Measuring the Joint Spectral Mode of Photon Pairs Using Intensity Interferometry.

The ability to manipulate and measure the time-frequency structure of quantum light is useful for information processing and metrology. Measuring this structure is also important when developing quantum light sources with high modal purity that can interfere with other independent sources. Here, we present and experimentally demonstrate a scheme based on intensity interferometry to measure the joint spectral mode of photon pairs produced by spontaneous parametric down-conversion. We observe correlations in the spectral phase of the photons due to chirp in the pump. We show that our scheme can be combined with stimulated emission tomography to quickly measure their mode using bright classical light. Our scheme does not require phase stability, nonlinearities, or spectral shaping and thus is an experimentally simple way of measuring the modal structure of quantum light.

Single-shot discrimination of coherent states beyond the standard quantum limit.

The discrimination of coherent states is a key task in optical communication and quantum key distribution protocols. In this work, we use a photon-number-resolving detector, the transition-edge sensor, to discriminate binary-phase-shifted coherent states at a telecom wavelength. Owing to its dynamic range and high efficiency, we achieve a bit error probability that unconditionally exceeds the standard quantum limit (SQL) by up to 7.7 dB. The improvement to the SQL persists for signals containing up to approximately seven photons on average and is achieved in a single shot (i.e., without measurement feedback), thus making our approach compatible with larger bandwidths.

Quantum-enhanced interferometry with large heralded photon-number states.

Quantum phenomena such as entanglement can improve fundamental limits on the sensitivity of a measurement probe. In optical interferometry, a probe consisting of N entangled photons provides up to a N enhancement in phase sensitivity compared to a classical probe of the same energy. Here, we employ high-gain parametric down-conversion sources and photon-number-resolving detectors to perform interferometry with heralded quantum probes of sizes up to N = 8 (i.e. measuring up to 16-photon coincidences). Our probes are created by injecting heralded photon-number states into an interferometer, and in principle provide quantum-enhanced phase sensitivity even in the presence of significant optical loss. Our work paves the way towards quantum-enhanced interferometry using large entangled photonic states.

Influence of early-life nutritional stress on songbird memory formation.

In birds, vocal learning enables the production of sexually selected complex songs, dialects and song copy matching. But stressful conditions during development have been shown to affect song production and complexity, mediated by changes in neural development. However, to date, no studies have tested whether early-life stress affects the neural processes underlying vocal learning, in contrast to song production. Here, we hypothesized that developmental stress alters auditory memory formation and neural processing of song stimuli. We experimentally stressed male nestling zebra finches and, in two separate experiments, tested their neural responses to song playbacks as adults, using either immediate early gene (IEG) expression or electrophysiological response. Once adult, nutritionally stressed males exhibited a reduced response to tutor song playback, as demonstrated by reduced expressions of two IEGs (Arc and ZENK) and reduced neuronal response, in both the caudomedial nidopallium (NCM) and mesopallium (CMM). Furthermore, nutritionally stressed males also showed impaired neuronal memory for novel songs heard in adulthood. These findings demonstrate, for the first time, that developmental conditions affect auditory memories that subserve vocal learning. Although the fitness consequences of such memory impairments remain to be determined, this study highlights the lasting impact early-life experiences can have on cognitive abilities.

Shape-preserving and unidirectional frequency conversion by four-wave mixing.

In this work, we investigate the properties of four-wave mixing Bragg scattering driven by orthogonally polarized pumps in a birefringent waveguide. This configuration enables a large signal conversion bandwidth, and allows strongly unidirectional frequency conversion as undesired Bragg-scattering processes are suppressed by waveguide birefringence. Moreover, we show that this form of Bragg scattering preserves the (arbitrary) signal pulse shape, even when driven by pulsed pumps.

Indistinguishable heralded single photon generation via relative temporal multiplexing of two sources.

