A quantum delayed choice experiment

Quantum systems exhibit particle-like or wave-like behaviour depending on the experimental apparatus they are confronted by. This wave-particle duality is at the heart of quantum mechanics, and is fully captured in Wheeler's famous delayed choice gedanken experiment. In this variant of the double slit experiment, the observer chooses to test either the particle or wave nature of a photon after it has passed through the slits. Here we report on a quantum delayed choice experiment, based on a quantum controlled beam-splitter, in which both particle and wave behaviours can be investigated simultaneously. The genuinely quantum nature of the photon's behaviour is tested via a Bell inequality, which here replaces the delayed choice of the observer. We observe strong Bell inequality violations, thus showing that no model in which the photon knows in advance what type of experiment it will be confronted by, hence behaving either as a particle or as wave, can account for the experimental data

On the experimental verification of quantum complexity in linear optics

The first quantum technologies to solve computational problems that are beyond the capabilities of classical computers are likely to be devices that exploit characteristics inherent to a particular physical system, to tackle a bespoke problem suited to those characteristics. Evidence implies that the detection of ensembles of photons, which have propagated through a linear optical circuit, is equivalent to sampling from a probability distribution that is intractable to classical simulation. However, it is probable that the complexity of this type of sampling problem means that its solution is classically unverifiable within a feasible number of trials, and the task of establishing correct operation becomes one of gathering sufficiently convincing circumstantial evidence. Here, we develop scalable methods to experimentally establish correct operation for this class of sampling algorithm, which we implement with two different types of optical circuits for 3, 4, and 5 photons, on Hilbert spaces of up to 50,000 dimensions. With only a small number of trials, we establish a confidence >99% that we are not sampling from a uniform distribution or a classical distribution, and we demonstrate a unitary specific witness that functions robustly for small amounts of data. Like the algorithmic operations they endorse, our methods exploit the characteristics native to the quantum system in question. Here we observe and make an application of a "bosonic clouding" phenomenon, interesting in its own right, where photons are found in local groups of modes superposed across two locations. Our broad approach is likely to be practical for all architectures for quantum technologies where formal verification methods for quantum algorithms are either intractable or unknown.Comment: Comments welcom

Quantum teleportation on a photonic chip

Quantum teleportation is a fundamental concept in quantum physics which now finds important applications at the heart of quantum technology including quantum relays, quantum repeaters and linear optics quantum computing (LOQC). Photonic implementations have largely focussed on achieving long distance teleportation due to its suitability for decoherence-free communication. Teleportation also plays a vital role in the scalability of photonic quantum computing, for which large linear optical networks will likely require an integrated architecture. Here we report the first demonstration of quantum teleportation in which all key parts - entanglement preparation, Bell-state analysis and quantum state tomography - are performed on a reconfigurable integrated photonic chip. We also show that a novel element-wise characterisation method is critical to mitigate component errors, a key technique which will become increasingly important as integrated circuits reach higher complexities necessary for quantum enhanced operation.Comment: Originally submitted version - refer to online journal for accepted manuscript; Nature Photonics (2014

Testing foundations of quantum mechanics with photons

The foundational ideas of quantum mechanics continue to give rise to counterintuitive theories and physical effects that are in conflict with a classical description of Nature. Experiments with light at the single photon level have historically been at the forefront of tests of fundamental quantum theory and new developments in photonics engineering continue to enable new experiments. Here we review recent photonic experiments to test two foundational themes in quantum mechanics: wave-particle duality, central to recent complementarity and delayed-choice experiments; and Bell nonlocality where recent theoretical and technological advances have allowed all controversial loopholes to be separately addressed in different photonics experiments.Comment: 10 pages, 5 figures, published as a Nature Physics Insight review articl

At the coalface and the cutting edge: general practitioners’ accounts of the rewards of engaging with HIV medicine

The interviews we conducted with GPs suggest that an engagement with HIV medicine enables clinicians to develop strong and long-term relationships with and expertise about the care needs of people living with HIV ‘at the coalface’, while also feeling connected with a broader network of medical practitioners and other professionals concerned with and contributing to the ever-changing world of science: ‘the cutting edge’. The general practice HIV prescriber is being modelled here as the interface between these two worlds, offering a rewarding opportunity for general practitioners to feel intimately connected to both community needs and scientific change

