663 research outputs found
Revisiting the quantum Szilard engine with fully quantum considerations
By considering level shifting during the insertion process we revisit the
quantum Szilard engine (QSZE) with fully quantum consideration. We derive the
general expressions of the heat absorbed from thermal bath and the total work
done to the environment by the system in a cycle with two different cyclic
strategies. We find that only the quantum information contributes to the
absorbed heat, and the classical information acts like a feedback controller
and has no direct effect on the absorbed heat. This is the first demonstration
of the different effects of quantum information and classical information for
extracting heat from the bath in the QSZE. Moreover, when the well width
or the temperature of the bath
the QSZE reduces to the classical Szilard engine (CSZE), and the total work
satisfies the relation as obtained by
Sang Wook Kim et al. [Phys. Rev. Lett. 106, 070401 (2011)] for one particle
case.Comment: 17 pages, 3 figures, to be published in Annals of Physics(NY
A new small-bodied azhdarchoid pterosaur from the Lower Cretaceous of England and its implications for pterosaur anatomy, diversity and phylogeny
BACKGROUND: Pterosaurs have been known from the Cretaceous sediments of the Isle of Wight (southern England, United Kingdom) since 1870. We describe the three-dimensional pelvic girdle and associated vertebrae of a small near-adult pterodactyloid from the Atherfield Clay Formation (lower Aptian, Lower Cretaceous). Despite acknowledged variation in the pterosaur pelvis, previous studies have not adequately sampled or incorporated pelvic characters into phylogenetic analyses. METHODOLOGY/PRINCIPAL FINDINGS: The new specimen represents the new taxon Vectidraco daisymorrisae gen. et sp. nov., diagnosed by the presence of a concavity posterodorsal to the acetabulum and the form of its postacetabular process on the ilium. Several characters suggest that Vectidraco belongs to Azhdarchoidea. We constructed a pelvis-only phylogenetic analysis to test whether the pterosaur pelvis carries a useful phylogenetic signal. Resolution in recovered trees was poor, but they approximately matched trees recovered from analyses of total evidence. We also added Vectidraco and our pelvic characters to an existing total-evidence matrix for pterosaurs. Both analyses recovered Vectidraco within Azhdarchoidea. CONCLUSIONS/ SIGNIFICANCE: The Lower Cretaceous strata of western Europe have yielded members of several pterosaur lineages, but Aptian pterosaurs from western Europe are rare. With a pelvis length of 40 mm, the new animal would have had a total length of c. 350 mm, and a wingspan of c. 750 mm. Barremian and Aptian pterodactyloids from western Europe show that small-bodied azhdarchoids lived alongside ornithocheirids and istiodactylids. This assemblage is similar in terms of which lineages are represented to the coeval beds of Liaoning, China; however, the number of species and specimens present at Liaoning is much higher. While the general phylogenetic composition of western European and Chinese communities appear to have been approximately similar, the differences may be due to different palaeoenvironmental and depositional settings. The western Europe pterodactyloid record may therefore be artificially low in diversity due to preservational factors
Experimental Demonstration of Five-photon Entanglement and Open-destination Teleportation
Universal quantum error-correction requires the ability of manipulating
entanglement of five or more particles. Although entanglement of three or four
particles has been experimentally demonstrated and used to obtain the extreme
contradiction between quantum mechanics and local realism, the realization of
five-particle entanglement remains an experimental challenge. Meanwhile, a
crucial experimental challenge in multi-party quantum communication and
computation is the so-called open-destination teleportation. During
open-destination teleportation, an unknown quantum state of a single particle
is first teleported onto a N-particle coherent superposition to perform
distributed quantum information processing. At a later stage this teleported
state can be readout at any of the N particles for further applications by
performing a projection measurement on the remaining N-1 particles. Here, we
report a proof-of-principle demonstration of five-photon entanglement and
open-destination teleportation. In the experiment, we use two entangled photon
pairs to generate a four-photon entangled state, which is then combined with a
single photon state to achieve the experimental goals. The methods developed in
our experiment would have various applications e.g. in quantum secret sharing
and measurement-based quantum computation.Comment: 19 pages, 4 figures, submitted for publication on 15 October, 200
Sisyphus cooling and amplification by a superconducting qubit
Laser cooling of the atomic motion paved the way for remarkable achievements
in the fields of quantum optics and atomic physics, including Bose-Einstein
condensation and the trapping of atoms in optical lattices. More recently
superconducting qubits were shown to act as artificial two-level atoms,
displaying Rabi oscillations, Ramsey fringes, and further quantum effects.
