6,351 research outputs found
A near deterministic linear optical CNOT gate
We show how to construct a near deterministic CNOT using several single
photons sources, linear optics, photon number resolving quantum non-demolition
detectors and feed-forward. This gate does not require the use of massively
entangled states common to other implementations and is very efficient on
resources with only one ancilla photon required. The key element of this gate
are non-demolition detectors that use a weak cross-Kerr nonlinearity effect to
conditionally generate a phase shift on a coherent probe, if a photon is
present in the signal mode. These potential phase shifts can then be measured
using highly efficient homodyne detection.Comment: 4 pages, 3 figure
Wigner Functions for Arbitrary Quantum Systems
The possibility of constructing a complete, continuous Wigner function for
any quantum system has been a subject of investigation for over 50 years. A key
system that has served to illustrate the difficulties of this problem has been
an ensemble of spins. Here we present a general and consistent framework for
constructing Wigner functions exploiting the underlying symmetries in the
physical system at hand. The Wigner function can be used to fully describe any
quantum system of arbitrary dimension or ensemble size.Comment: 5 pages, 3 figure
Quantum Nonlocality for a Mixed Entangled Coherent State
Quantum nonlocality is tested for an entangled coherent state, interacting
with a dissipative environment. A pure entangled coherent state violates Bell's
inequality regardless of its coherent amplitude. The higher the initial
nonlocality, the more rapidly quantum nonlocality is lost. The entangled
coherent state can also be investigated in the framework of Hilbert
space. The quantum nonlocality persists longer in Hilbert space.
When it decoheres it is found that the entangled coherent state fails the
nonlocality test, which contrasts with the fact that the decohered entangled
state is always entangled.Comment: 20 pages, 7 figures. To be published in J. Mod. Op
Efficient optical quantum information processing
Quantum information offers the promise of being able to perform certain
communication and computation tasks that cannot be done with conventional
information technology (IT). Optical Quantum Information Processing (QIP) holds
particular appeal, since it offers the prospect of communicating and computing
with the same type of qubit. Linear optical techniques have been shown to be
scalable, but the corresponding quantum computing circuits need many auxiliary
resources. Here we present an alternative approach to optical QIP, based on the
use of weak cross-Kerr nonlinearities and homodyne measurements. We show how
this approach provides the fundamental building blocks for highly efficient
non-absorbing single photon number resolving detectors, two qubit parity
detectors, Bell state measurements and finally near deterministic control-not
(CNOT) gates. These are essential QIP devicesComment: Accepted to the Journal of optics B special issue on optical quantum
computation; References update
Non-Markovian dynamics of a qubit
In this paper we investigate the non-Markovian dynamics of a qubit by
comparing two generalized master equations with memory. In the case of a
thermal bath, we derive the solution of the post-Markovian master equation
recently proposed in Ref. [A. Shabani and D.A. Lidar, Phys. Rev. A {\bf 71},
020101(R) (2005)] and we study the dynamics for an exponentially decaying
memory kernel. We compare the solution of the post-Markovian master equation
with the solution of the typical memory kernel master equation. Our results
lead to a new physical interpretation of the reservoir correlation function and
bring to light the limits of usability of master equations with memory for the
system under consideration.Comment: Replaced with published version (minor changes
Overcoming decoherence in the collapse and revival of spin Schr\"odinger cats
In addition to being a very interesting quantum phenomenon, Schr\"odinger cat
swapping has the potential for application in the preparation of quantum states
that could be used in metrology and other quantum processing. We study in
detail the effects of field decoherence on a cat-swapping system comprising a
set of identical qubits, or spins, all coupled to a field mode. We demonstrate
that increasing the number of spins actually mitigates the effects of field
decoherence on the collapse and revival of a spin Schr\"odinger cat, which
could be of significant utility in quantum metrology and other quantum
processing.Comment: 4 pages, 2 figure
Quantum Repeaters using Coherent-State Communication
We investigate quantum repeater protocols based upon atomic
qubit-entanglement distribution through optical coherent-state communication.
Various measurement schemes for an optical mode entangled with two spatially
separated atomic qubits are considered in order to nonlocally prepare
conditional two-qubit entangled states. In particular, generalized measurements
for unambiguous state discrimination enable one to completely eliminate
spin-flip errors in the resulting qubit states, as they would occur in a
homodyne-based scheme due to the finite overlap of the optical states in phase
space. As a result, by using weaker coherent states, high initial fidelities
can still be achieved for larger repeater spacing, at the expense of lower
entanglement generation rates. In this regime, the coherent-state-based
protocols start resembling single-photon-based repeater schemes.Comment: 11 pages, 8 figure
Minimally invasive reduction and percutaneous fixation versus open reduction and internal fixation for displaced intra-articular calcaneal fractures : a systematic review of the literature
The aim of this article is to systematically identify and analyse research evidence available to compare the outcomes of minimally invasive reduction and percutaneous fixation (MIRPF) versus open reduction and internal fixation (ORIF) for displaced intra-articular calcaneal fractures.
Articles from 2000 to 2016 were searched through MEDLINE (PubMed), Cochrane Library, Embase, ScienceDirect, Scopus and ISI Web of Knowledge using Boolean logic and text words. Of the 570 articles identified initially, nine were selected including three randomized controlled trials and six retrospective comparative studies.
All nine studies had a total of 1,031 patients with 1,102 displaced intra-articular calcaneal fractures. Mean follow-up was 33 months. Of these, 602 (54.6%) were treated with MIRPF and 500 (45.4%) were treated with ORIF.
Overall incidence of wound-related complications in patients treated with MIRPF was 4.3% (0% to 13%) compared with 21.2% (11.7% to 35%) in the ORIF group
Functional outcomes were reported to be better in the minimally invasive group in all studies; however, the results did not reach statistical significance in some studies. All the studies had methodological flaws that put them at either ‘unclear’ or ‘high’ risk of bias for multiple domains.
Overall quality of the available evidence is poor in support of either surgical technique due to small sample size, flaws in study designs and high risk of bias for various elements. Individual studies have reported minimally invasive techniques to be an effective alternative with lower risk of wound complications and better functional outcomes.</ul
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