Biomedical subjects
Publications and source records attributed to S D Jenkins.
A source of deterministic single photons is proposed and demonstrated by the application of a measurement-based feedback protocol to a heralded single-photon source consisting of an ensemble of cold rubidium atoms. Our source is stationary and produces a photoelectric detection record with sub-Poissonian statistics.
A quantum repeater at telecommunications wavelengths with long-lived atomic memory is proposed, and its critical elements are experimentally demonstrated using a cold atomic ensemble. Via atomic cascade emission, an entangled pair of 1.53 microm and 780 nm photons is generated. The former is ideal for long-distance quantum communication, and the latter is naturally suited for mapping to a long-lived atomic memory. Together with our previous demonstration of photonic-to-atomic qubit conversion, both of the essential elements for the proposed telecommunications quantum repeater have now been realized.
We report observations of entanglement of two remote atomic qubits, achieved by generating an entangled state of an atomic qubit and a single photon at site , transmitting the photon to site in an adjacent laboratory through an optical fiber, and converting the photon into an atomic qubit. Entanglement of the two remote atomic qubits is inferred by performing, locally, quantum state transfer of each of the atomic qubits onto a photonic qubit and subsequent measurement of polarization correlations in violation of the Bell inequality [EQUATION: SEE TEXT]. We experimentally determine [EQUATION: SEE TEXT]. Entanglement of two remote atomic qubits, each qubit consisting of two independent spin wave excitations, and reversible, coherent transfer of entanglement between matter and light represent important advances in quantum information science.
By time-dependent variation of a control field, both coherent and single-photon states of light are stored in, and retrieved from, a cold atomic gas. The efficiency of retrieval is studied as a function of the storage time in an applied magnetic field. A series of collapses and revivals is observed, in very good agreement with theoretical predictions. The observations are interpreted in terms of the time evolution of the collective excitation of atomic spin wave and light wave, known as the dark-state polariton.
An elementary quantum network operation involves storing a qubit state in an atomic quantum memory node, and then retrieving and transporting the information through a single photon excitation to a remote quantum memory node for further storage or analysis. Implementations of quantum network operations are thus conditioned on the ability to realize matter-to-light and/or light-to-matter quantum state mappings. Here we report the generation, transmission, storage and retrieval of single quanta using two remote atomic ensembles. A single photon is generated from a cold atomic ensemble at one site , and is directed to another site through 100 metres of optical fibre. The photon is then converted into a single collective atomic excitation using a dark-state polariton approach. After a programmable storage time, the atomic excitation is converted back into a single photon. This is demonstrated experimentally, for a storage time of 0.5 microseconds, by measurement of an anti-correlation parameter. Storage times exceeding ten microseconds are observed by intensity cross-correlation measurements. This storage period is two orders of magnitude longer than the time required to achieve conversion between photonic and atomic quanta. The controlled transfer of single quanta between remote quantum memories constitutes an important step towards distributed quantum networks.
The spectra of chi(2) spatial solitons are measured close to the soliton-formation threshold and show the presence of sidebands, shifted by 39 THz from the laser line. By comparing with the predictions of a quantum optical field model, solved numerically in the full (3 + 1)-dimensional space, it is claimed that the observed temporal instability of the spatial soliton is seeded by vacuum state fluctuations of the electromagnetic field.
We describe a new experimental approach to probabilistic atom-photon (signal) entanglement. Two qubit states are encoded as orthogonal collective spin excitations of an unpolarized atomic ensemble. After a programmable delay, the atomic excitation is converted into a photon (idler). Polarization states of both the signal and the idler are recorded and are found to be in violation of the Bell inequality. Atomic coherence times exceeding several microseconds are achieved by switching off all the trapping fields--including the quadrupole magnetic field of the magneto-optical trap--and zeroing out the residual ambient magnetic field.