Coupling such qubits to resonators brought the superconducting circuits into
the realm of quantum electrodynamics (circuit QED). It opened the perspective
to use superconducting qubits as micro-coolers or to create a population
inversion in the qubit to induce lasing behavior of the resonator. Furthering
these analogies between quantum optical and superconducting systems we
demonstrate here Sisyphus cooling of a low frequency LC oscillator coupled to a
near-resonantly driven superconducting qubit. In the quantum optics setup the
mechanical degrees of freedom of an atom are cooled by laser driving the atom's
electronic degrees of freedom. Here the roles of the two degrees of freedom are
played by the LC circuit and the qubit's levels, respectively. We also
demonstrate the counterpart of the Sisyphus cooling, namely Sisyphus
amplification. Parallel to the experimental demonstration we analyze the system
theoretically and find quantitative agreement, which supports the
interpretation and allows us to estimate system parameters.Comment: 7 pages, 4 figure
Experimental Quantum Teleportation of a Two-Qubit Composite System
Quantum teleportation, a way to transfer the state of a quantum system from
one location to another, is central to quantum communication and plays an
important role in a number of quantum computation protocols. Previous
experimental demonstrations have been implemented with photonic or ionic
qubits. Very recently long-distance teleportation and open-destination
teleportation have also been realized. Until now, previous experiments have
only been able to teleport single qubits. However, since teleportation of
single qubits is insufficient for a large-scale realization of quantum
communication and computation2-5, teleportation of a composite system
containing two or more qubits has been seen as a long-standing goal in quantum
information science. Here, we present the experimental realization of quantum
teleportation of a two-qubit composite system. In the experiment, we develop
and exploit a six-photon interferometer to teleport an arbitrary polarization
state of two photons. The observed teleportation fidelities for different
initial states are all well beyond the state estimation limit of 0.40 for a
two-qubit system. Not only does our six-photon interferometer provide an
important step towards teleportation of a complex system, it will also enable
future experimental investigations on a number of fundamental quantum
communication and computation protocols such as multi-stage realization of
quantum-relay, fault-tolerant quantum computation, universal quantum
error-correction and one-way quantum computation.Comment: 16pages, 4 figure
Reducing recurrent stroke: Methodology of the motivational interviewing in stroke (MIST) randomized clinical trial
Rationale
Recurrent stroke is prevalent in both developed and developing countries, contributing significantly to disability and death. Recurrent stroke rates can be reduced by adequate risk factor management. However, adherence to prescribed medications and lifestyle changes recommended by physicians at discharge after stroke is poor, leading to a large number of preventable recurrent strokes. Using behavior change methods such as Motivational Interviewing early after stroke occurrence has the potential to prevent recurrent stroke.
Aims and/or hypothesis
The overall aim of the study is to determine the effectiveness of motivational interviewing in improving adherence to medication and lifestyle changes recommended by treating physicians at and after hospital discharge in stroke patients 12 months poststroke to reduce risk factors for recurrent stroke.
Design
Recruitment of 430 first-ever stroke participants will occur in the Auckland and Waikato regions. Randomization will be to intervention or usual care groups. Participants randomized to intervention will receive four motivational interviews and five follow-up assessments over 12 months. Nonintervention participants will be assessed at the same time points.
Study outcomes
Primary outcome measures are changes in systolic blood pressure and low-density lipoprotein levels 12 months poststroke. Secondary outcomes include self-reported adherence and barriers to prescribed medications, new cardiovascular events (including stroke), changes in quality of life, and mood.
Discussion
The results of the motivational interviewing in stroke trial will add to our understanding of whether motivational interviewing may be potentially beneficial in the management of stroke and other diseases where similar lifestyle factors or medication adherence are relevant
Memory-built-in quantum teleportation with photonic and atomic qubits
The combination of quantum teleportation and quantum memory of photonic
qubits is essential for future implementations of large-scale quantum
communication and measurement-based quantum computation. Both steps have been
achieved separately in many proof-of-principle experiments, but the
demonstration of memory-built-in teleportation of photonic qubits remains an
experimental challenge. Here, we demonstrate teleportation between photonic
(flying) and atomic (stationary) qubits. In our experiment, an unknown
polarization state of a single photon is teleported over 7 m onto a remote
atomic qubit that also serves as a quantum memory. The teleported state can be
stored and successfully read out for up to 8 micro-second. Besides being of
fundamental interest, teleportation between photonic and atomic qubits with the
direct inclusion of a readable quantum memory represents a step towards an
efficient and scalable quantum network.Comment: 19 pages 3 figures 1 tabl
Reducing recurrent stroke: methodology of the motivational interviewing in stroke (MIST) randomized clinical trial
Recurrent stroke is prevalent in both developed and developing countries, contributing significantly to disability and death. Recurrent stroke rates can be reduced by adequate risk factor management. However, adherence to prescribed medications and lifestyle changes recommended by physicians at discharge after stroke is poor, leading to a large number of preventable recurrent strokes. Using behavior change methods such as Motivational Interviewing early after stroke occurrence has the potential to prevent recurrent stroke
Detection of multipartite entanglement with two-body correlations
We show how to detect entanglement with criteria built from simple two-body
correlation terms. Since many natural Hamiltonians are sums of such correlation
terms, our ideas can be used to detect entanglement by energy measurement. Our
criteria can straightforwardly be applied for detecting different forms of
multipartite entanglement in familiar spin models in thermal equilibrium.Comment: 5 pages including 2 figures, LaTeX; for the proceedings of the DPG
spring meeting, Berlin, March 200
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