107 research outputs found
Hardy's paradox and violation of a state-independent Bell inequality in time
Tests such as Bell's inequality and Hardy's paradox show that joint
probabilities and correlations between distant particles in quantum mechanics
are inconsistent with local realistic theories. Here we experimentally
demonstrate these concepts in the time domain, using a photonic entangling gate
to perform nondestructive measurements on a single photon at different times.
We show that Hardy's paradox is much stronger in time and demonstrate the
violation of a temporal Bell inequality independent of the quantum state,
including for fully mixed states.Comment: Published Version, 4 pages, 3 figures. New, more boring titl
Entanglement-free certification of entangling gates
Not all quantum protocols require entanglement to outperform their classical
alternatives. The nonclassical correlations that lead to this quantum advantage
are conjectured to be captured by quantum discord. Here we demonstrate that
discord can be explicitly used as a resource: certifying untrusted entangling
gates without generating entanglement at any stage. We implement our protocol
in the single-photon regime, and show its success in the presence of high
levels of noise and imperfect gate operations. Our technique offers a practical
method for benchmarking entangling gates in physical architectures in which
only highly-mixed states are available.Comment: 5 pages, 2 figure
Mood instability : significance, definition and measurement
Mood instability is common, and an important feature of several psychiatric disorders. We discuss the definition and measurement of mood instability, and review its prevalence, characteristics, neurobiological correlates and clinical implications. We suggest that mood instability has underappreciated transdiagnostic potential as an investigational and therapeutic target
Enhancing quantum transport in a photonic network using controllable decoherence
Transport phenomena on a quantum scale appear in a variety of systems,
ranging from photosynthetic complexes to engineered quantum devices. It has
been predicted that the efficiency of quantum transport can be enhanced through
dynamic interaction between the system and a noisy environment. We report the
first experimental demonstration of such environment-assisted quantum
transport, using an engineered network of laser-written waveguides, with
relative energies and inter-waveguide couplings tailored to yield the desired
Hamiltonian. Controllable decoherence is simulated via broadening the bandwidth
of the input illumination, yielding a significant increase in transport
efficiency relative to the narrowband case. We show integrated optics to be
suitable for simulating specific target Hamiltonians as well as open quantum
systems with controllable loss and decoherence.Comment: 6 pages, 3 figure
Experimental simulation of closed timelike curves
Closed timelike curves are among the most controversial features of modern physics. As legitimate solutions to Einstein's field equations, they allow for time travel, which instinctively seems paradoxical. However, in the quantum regime these paradoxes can be resolved, leaving closed timelike curves consistent with relativity. The study of these systems therefore provides valuable insight into nonlinearities and the emergence of causal structures in quantum mechanics-essential for any formulation of a quantum theory of gravity. Here we experimentally simulate the nonlinear behaviour of a qubit interacting unitarily with an older version of itself, addressing some of the fascinating effects that arise in systems traversing a closed timelike curve. These include perfect discrimination of non-orthogonal states and, most intriguingly, the ability to distinguish nominally equivalent ways of preparing pure quantum states. Finally, we examine the dependence of these effects on the initial qubit state, the form of the unitary interaction and the influence of decoherence
Concepts of mental disorders in the United Kingdom : Similarities and differences between the lay public and psychiatrists
BACKGROUND: The lay public often conceptualise mental disorders in a different way to mental health professionals, and this can negatively impact on outcomes when in treatment. AIMS: This study explored which disorders the lay public are familiar with, which theoretical models they understand, which they endorse and how they compared to a sample of psychiatrists. METHODS: The Maudsley Attitude Questionnaire (MAQ), typically used to assess mental health professional's concepts of mental disorders, was adapted for use by a lay community sample (N = 160). The results were compared with a sample of psychiatrists (N = 76). RESULTS: The MAQ appeared to be accessible to the lay public, providing some interesting preliminary findings: in order, the lay sample reported having the best understanding of depression followed by generalised anxiety, schizophrenia and finally antisocial personality disorder. They best understood spiritualist, nihilist and social realist theoretical models of these disorders, but were most likely to endorse biological, behavioural and cognitive models. The lay public were significantly more likely to endorse some models for certain disorders suggesting a nuanced understanding of the cause and likely cure, of various disorders. Ratings often differed significantly from the sample of psychiatrists who were relatively steadfast in their endorsement of the biological model. CONCLUSION: The adapted MAQ appeared accessible to the lay sample. Results suggest that the lay public are generally aligned with evidence-driven concepts of common disorders, but may not always understand or agree with how mental health professionals conceptualise them. The possible causes of these differences, future avenues for research and the implications for more collaborative, patient-clinician conceptualisations are discussed.Peer reviewedFinal Accepted Versio
Efficient demultiplexed single-photon source with a quantum dot coupled to a nanophotonic waveguide
Planar nanostructures allow near-ideal extraction of emission from a quantum
emitter embedded within, thereby realizing deterministic single-photon sources.
Such a source can be transformed into M single-photon sources by implementing
active temporal-to-spatial mode demultiplexing. We report on the realization of
such a demultiplexed source based on a quantum dot embedded in a nanophotonic
waveguide. Efficient outcoupling (>60%) from the waveguide into a single mode
optical fiber is obtained with high-efficiency grating couplers. As a
proof-of-concept, active demultiplexing into M=4 spatial channels is
demonstrated by the use of electro-optic modulators with an end-to-end
efficiency of >81% into single-mode fibers. Overall we demonstrate four-photon
coincidence rates of >1 Hz even under non-resonant excitation of the quantum
dot. The main limitation of the current source is the residual population of
other exciton transitions that corresponds to a finite preparation efficiency
of the desired transition. We quantitatively extract a preparation efficiency
of 15% using the second-order correlation function measurements. The experiment
highlights the applicability of planar nanostructures as efficient multiphoton
sources through temporal-to-spatial demultiplexing and lays out a clear path
way of how to scale up towards demonstrating quantum advantages with the
quantum dot sources.Comment: 5 pages, 3 figure
Delusional beliefs and reason giving
Delusions are often regarded as irrational beliefs, but their irrationality is not sufficient to explain what is pathological about them. In this paper we ask whether deluded subjects have the capacity to support the content of their delusions with reasons, that is, whether they can author their delusional states. The hypothesis that delusions are characterised by a failure of authorship, which is a dimension of self knowledge, deserves to be
empirically tested because (a) it has the potential to account for the distinction between endorsing a delusion and endorsing a framework belief; (b) it contributes to a
philosophical analysis of the relationship between rationality and self knowledge; and (c) it informs diagnosis and therapy in clinical psychiatry. However, authorship cannot provide a demarcation criterion between delusions and other irrational belief states
Prefrontal GABA levels, hippocampal resting perfusion and the risk of psychosis
This article was originally published under NPG’s License to Publish, but has now been made available under a [CC BY 4.0] license. The PDF and HTML versions of the paper have been modified accordingly.</p
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