322 research outputs found
Counting Statistics of Many-Particle Quantum Walks
We study quantum walks of many non-interacting particles on a beam splitter
array, as a paradigmatic testing ground for the competition of single- and
many-particle interference in a multi-mode system. We derive a general
expression for multi-mode particle-number correlation functions, valid for
bosons and fermions, and infer pronounced signatures of many-particle
interferences in the counting statistics.Comment: 4 pages, 4 figure
Towards symmetric scheme for superdense coding between multiparties
Recently Liu, Long, Tong and Li [Phys. Rev. A 65, 022304 (2002)] have
proposed a scheme for superdense coding between multiparties. This scheme seems
to be highly asymmetric in the sense that only one sender effectively exploits
entanglement. We show that this scheme can be modified in order to allow more
senders to benefit of the entanglement enhanced information transmission.Comment: 6 page
Creation of macroscopic superposition states from arrays of Bose-Einstein condensates
We consider how macroscopic quantum superpositions may be created from arrays
of Bose-Einstein condensates. We study a system of three condensates in Fock
states, all with the same number of atoms and show that this has the form of a
highly entangled superposition of different quasi-momenta. We then show how, by
partially releasing these condensates and detecting an interference pattern
where they overlap, it is possible to create a macroscopic superposition of
different relative phases for the remaining portions of the condensates. We
discuss methods for confirming these superpositions.Comment: 7 pages, 5 figure
Thrombolyse der Arteria cerebri media
Zusammenfassung: In den ersten 3h nach Eintritt eines akuten ischämischen Hirninfarkts ist die intravenöse Thrombolyse (IVT) die evidenzbasierte Therapie (IVT 3-4,5h: "off-label use" mit Einverständnis des Patienten). Die intraarterielle Thrombolyse (IAT) führt in der A.cerebri media (ACM) allerdings häufiger zur Rekanalisation als die IVT. Daher ist die IAT in dafür ausgerüsteten Kliniken ergänzend oder alternativ zur IVT bis zu 6h nach Symptombeginn zu erwäge
Coherent Time Evolution and Boundary Conditions of Two-Photon Quantum Walks
Multi-photon quantum walks in integrated optics are an attractive controlled
quantum system, that can mimic less readily accessible quantum systems and
exhibit behavior that cannot in general be accurately replicated by classical
light without an exponential overhead in resources. The ability to observe time
evolution of such systems is important for characterising multi-particle
quantum dynamics---notably this includes the effects of boundary conditions for
walks in spaces of finite size. Here we demonstrate the coherent evolution of
quantum walks of two indistinguishable photons using planar arrays of 21
evanescently coupled waveguides fabricated in silicon oxynitride technology. We
compare three time evolutions, that follow closely a model assuming unitary
evolution, corresponding to three different lengths of the array---in each case
we observe quantum interference features that violate classical predictions.
The longest array includes reflecting boundary conditions.Comment: 7 pages,7 figure
Locally induced hypothermia for treatment of acute ischaemic stroke: a physical feasibility study
During the treatment of stroke by local intra-arterial thrombolysis (LIT) it is frequently possible to pass the blood clot with a micro-catheter, allowing perfusion of brain tissue distally to the occlusion. This possibility allows for new early treatments of ischaemic brain tissue, even before the blood clot has been removed. One potential new approach to preserve brain tissue at risk may be locally induced endovascular hypothermia. Physical parameters such as the required micro-catheter input pressure, output velocity and flow rates, and a heat exchange model, applicable in the case of a micro-catheter placed within a guiding catheter, are presented. Also, a simple cerebral temperature model is derived that models the temperature response of the brain to the perfusion with coolant fluids. Based on this model, an expression has been derived for the time needed to reach a certain cerebral target temperature. Experimental in vitro measurements are presented that confirm the usability of standard commercially available micro-catheters to induce local hypothermia of the brain. If applied in vivo, the model predicts a local cooling rate of ischaemic brain tissue of 300g of approximately 1°C in 1min, which is up to a factor 30-times faster than the time-consuming systemic hypothermia via the skin. Systemic body temperature is only minimally affected by application of local hypothermia, thus avoiding many limitations and complications known in systemic hypothermi
Experimental Realization of Teleporting an Unknown Pure Quantum State via Dual Classical and Einstein-Podolski-Rosen Channels
We report on a quantum optical experimental implementation of teleportation
of unknown pure quantum states. This realizes all the nonlocal aspects of the
original scheme proposed by Bennett et al. and is equivalent to it up to a
local operation. We exhibit results for the teleportation of a linearly
polarized state and of an elliptically polarized state. We show that the
experimental results cannot be explained in terms of a classical channel alone.Comment: 11 pages LaTeX, 3 figures, 1 page figures captions. The figures and
figures captions are not encapsulated; please print them separatel
Unconditional Continuous Variable Dense Coding
We investigate the conditions under which unconditional dense coding can be
achieved using continuous variable entanglement. We consider the effect of
entanglement impurity and detector efficiency and discuss experimental
verification. We conclude that the requirements for a strong demonstration are
not as stringent as previously thought and are within the reach of present
technology
Extreme nonlocality with one photon
Quantum nonlocality is typically assigned to systems of two or more well
separated particles, but nonlocality can also exist in systems consisting of
just a single particle, when one considers the subsystems to be distant spatial
field modes. Single particle nonlocality has been confirmed experimentally via
a bipartite Bell inequality. In this paper, we introduce an N-party Hardy-like
proof of impossibility of local elements of reality and a Bell inequality for
local realistic theories for a single particle superposed symmetrical over N
spatial field modes (i.e. a N qubit W state). We show that, in the limit of
large N, the Hardy-like proof effectively becomes an all-versus nothing (or
GHZ-like) proof, and the quantum-classical gap of the Bell inequality tends to
be same of the one in a three-particle GHZ experiment. We detail how to test
the nonlocality in realistic systems.Comment: 11 single column pages, 2 figures; v3 now includes a Bell inequality
in addition to the results in the previous versio
Hiding bits in Bell states
We present a scheme for hiding bits in Bell states that is secure even when
the sharers Alice and Bob are allowed to carry out local quantum operations and
classical communication. We prove that the information that Alice and Bob can
gain about a hidden bit is exponentially small in , the number of qubits in
each share, and can be made arbitrarily small for hiding multiple bits. We
indicate an alternative efficient low-entanglement method for preparing the
shared quantum states. We discuss how our scheme can be implemented using
present-day quantum optics.Comment: 4 pages RevTex, 1 figure, various small changes and additional
paragraph on optics implementatio
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