En busca de la ciudad sostenible

No deja de sorprender la capacidad de aguante que hemos generado los habitantes de grandes ciudades en Colombia. La cultura urbana, repleta de manifestaciones de “aguante, ha permitido de manera afortunada, introducir en el “homo colombianus” una especie de coraza, como el caparazón de una tortuga para guerrear y defenderse de los ataques frontales del medio ambiente urbano

Multipartite entanglement analysis from random correlations

Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.Ministry of Education (MOE)Published versionWe thank Otfried Gühne, Felix Huber, and Nikolai Wyderka for fruitful discussions. This research was supported by the DFG (Germany) and NCN (Poland) within the joint funding initiative “Beethoven 2” (2016/23/G/ST2/04273, 381445721), and by the DFG under Germany’s Excellence Strategy EXC-2111 390814868. We acknowledge the Singapore Ministry of Education Academic Research Fund Tier 2, Project No. MOE2015-T2-2-034. W.L. acknowledges partial support from the Foundation for Polish Science (IRAP project ICTQT, Contract No. 2018/MAB/5, cofinanced by EU via Smart Growth Operational Programme). T.P. is supported by the Polish National Agency for Academic Exchange NAWA Project No. PPN/PPO/2018/1/00007/U/00001. J.D. and L.K. acknowledge support from the PhD programs IMPRS-QST and ExQM, respectively

Vitamin D status and its predictive factors in pregnancy in 2 Australian populations

High prevalence rates of suboptimal vitamin D levels have been observed in women who are not considered ‘at risk’. The effect of behavioural factors such as sun exposure, attire, sunscreen use and vitamin D supplementation on vitamin D levels in pregnancy is unknown. The aim of this study was to determine prevalence and predictive factors of suboptimal vitamin D levels in 2 antenatal clinics in Australia - Campbelltown, NSW and Canberra, ACT. A cross-sectional study of pregnant women was performed with a survey of demographic and behavioural factors and a mid-pregnancy determination of maternal vitamin D levels. The prevalence of vitamin D deficiency (≤25 nmol/L) and insufficiency (26-50 nmol/L) was 35% in Canberra (n = 100) and 25.7% in Campbelltown (n = 101). The majority of participants with suboptimal D levels had vitamin D insufficiency. Among the vitamin D-deficient women, 38% were Caucasian. Skin exposure was the main behavioural determinant of vitamin D level in pregnancy in univariate analysis. Using pooled data ethnicity, season, BMI and use of vitamin D supplements were the main predictive factors of suboptimal vitamin D. Vitamin D supplementation at 500 IU/day was inadequate to prevent insufficiency. Behavioural factors were not as predictive as ethnicity, season and BMI. As most participants had one of the predictive risk factors for suboptimal vitamin D, a case could be made for universal supplementation with a higher dose of vitamin D in pregnancy and continued targeted screening of the women at highest risk of vitamin D deficiency

An Economic Model for Estimating Trial Costs with an Application to Placebo Surgery Trials

Background and Objective: Waste in clinical trials remains rife. We developed an economic model to predict the cost of trials based on input costs, duration, power, number of sites, recruitment eligibility and consenting rates. Methods: We parameterised the model for three proxy placebo-controlled surgical trials using data from a systematic review, a bespoke cost survey, and from the literature. We used the model to compare target and actual trial performance for (i) a trial that was completed on time but with more sites, (ii) a trial that completed after a time extension, and (iii) an incomplete trial. Results: Successful trials more accurately anticipated the true recruitment rate that they achieved and those that overestimated this were most likely to fail. The costs of overestimating recruitment rates were dramatic: all proxy trials had significantly higher costs than planned, with additional funding of at least AUD$600,000 (50$2 million (260% above budget) for incomplete trials. Conclusions: This model shows the trade-offs between time and cost, or both, when recruitment is lower than anticipated. Greater consideration is needed to improve trial planning, reviewing, and funding of these trials to avoid costly overruns and incomplete trials