Generating N single photons simultaneously is a formidable challenge due to the lack of deterministic single photon sources. Recent work [New J. Phys. 19, 063013 (2017] has proposed a relative multiplexing scheme that can enhance the N single photons probability with a minimum of active switching resources. We experimentally demonstrate relative temporal multiplexing on two photon sources with a 90% additional enhancement over the standard temporal multiplexing scheme demonstrated previously. 88 ± 11% visibility of Hong-Ou-Mandel quantum interference verifies the indistinguishability of the heralded single photons after the synchronization. This proof-of-principle demonstration points out the potential significance of the relative multiplexing scheme for large-scale photonic quantum information processing.

Experimental verification of multipartite entanglement in quantum networks.

Multipartite entangled states are a fundamental resource for a wide range of quantum information processing tasks. In particular, in quantum networks, it is essential for the parties involved to be able to verify if entanglement is present before they carry out a given distributed task. Here we design and experimentally demonstrate a protocol that allows any party in a network to check if a source is distributing a genuinely multipartite entangled state, even in the presence of untrusted parties. The protocol remains secure against dishonest behaviour of the source and other parties, including the use of system imperfections to their advantage. We demonstrate the verification protocol in a three- and four-party setting using polarization-entangled photons, highlighting its potential for realistic photonic quantum communication and networking applications.

Histopathology of the Retina from a Three Year-Old Suspected to Have Joubert Syndrome.

PURPOSE: To define the retinal pathology in a 3 year-old eye donor who died from complications of an undiagnosed genetic syndrome. METHODS: Eyes were fixed and analyzed using macroscopic fundus photography (MF), confocal scanning laser ophthalmoscopy (cSLO) and spectral-domain optical coherence tomography (SD-OCT). Small areas from the perifovea and periphery were processed for histology and indirect immunofluorescence, using antibodies specific to retinal proteins such as rhodopsin, cone arrestin, RPE65 and others. Available medical records were also reviewed. RESULTS: With all three imaging modalities, the affected donor's eyes lacked the distinct morphological detail typically observed with these techniques in postmortem control eyes. MF images showed a "photonegative effect" due to a hypopigmented macula relative to a hyperpigmented retinal background. cSLO imaging demonstrated a weak autofuorescence signal that was largely devoid of the usual retinal structures compared to the control. SD-OCT suggested disorganization of the affected retina, absence of a photoreceptor layer, and degeneration of the choroid in the macular area. Histologic findings indicated a highly disorganized photoreceptor layer in the macula and periphery. The RPE layer displayed thinning in some regions of the periphery and decreased pigmentation in most areas. Rods and cones were significantly reduced in the affected retina but a few cones were detected in the perifovea. Centrin-2 labeling was mostly absent from the connecting cilium of the photoreceptor cells. Medical record review pointed to a possible clinical diagnosis of Joubert syndrome. CONCLUSIONS: The retinal degenerative findings, and absence of centrin-2 labeling are compatible with the expected retinal phenotype in patients with Joubert syndrome.

Experimental demonstration of graph-state quantum secret sharing.

Quantum communication and computing offer many new opportunities for information processing in a connected world. Networks using quantum resources with tailor-made entanglement structures have been proposed for a variety of tasks, including distributing, sharing and processing information. Recently, a class of states known as graph states has emerged, providing versatile quantum resources for such networking tasks. Here we report an experimental demonstration of graph state-based quantum secret sharing--an important primitive for a quantum network with applications ranging from secure money transfer to multiparty quantum computation. We use an all-optical setup, encoding quantum information into photons representing a five-qubit graph state. We find that one can reliably encode, distribute and share quantum information amongst four parties, with various access structures based on the complex connectivity of the graph. Our results show that graph states are a promising approach for realising sophisticated multi-layered communication protocols in quantum networks.

Experimental realization of a one-way quantum computer algorithm solving Simon's problem.