BACKGROUND AND OBJECTIVE: Alexander disease is a slowly progressive CNS disorder that most commonly occurs in children. Until recently, the diagnosis could only be established by the histologic finding of Rosenthal fibers in brain specimens. Mutations in the glial fibrillary acidic protein (GFAP) gene have now been shown in a number of biopsy- or autopsy-proven patients with Alexander disease. A prospective study on patients suspected to have Alexander disease was conducted to determine the extent to which clinical and MRI criteria could accurately diagnose affected individuals, using GFAP gene sequencing as the confirmatory assay. METHODS: Patients who showed MRI white matter abnormalities consistent with Alexander disease, unremarkable family history, normal karyotype, and normal metabolic screening were included in this study. Genomic DNA from patients was screened for mutations in the entire coding region, including the exon-intron boundaries, of the GFAP gene. RESULTS: Twelve of 13 patients (approximately 90%) were found to have mutations in GFAP. Seven of those 12 patients presented in infancy with seizures and megalencephaly. Five were juvenile-onset patients with more variable symptoms. Two patients in the latter group were asymptomatic or minimally affected at the time of their initial MRI scan. The mutations were distributed throughout the gene, and all involved sporadic single amino acid heterozygous changes that changed the charge of the mutant protein. Four of the nine changes were novel mutations. CONCLUSIONS: In symptomatic and asymptomatic patients with a predominantly frontal leukoencephalopathy by MRI, GFAP gene mutation analysis should be included in the initial diagnostic evaluation process for Alexander disease.
Preliminary results indicate that a new laser Doppler flowmeter is more easily understood by nursing personnel than other laser Doppler units currently available. This monitor has demonstrated its capability in identifying and predicting tissue ischemia before clinically determined failure. Further evaluation of the device is warranted to define its use more clearly in the clinical setting.
A large abdominal wall hernia, not amenable to primary closure, may require insertion of a prosthesis. The ideal prosthesis maintains strength, is incorporated by surrounding tissues, and does not stimulate adhesions. These qualities vary among available synthetic prostheses. We tested tensile strength, bursting strength, and adhesion formation in response to six materials used in repair of abdominal wall hernias. Adult Sprague-Dawley rats (196) were randomly divided into a control group and six experimental groups. A 4 by 4 cm full-thickness resection of abdominal wall was closed with patches of polypropylene mesh (Marlex), polyglactin 910 mesh (Vicryl), expanded polytetrafluoroethylene (Gore-tex), Dacron-reinforced silicone rubber (Silastic), preserved human dura (PHD), or polypropylene mesh overlying gelatin film (Marlex and Gelfilm, respectively). In controls the 4 cm longitudinal full-thickness incisions were closed primarily. Seven rats randomly selected from each group were sacrificed after 1, 2, 4, and 8 weeks; bursting and tensile strength (tensiometer) and adhesion formation were assessed. There were no differences in bursting strength among the experimental groups at each testing period. Although bursting strength increased linearly with time it was significantly weaker than in controls at 1 and 8 weeks (P less than 0.05). Tensiometric data were inconclusive due to wide variability within the experimental groups. Adhesion formation was moderate to maximal at all evaluation periods for Marlex and Gore-tex. Early adhesion formation was minimal to moderate for both PHD and Vicryl, but later increased with PHD and decreased with Vicryl as this prosthesis was absorbed. No adhesions formed with Marlex and Gelfilm until the gelatin dissolved (1 week), after which the adhesion response was similar to that with Marlex alone. No adhesions formed after Silastic implantation, but graft extrusion and evisceration were common (75%). Controls had no adhesions at all evaluation periods. Wound strength was similar for all prosthetic materials. Absorbable prosthetic Vicryl provided the best long-term protection against adhesions.
The intimate association observed between osteoclasts and bone has suggested that these cells may be adherent to the bony surface. We investigated this cell-surface relationship in parathyroid hormone-stimulated bone explants following applications of biophysically-induced cell detachment forces. Bone surfaces adjacent to disrupted osteoclasts were examined with transmission electron microscopy for the presence of residual cell membrane elements. Results of this study provide evidence for the adherence of osteoclasts to bony surfaces and implicate elements of both clear zone and ruffled border as cell-membrane bonded sites.
Alternative pathway activity of human serum was titrated by use of unsensitized rabbit erythrocytes (RE). Under the conditions of the assay, the von Krogh equation could be used to relate the proportion of RE lysed to the level of alternative pathway activity. The use of a 50% hemolytic endpoint provided maximum sensitivity in the assay. The 50% hemolytic endpoint could be calculated from a single measurement in the region of 20% to 80% lysis or RE. Factor B was required for lysis of RE in the test, but neither C2 nor C8 was limiting under the conditions of the assay. Alternative pathway activities of three sera with abnormal IgG levels were in the normal range, but normal serum absorbed with RE at 0 C before testing had diminished lytic activity with the test. Lysis of RE in acute-phase sera of 16 patients who had bacteremic pneumococcal pneumonia was significantly below normal (P < 0.01). Results with Re lysis in these patients correlated well with levels of Factor B that were measured immunochemically and with consumption of whole complement by zymosan.
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