4,050 research outputs found
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
Demonstration of a simple entangling optical gate and its use in Bell-state analysis
We demonstrate a new architecture for an optical entangling gate that is
significantly simpler than previous realisations, using partially-polarising
beamsplitters so that only a single optical mode-matching condition is
required. We demonstrate operation of a controlled-Z gate in both
continuous-wave and pulsed regimes of operation, fully characterising it in
each case using quantum process tomography. We also demonstrate a
fully-resolving, nondeterministic optical Bell-state analyser based on this
controlled-Z gate. This new architecture is ideally suited to guided optics
implementations of optical gates.Comment: 4 pages, 3 figures. v2: additional author, improved data and figures
(low res), some other minor changes. Accepted for publication in PR
Quantum process tomography of a controlled-NOT gate
We demonstrate complete characterization of a two-qubit entangling process -
a linear optics controlled-NOT gate operating with coincident detection - by
quantum process tomography. We use maximum-likelihood estimation to convert the
experimental data into a physical process matrix. The process matrix allows
accurate prediction of the operation of the gate for arbitrary input states,
and calculation of gate performance measures such as the average gate fidelity,
average purity and entangling capability of our gate, which are 0.90, 0.83 and
0.73, respectively.Comment: 4 pages, 2 figures. v2 contains new data corresponding to improved
gate operation. Figure quality slightly reduced for arXi
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Investigation of Photoplethysmographic Changes using a Static Compression Model of Spinal Cord Injury
Little is known about cell death in spinal cord tissue following compression injury, despite compression being a key component of spinal injuries. Currently models are used to mimic compression injury in animals and the effects of the compression evaluated by observing the extent and duration of recovery of normal motor function in the days and weeks following the injury. A fiber-optic photoplethysmography system was used to investigate whether pulsation of the small arteries in the spinal cord occurred before, during and after compressive loads were applied to the tissue. It was found that the signal amplitudes were reduced and this reduction persisted for at least five minutes after the compression ceased. It is hoped that results from this preliminary study may improve knowledge of the mechanism of spinal cord injury
Experimental demonstration of Shor's algorithm with quantum entanglement
Shor's powerful quantum algorithm for factoring represents a major challenge
in quantum computation and its full realization will have a large impact on
modern cryptography. Here we implement a compiled version of Shor's algorithm
in a photonic system using single photons and employing the non-linearity
induced by measurement. For the first time we demonstrate the core processes,
coherent control, and resultant entangled states that are required in a
full-scale implementation of Shor's algorithm. Demonstration of these processes
is a necessary step on the path towards a full implementation of Shor's
algorithm and scalable quantum computing. Our results highlight that the
performance of a quantum algorithm is not the same as performance of the
underlying quantum circuit, and stress the importance of developing techniques
for characterising quantum algorithms.Comment: 4 pages, 5 figures + half-page additional online materia
Rayleigh and depinning instabilities of forced liquid ridges on heterogeneous substrates
Depinning of two-dimensional liquid ridges and three-dimensional drops on an
inclined substrate is studied within the lubrication approximation. The
structures are pinned to wetting heterogeneities arising from variations of the
strength of the short-range polar contribution to the disjoining pressure. The
case of a periodic array of hydrophobic stripes transverse to the slope is
studied in detail using a combination of direct numerical simulation and
branch-following techniques. Under appropriate conditions the ridges may either
depin and slide downslope as the slope is increased, or first breakup into
drops via a transverse instability, prior to depinning. The different
transition scenarios are examined together with the stability properties of the
different possible states of the system.Comment: Physics synopsis link:
http://physics.aps.org/synopsis-for/10.1103/PhysRevE.83.01630
Measuring Entangled Qutrits and Their Use for Quantum Bit Commitment
We produce and holographically measure entangled qudits encoded in transverse
spatial modes of single photons. With the novel use of a quantum state
tomography method that only requires two-state superpositions, we achieve the
most complete characterisation of entangled qutrits to date. Ideally, entangled
qutrits provide better security than qubits in quantum bit-commitment: we model
the sensitivity of this to mixture and show experimentally and theoretically
that qutrits with even a small amount of decoherence cannot offer increased
security over qubits.Comment: Paper updated to match published version; 5 pages, 4 figures, images
have been included at slightly lower quality for the archiv
Study protocol for a double blind, randomised, placebo-controlled trial of continuous subpectoral local anaesthetic infusion for pain and shoulder function following mastectomy: SUB-pectoral Local anaesthetic Infusion following MastEctomy (SUBLIME) study.
INTRODUCTION: Over 16 000 mastectomies are performed in England and Wales annually. Acute postoperative pain and nausea are common. The most frequently occurring long-term complications are chronic pain (up to 50%) and reduced shoulder function (reported at 35%). Regional techniques that improve acute postoperative pain relief may reduce the incidence of these complications. This study assesses the effectiveness of a 24-hour continuous local anaesthetic in the subpectoral plane in improving postoperative pain and quality of life in patients undergoing mastectomy. METHODS AND ANALYSIS: This is a randomised, double blind, placebo-controlled, two-centre, parallel group trial in women undergoing mastectomy with or without axillary involvement. One hundred and sixty participants will be randomised in a 1:1 ratio to receive either 0.25% levobupivacaine or 0.9% saline by subpectoral infusion postoperatively for 24 h. All participants will be provided with an intravenous morphine patient-controlled analgesia (PCA) system. Participants will be followed-up for 24 h in hospital and at approximately 14 days and 6 months postoperatively. Joint primary outcome measures are total morphine consumption and total pain score (captured via patient-recorded visual analogue scale (VAS) 4 hourly) during the first 24 h postoperatively. Primary statistical analysis of total pain is based on the area under the curve of pain versus time graph. Secondary outcomes include PCA attempts in first 24 h; VAS pain scores and shoulder function by goniometry at 24 h, 14 days (approximately) and 6 months; Verbal Rating Scale pain scores in first 24 h; Brief Pain Inventory and Oxford Shoulder Score at 6 months; duration of hospital stay; incidence of postoperative nausea and vomiting; cost-effectiveness. ETHICS AND DISSEMINATION: The study is approved by the South West England Research Ethics Committee (12/SW/0149). RESULTS: will be published in a peer-reviewed journal and presented at local, national and international scientific meetings. TRIAL REGISTRATION: ISRCTN46621916. EudraCT 2011-005775-16
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