We report an experimental demonstration of a one-way implementation of a quantum algorithm solving Simon's problem-a black-box period-finding problem that has an exponential gap between the classical and quantum runtime. Using an all-optical setup and modifying the bases of single-qubit measurements on a five-qubit cluster state, key representative functions of the logical two-qubit version's black box can be queried and solved. To the best of our knowledge, this work represents the first experimental realization of the quantum algorithm solving Simon's problem. The experimental results are in excellent agreement with the theoretical model, demonstrating the successful performance of the algorithm. With a view to scaling up to larger numbers of qubits, we analyze the resource requirements for an n-qubit version. This work helps highlight how one-way quantum computing provides a practical route to experimentally investigating the quantum-classical gap in the query complexity model.

Experimental demonstration of a graph state quantum error-correction code.

Scalable quantum computing and communication requires the protection of quantum information from the detrimental effects of decoherence and noise. Previous work tackling this problem has relied on the original circuit model for quantum computing. However, recently a family of entangled resources known as graph states has emerged as a versatile alternative for protecting quantum information. Depending on the graph's structure, errors can be detected and corrected in an efficient way using measurement-based techniques. Here we report an experimental demonstration of error correction using a graph state code. We use an all-optical setup to encode quantum information into photons representing a four-qubit graph state. We are able to reliably detect errors and correct against qubit loss. The graph we realize is setup independent, thus it could be employed in other physical settings. Our results show that graph state codes are a promising approach for achieving scalable quantum information processing.

An extended role for CT in the emergency diagnosis of malignant spinal cord compression.

AIM: To evaluate the usefulness of computed tomography (CT) for triaging between urgent transfer to a neurosurgical unit and delayed magnetic resonance imaging (MRI) in the local hospital. MATERIALS AND METHODS: Radiologists blinded to the MRI findings scored CT images from 1-5 using a novel grading system based on the degree of cord compression observed in 44 patients. Seventy separate levels were scored. The observers' CT scores were compared with the MRI findings. All scoring radiologists were specialist registrars at different stages of training. RESULTS: Agreement between CT and MRI scores for metastatic spinal cord compression (MSCC) were high with Cohen's weighted Kappa score 0.70 (p<0.001, 95% CI 0.65 to 0.75). CT has a sensitivity of 89% and specificity of 92% for MSCC. Half the false-positive and false-negative results came from a single junior radiologist who would not normally report CT or MRI studies unsupervised. The best CT-MRI agreement was from the most senior trainee radiologist. CONCLUSIONS: Spinal findings on routine staging whole-body CT combined with clinical findings are sufficient to determine which patients with MSCC can safely wait for MRI the next working day at the local hospital and those who need emergency transfer to a neurosurgical unit for MRI and possible surgical decompression.

Increased brain edema in aqp4-null mice in an experimental model of subarachnoid hemorrhage.

We investigated the role of the glial water channel protein aquaporin-4 in brain edema in a mouse model of subarachnoid hemorrhage in which 30 microl of blood was injected into the basal cisterns. Brain water content, intracranial pressure and neurological score were compared in wildtype and aquaporin-4 null mice. We also measured blood-brain barrier permeability, and the osmotic permeability of the glia limitans, one of the routes of edema elimination. Wildtype and aquaporin-4 null mice had comparable baseline brain water content, intracranial pressure and neurological score. At 6 h after blood injection, aquaporin-4 null mice developed more brain swelling than wildtype mice. Brain water content increased by 1.5+/-0.1% vs. 0.5+/-0.2% (Mean+/-Standard Error, P<0.0005) and intracranial pressure by 36+/-5 vs. 21+/-3 mm Hg (P<0.05) above pre-injection baseline, and neurological score was worse at 18.0 vs. 24.5 (median, P<0.05), respectively. Although subarachnoid hemorrhage produced comparable increases in blood-brain barrier permeability in wildtype and aquaporin-4 null mice, aquaporin-4 null mice had a twofold reduction in glia limitans osmotic permeability. We conclude that aquaporin-4 null mice manifest increased brain edema following subarachnoid hemorrhage as a consequence of reduced elimination of excess brain water.

