Optical Quantum Computation

We review the field of Optical Quantum Computation, considering the various implementations that have been proposed and the experimental progress that has been made toward realizing them. We examine both linear and nonlinear approaches and both particle and field encodings. In particular we discuss the prospects for large scale optical quantum computing in terms of the most promising physical architectures and the technical requirements for realizing them

Phase-dependent decoherence of optical transitions in Pr3+:LaF3 in the presence of a driving field

The decoherence times of orthogonally phased components of the optical transition dipole moment in a two-level system have been observed to differ by an order of magnitude. This phase anisotropy is observed in coherent transient experiments where an optical driving field is present during extended periods of decoherence. The decoherence time of the component of the dipole moment in phase with the driving field is extended compared to T_2, obtained from two-pulse photon echoes, in analogy with the spin locking technique of NMR.Comment: 5 pages, 2 figures; replaced with published versio

Violation of the Leggett-Garg inequality with weak measurements of photons

By weakly measuring the polarization of a photon between two strong polarization measurements, we experimentally investigate the correlation between the appearance of anomalous values in quantum weak measurements, and the violation of realism and non-intrusiveness of measurements. A quantitative formulation of the latter concept is expressed in terms of a Leggett-Garg inequality for the outcomes of subsequent measurements of an individual quantum system. We experimentally violate the Leggett-Garg inequality for several measurement strengths. Furthermore, we experimentally demonstrate that there is a one-to-one correlation between achieving strange weak values and violating the Leggett-Garg inequality.Comment: 5 pages, 4 figure

Creation of Maximally Entangled Photon Number States using Optical Fibre Multiports

We theoretically demonstrate a method for producing the maximally path-entangled state (1/Sqrt[2]) (|N,0> + exp[iN phi] |0,N>) using intensity-symmetric multiport beamsplitters, single photon inputs, and either photon-counting postselection or conditional measurement. The use of postselection enables successful implementation with non-unit efficiency detectors. We also demonstrate how to make the same state more conveniently by replacing one of the single photon inputs by a coherent state

Entanglement-enhanced measurement of a completely unknown phase

The high-precision interferometric measurement of an unknown phase is the basis for metrology in many areas of science and technology. Quantum entanglement provides an increase in sensitivity, but present techniques have only surpassed the limits of classical interferometry for the measurement of small variations about a known phase. Here we introduce a technique that combines entangled states with an adaptive algorithm to precisely estimate a completely unspecified phase, obtaining more information per photon that is possible classically. We use the technique to make the first ab initio entanglement-enhanced optical phase measurement. This approach will enable rapid, precise determination of unknown phase shifts using interferometry.Comment: 6 pages, 4 figure

Septic Shock and Sepsis Syndrome in Obstetric Patients

Septic shock is a life-threatening clinical syndrome that, despite its rare occurrence in obstetrics, remains a leading cause of maternal mortality. Its pathophysiology is explained by a profound systemic response to a complex variety of host cellular and humoral mediators elaborated after exposure to microbial toxins. Early recognition, prompt diagnostic workup, and immediate initiation of therapy improve outcomes. Therefore, recent publications have popularized the concept of the “sepsis syndrome,” a preshock list of clinical criteria associated with progressive sepsis. Needed diagnostic studies should never be withheld because of “pregnancy concerns.” With critically ill patients, the risk-to-benefit ratio supports the use of these diagnostic studies in almost all circumstances. Standard therapy is directed principally at restoring tissue perfusion by intravascular volume expansion and in some instances vasoactive pharmacological intervention. Simultaneously, identification of the source of infection and commencement of appropriate empiric antibiotic treatment are critical. In some cases, surgical abscess drainage or debridement of infected necrotic tissue will need to be considered. Novel approaches to treatment that attempt to reduce the systemic response to microbial toxins are promising and under active investigation. Pregnancy-specific considerations include the following: 1) initial signs or symptoms of septic shock may be masked by normal physiologic alterations of pregnancy; 2) a mixed polymicrobial group of organisms, consistent with lower genital tract flora, should be anticipated; and 3) initial therapy should be directed at maternal concerns since adverse fetal effects are most likely the result of maternal decompensation

The state of agricultural credit in New Zealand

In this paper the subject of agricultural credit has been subdivided into three sections covering background, borrowing, and lending. The background covers some of the changes in the New Zealand economy and government policies which have affected both borrowers and lenders in the agricultural sector, and consequently the amount and form of credit used. The section on borrowing (Section 3) examines the present credit needs of farmers, in particular the apparent trends towards increased equity and greater difficulty in servicing debt. The lending section (Section 4) examines the roles of government and private lending institutions in the field of agricultural credit and changes in the amount and form of credit available

Solid state coherent transient measurements using hard optical pulses

An isolated and spectrally narrow absorptive feature is prepared via a novel spectral hole burning process in an inhomogeneously broadened optical transition in Eu3+:Y2SiO5. With the narrow feature it is shown that it is feasible to apply complex optical pulse sequences analogous to rf pulse sequences used extensively in NMR