PubMed Health⌕ Search

Biomedical subjects

H M Wiseman

Publications and source records attributed to H M Wiseman.

16 recordsLinked to original sources
PubMed2005

Measurement of quantum weak values of photon polarization.

We experimentally determine weak values for a single photon's polarization, obtained via a weak measurement that employs a two-photon entangling operation, and postselection. The weak values cannot be explained by a semiclassical wave theory, due to the two-photon entanglement. We observe the variation in the size of the weak value with measurement strength, obtaining an average measurement of the S1 Stokes parameter more than an order of magnitude outside of the operator's spectrum for the smallest measurement strengths.

Journal Article↗
PubMed2005

Optimal unravellings for feedback control in linear quantum systems.

For quantum systems with linear dynamics in phase space much of classical feedback control theory applies. However, there are some questions that are sensible only for the quantum case: Given a fixed interaction between the system and the environment what is the optimal measurement on the environment for a particular control problem? We show that for a broad class of optimal (state-based) control problems (the stationary linear-quadratic-Gaussian class), this question is a semidefinite program. Moreover, the answer also applies to Markovian (current-based) feedback.

Journal Article↗
PubMed2003

Entanglement of indistinguishable particles shared between two parties.

Using an operational definition we quantify the entanglement, E(P), between two parties who share an arbitrary pure state of N indistinguishable particles. We show that E(P)< or =E(M), where E(M) is the bipartite entanglement calculated from the mode-occupation representation. Unlike E(M), E(P) is superadditive. For example, E(P)=0 for any single-particle state, but the state |1>|1>, where both modes are split between the two parties, has E(P)=1/2. We discuss how this relates to quantum correlations between particles, for both fermions and bosons.

Journal Article↗
PubMed2003

Entanglement constrained by superselection rules.

Bipartite entanglement may be reduced if there are restrictions on allowed local operations. We introduce the concept of a generalized superselection rule to describe such restrictions, and quantify the entanglement constrained by it. We show that ensemble quantum information processing, where elements in the ensemble are not individually addressable, is subject to the superselection rule associated with the symmetric group (the group of permutations of elements). We prove that even for an ensemble comprising many pairs of qubits, each pair described by a pure Bell state, the entanglement per element constrained by this superselection rule goes to zero for a large number of elements.

Journal Article↗
PubMed2002

Capture and release of a conditional state of a cavity QED system by quantum feedback.

Detection of a single photon escaping an optical cavity QED system prepares a nonclassical state of the electromagnetic field. The evolution of the state can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured (stabilized) and then released. This is observed by a conditional intensity measurement that shows suppression of vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return.

Journal Article↗
PubMed2001

Inequivalence of pure state ensembles for open quantum systems: the preferred ensembles are those that are physically realizable.

An open quantum system in steady state rho(ss) can be represented by a weighted ensemble of pure states rho(ss) = [equation: see text] in infinitely many ways. A physically realizable (PR) ensemble is one for which some continuous measurement of the environment will collapse the system into a pure state /psi(t)>, stochastically evolving such that the proportion of time for which /psi(t)> = /psi(k)> equals Weierstrass p(k). Some, but not all, ensembles are PR. This constitutes the preferred ensemble fact. We present the necessary and sufficient conditions for a given ensemble to be PR, and illustrate the method by showing that the coherent state ensemble is not PR for an atom laser.

Journal Article↗
PubMed2001

Reducing the linewidth of an atom laser by feedback.

A continuous atom laser will almost certainly have a linewidth dominated by the effect of the atomic interaction energy, which turns fluctuations in the condensate atom number into fluctuations in the condensate frequency. These correlated fluctuations mean that information about the atom number could be used to reduce the frequency fluctuations, by controlling a spatially uniform potential. We show that feedback based on a physically reasonable quantum nondemolition measurement of the atom number of the condensate in situ can reduce the linewidth enormously.

Journal Article↗
PubMed1987

Accidental poisoning in childhood: a multicentre survey. 1. General epidemiology.

As background to a study of the effectiveness of packaging in preventing childhood poisoning, the National Poisons Information Service coordinated a prospective survey, in which 9 Accident and Emergency (A & E) departments and 5 paediatric departments, between July 1982 and February 1984, recorded 2043 cases of suspected accidental poisoning in children aged 0-60 months. The products implicated were drugs (59%), household products (37%) and plants (3%). The drugs most frequently implicated were analgesics, anxiolytics, cough medicines, oral contraceptives and drugs to supplement diet or treat dietary disorders. The most frequently implicated household products were cleaners such as bleach, detergent and disinfectant, and petroleum distillate. Seventy-five per cent of the children were 2 and 3-year-olds. Fifty-six per cent were male. Only 22% of the children had signs or symptoms on admission. In only 2 cases were these serious. Treatment other than ipecacuanha and/or oral fluids was seldom required. Of the cases where outcome was recorded, 56% were discharged from A & E. The rest were admitted to a ward; only 7 children were admitted to intensive care units. No child died. Comparison with HASS and other epidemiological surveys shows that these results are representative of national trends.