Pattern recognition of MRSI data shows regions of glioma growth that agree with DTI markers of brain tumor infiltration.

Gliomas are the most common primary brain tumors and the majority are highly malignant, with one of the worst prognoses for patients. Gliomas are characterized by invasive growth into normal brain tissue that makes complete surgical resection and accurate radiotherapy planning extremely difficult. We have performed independent component analysis of magnetic resonance spectroscopy imaging data from human gliomas to segment brain tissue into tumor core, tumor infiltration, and normal brain, with confirmation by diffusion tensor imaging analysis. Our data are consistent with previous studies that compared anomalies in isotropic and anisotropic diffusion images to determine regions of potential glioma infiltration. We show that coefficients of independent components can be used to create colored images for easy visual identification of regions of infiltrative tumor growth.

Improved outcome after lumbar microdiscectomy in patients shown their excised disc fragments: a prospective, double blind, randomised, controlled trial.

BACKGROUND: Lumbar microdiscectomy (LMD) is a commonly performed neurosurgical procedure. We set up a prospective, double blind, randomised, controlled trial to test the hypothesis that presenting the removed disc material to patients after LMD improves patient outcome. METHODS: Adult patients undergoing LMD for radiculopathy caused by a prolapsed intervertebral disc were randomised into one of two groups, termed experimental and control. Patients in the experimental group were given their removed disc fragments whereas patients in the control group were not. Patients were unaware of the trial hypothesis and investigators were blinded to patient group allocation. Outcome was assessed between 3 and 6 months after LMD. Primary outcome measures were the degree of improvement in sciatica and back pain reported by the patients. Secondary outcome measures were the degree of improvement in leg weakness, paraesthesia, numbness, walking distance and use of analgesia reported by the patients. RESULTS: Data from 38 patients in the experimental group and 36 patients in the control group were analysed. The two groups were matched for age, sex and preoperative symptoms. More patients in the experimental compared with the control group reported improvements in leg pain (91.5 vs 80.4%; p<0.05), back pain (86.1 vs 75.0%; p<0.05), limb weakness (90.5 vs 56.3%; p<0.02), paraesthesia (88 vs 61.9%; p<0.05) and reduced analgesic use (92.1 vs 69.4%; p<0.02) than preoperatively. CONCLUSION: Presentation of excised disc fragments is a cheap and effective way to improve outcome after LMD.

AQP4 gene deletion in mice does not alter blood-brain barrier integrity or brain morphology.

The glial cell water channel aquaporin-4 (AQP4) plays an important role in brain edema, astrocyte migration, and neuronal excitability. Zhou et al. [Zhou J, Kong H, Hua X, Xiao M, Ding J, Hu G (2008) Altered blood-brain barrier integrity in adult aquaporin-4 knockout mice. Neuroreport 19:1-5] recently reported that AQP4 deletion significantly altered blood-brain barrier integrity and glial fibrillary acidic protein (GFAP) immunoreactivity in their AQP4 null mice. Here we describe a detailed characterization of baseline brain properties in our AQP4 null mice, including gross appearance, neuronal, astrocyte and oligodendrocyte characteristics, and blood-brain barrier integrity. Gross anatomical measurements included estimates of brain and ventricle size. Neurons, astrocytes and oligodendrocytes were assessed using the neuronal nuclear marker NeuN, the astrocyte marker GFAP, and the myelin stain Luxol Fast Blue. The blood-brain barrier was studied by electron microscopy and the horseradish peroxidase extravasation technique. There were no differences in brain and ventricle sizes between wild type and AQP4 null mice, nor were there differences in the cerebral cortical density of NeuN positive nuclei, perimicrovessel and glia limitans GFAP immunoreactivity, or the thickness and myelination of the corpus callosum. The ultrastructure of microvessels in the frontal cortex and caudate nucleus of wild type vs. AQP4 null mice was indistinguishable, with features including intact endothelial tight junctions, absence of perimicrovessel astrocyte foot process edema, and absence of horseradish peroxidase extravasation. In contrast to the report by Zhou et al. (2008), our data show that AQP4 deletion in mice does not produce major structural abnormalities in the brain.

