension than the canonical qubit
offer significant advantages. However, manipulating such systems is extremely
difficult. We show how measurement induced non-linearities can be employed to
dramatically extend the range of possible transforms on biphotonic qutrits; the
three level quantum systems formed by the polarisation of two photons in the
same spatio-temporal mode. We fully characterise the biphoton-photon
entanglement that underpins our technique, thereby realising the first instance
of qubit-qutrit entanglement. We discuss an extension of our technique to
generate qutrit-qutrit entanglement and to manipulate any bosonic encoding of
quantum information.Comment: 4 pages, 4 figure
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