Accidents, Home↗
PubMed1987

Accidental poisoning in childhood: a multicentre survey. 2. The role of packaging in accidents involving medications.

To assess the effectiveness of child-resistant closures (CRCs) and unit dose packaging in preventing childhood poisoning with medications, a survey by 14 hospitals of accidental suspected poisoning in children under 5-years-old, was compared with a survey of a representative sample of households with children under 5 living in the catchment areas of the hospitals. Nine hundred and thirty-eight medications thought to have been ingested by 877 children were compared with 5827 medications found in households with children. The relationship between availability of packs or medications in the home and their involvement in accidents was quantified by means of an Accident Association Index (AAI). A low AAI indicated that the involvement of a pack or medication was less than expected from availability and therefore safe. A high AAI indicated that involvement was greater than expected and therefore unsafe. Medications involved in suspected poisoning were most frequently packed in containers without CRCs (63%) or transparent blisters (20%); both had high AAIs. CRCs, strips, sachets and opaque blisters had low AAIs. Analgesics, expectorants and gastrointestinal medications, had low AAIs, while oral contraceptives, hypnotics, sedative/tranquillizers, antidepressants, anticonvulsants, anti-emetics, and anti-infectives had high AAIs. Prescription medications were more frequently involved in accidents than over-the-counter (OTC) medications and had a higher AAI. Comparison of the AAIs of different kinds of medication in each of their various pack types showed that safe packaging reduced the risk from medications which had a high average AAI. Only 40% of medications were in their normal storage place at the time of the accident. Medicine and bathroom cabinets, and kitchen cupboards and drawers were the safest places to store medications. Handbags, fridges, and shelves or ledges in the bathroom were the most unsafe places. No pack had a low AAI when stored on open shelves indicating that safe packaging cannot compensate for unsafe storage. Other factors which influenced the involvement of medications in accidents were the intended user and the duration of storage. The results of the study have important implications for design of packaging for medications and for education of the public.

Accidents, Home↗
PubMed1983

Acute chlormethiazole poisoning in patients notified to the Poisons Unit, Guy's Hospital, 1978--1981.

1 Out of 493 patients with suspected acute chlormethiazole poisoning notified to the Poisons Unit, Guy's Hospital during 1978--1981, the diagnosis was confirmed either analytically or by detailed clinical information in 108 patients, 40 of whom had ingested chlormethiazole alone. 2 The principal signs reported indicate that the clinical features of acute chlormethiazole poisoning resemble those of barbiturate poisoning, with deep coma (n = 66), respiratory depression (n = 26) and hypotension (n = 17) in the severe cases. Five patients died as a result of early, profound respiratory depression. 3 In 53 survivors in whom toxicological analyses were performed, poisoning with chlormethiazole alone had a better prognosis than when ethanol or other drugs were also present, except in patients with hepatic or pulmonary disease or in the elderly. 4 These results emphasise that although patients poisoned with chlormethiazole who survive to reach hospital generally have a good prognosis, fatal respiratory complications often occur before the patient can be treated.

Adolescent↗
PubMed1980

Acute poisoning due to Wright's vaporizing fluid.

A 3-year survey is reported of acute poisoning by Wright's Vaporizing Fluid which covered a change in formulation from 90% cresol to 10% chlorocresol. Of 160 children (average age 2.5 years) and 12 adults, 21.5% had moderate symptoms, 7.5% had severe symptoms and one child died. Where incidents involved the old formulation very few patients escaped without symptoms and over 50% of thm had skin burns or moderate systemic symptoms. With the new formulation over 50% of the patients were asymptomatic and skin burns were uncommon. However there was no significant difference in the incidence of severe systemic symptoms between the formulations. The new formulation appears safer when small amounts of the fluid are ingested, but when larger amounts are involved it is potentially lethal. The case history of the fatal poisoning is presented.

Acute Disease↗
PubMed1980

Formic acid poisoning.

Forty-five cases of formic acid poisoning are reviewed. The metabolic and pathological consequences of such overdoses are considered. The consequences are discussed in relation to the amount of the acid ingested. The problems likely to be encountered in the management of such patients are highlighted.

Adult↗