Taurine: a potential marker of apoptosis in gliomas.

New cancer therapies are being developed that trigger tumour apoptosis and an in vivo method of apoptotic detection and early treatment response would be of great value. Magnetic resonance spectroscopy (MRS) can determine the tumour biochemical profile in vivo, and we have investigated whether a specific spectroscopic signature exists for apoptosis in human astrocytomas. High-resolution magic angle spinning (HRMAS) (1)H MRS provided detailed (1)H spectra of brain tumour biopsies for direct correlation with histopathology. Metabolites, mobile lipids and macromolecules were quantified from presaturation HRMAS (1)H spectra acquired from 41 biopsies of grades II (n=8), III (n=3) and IV (n=30) astrocytomas. Subsequently, TUNEL and H&E staining provided quantification of apoptosis, cell density and necrosis. Taurine was found to significantly correlate with apoptotic cell density (TUNEL) in both non-necrotic (R=0.727, P=0.003) and necrotic (R=0.626, P=0.0005) biopsies. However, the ca 2.8 p.p.m. polyunsaturated fatty acid peak, observed in other studies as a marker of apoptosis, correlated only in non-necrotic biopsies (R=0.705, P<0.005). We suggest that the taurine (1)H MRS signal in astrocytomas may be a robust apoptotic biomarker that is independent of tumour necrotic status.

Current neurosurgical trainees' perception of the European Working Time Directive and shift work.

The introduction of the shift system in response to the European Working Time Directive has had an enormous impact on the running of neurosurgical units in the UK. This study seeks to establish what provisions are currently in place for out of hours cover and what has been the effect of the introduction of shifts in three main areas: patient safety, training and 'work/life balance'. The on-call registrar at each UK neurosurgical unit was contacted by telephone. Data regarding current emergency provision were sought. Registrars who had worked both on-calls and the shift system during their career as a neurosurgical registrar were asked to make a comparison. Data were collected from all 33 UK units. Twenty-two still use a traditional 24-h on-call system. Twenty-one on-call rotas were classed as non-resident although 12/21 of those officially on non-resident rotas were in fact resident whilst on call. Twenty-two registrars had worked both systems as a neurosurgical registrar. Twenty-one (95.45%) felt that traditional on-calls gave better clinical exposure. Twenty-one (95.45%) felt that on-calls allowed the provision of better patient care. Nineteen (86.36%) felt that on-calls were safer. Thirteen (59.09%) reported that they were more tired when doing shift work than on-calls. Fourteen (63.63%) found that the on-call system gives more useful spare time and more time to deal with family commitments. Current neurosurgery registrars feel the shift system is less safe, harmful to training and worse in terms of work/life balance. More than one-third of units are claiming to have non-resident on-call systems in order to appear compliant with EWTD when registrars are in fact resident.

Survival of patients with glioblastoma multiforme has not improved between 1993 and 2004: analysis of 625 cases.

Glioblastoma is the most common primary brain tumour. The aim of this study was to determine trends in survival over a 12-year period. Survival data were collected retrospectively for 625 patients who had surgery for histologically-confirmed glioblastoma between 1993 and 2004 in a single centre. Data including age, sex, preoperative Karnofsky performance score, tumour site, date of surgery, and type of surgical and adjuvant treatment were collected. Overall median survival was 189 days; there was no significant change in survival over 12 years. Multivariate analysis identified the following independent positive prognostic factors: age <60 years (p < 0.0005), Karnofsky score > or = 70 (p < 0.0001), tumour debulking, rather than biopsy (p < 0.001), right-sided lesion (p < 0.05), unilateral tumour (p < 0.05) and radiotherapy (p < 0.0001). Despite neurosurgical advances, the survival of patients with glioblastoma has not changed for more than a decade. Although, overall, glioblastoma has a short survival, our data show that individual patient survival is heterogeneous.