Quantum states made to measure

Recent progress in manipulating quantum states of light and matter brings quantum-enhanced measurements closer to prospective applications. The current challenge is to make quantum metrologic strategies robust against imperfections.Comment: 4 pages, 3 figures, Commentary for Nature Photonic

Super-resolving phase measurements with a multi-photon entangled state

Using a linear optical elements and post-selection, we construct an entangled polarization state of three photons in the same spatial mode. This state is analogous to a ``photon-number path entangled state'' and can be used for super-resolving interferometry. Measuring a birefringent phase shift, we demonstrate two- and three-fold improvements in phase resolution.Comment: 4 pages, 3 figure

De Broglie Wavelength of a Nonlocal Four-Photon

Superposition is one of the most distinct features of quantum theory and has been demonstrated in numerous realizations of Young's classical double-slit interference experiment and its analogues. However, quantum entanglement - a significant coherent superposition in multiparticle systems - yields phenomena that are much richer and more interesting than anything that can be seen in a one-particle system. Among them, one important type of multi-particle experiments uses path-entangled number-states, which exhibit pure higher-order interference and allow novel applications in metrology and imaging such as quantum interferometry and spectroscopy with phase sensitivity at the Heisenberg limit or quantum lithography beyond the classical diffraction limit. Up to now, in optical implementations of such schemes lower-order interference effects would always decrease the overall performance at higher particle numbers. They have thus been limited to two photons. We overcome this limitation and demonstrate a linear-optics-based four-photon interferometer. Observation of a four-particle mode-entangled state is confirmed by interference fringes with a periodicity of one quarter of the single-photon wavelength. This scheme can readily be extended to arbitrary photon numbers and thus represents an important step towards realizable applications with entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200

Entanglement-free Heisenberg-limited phase estimation

Measurement underpins all quantitative science. A key example is the measurement of optical phase, used in length metrology and many other applications. Advances in precision measurement have consistently led to important scientific discoveries. At the fundamental level, measurement precision is limited by the number N of quantum resources (such as photons) that are used. Standard measurement schemes, using each resource independently, lead to a phase uncertainty that scales as 1/sqrt(N) - known as the standard quantum limit. However, it has long been conjectured that it should be possible to achieve a precision limited only by the Heisenberg uncertainty principle, dramatically improving the scaling to 1/N. It is commonly thought that achieving this improvement requires the use of exotic quantum entangled states, such as the NOON state. These states are extremely difficult to generate. Measurement schemes with counted photons or ions have been performed with N <= 6, but few have surpassed the standard quantum limit and none have shown Heisenberg-limited scaling. Here we demonstrate experimentally a Heisenberg-limited phase estimation procedure. We replace entangled input states with multiple applications of the phase shift on unentangled single-photon states. We generalize Kitaev's phase estimation algorithm using adaptive measurement theory to achieve a standard deviation scaling at the Heisenberg limit. For the largest number of resources used (N = 378), we estimate an unknown phase with a variance more than 10 dB below the standard quantum limit; achieving this variance would require more than 4,000 resources using standard interferometry. Our results represent a drastic reduction in the complexity of achieving quantum-enhanced measurement precision.Comment: Published in Nature. This is the final versio

Male Circumcision for HIV Prevention in High HIV Prevalence Settings: What Can Mathematical Modelling Contribute to Informed Decision Making?

Published versio

Rules of Engagement: Journalists’ attitudes to industry influence in health news reporting.

Health-related industries use a variety of methods to influence health news, including the formation and maintenance of direct relationships with journalists. These interactions have the potential to subvert news reporting such that it comes to serve the interests of industry in promoting their products, rather than the public interest in critical and accurate news and information. Here we report the findings of qualitative interviews conducted in Sydney, Australia, in which we examined journalists’ experiences of, and attitudes towards, their relationships with health-related industries. Participants’ belief in their ability to manage industry influence and their perceptions of what it means to be unduly influenced by industry raise important concerns relating to the psychology of influence and the realities of power relationships between industry and journalists. The analysis also indicates ways in which concerned academics and working journalists might establish more fruitful dialogue regarding the role of industry in health-related news and the extent to which increased regulation of journalist-industry relationships might be needed.NHMR

Experimental quantum-enhanced estimation of a lossy phase shift

When standard light sources are employed, the precision of the phase determination is limited by the shot noise. Quantum entanglement provides means to exceed this limit with the celebrated example of N00N states that saturate the ultimate Heisenberg limit on precision, but at the same time are extremely fragile to losses. In contrast, we provide experimental evidence that appropriately engineered quantum states outperform both standard and N00N states in the precision of phase estimation when losses are present.Comment: 5 page

Global health education: a pilot in trans-disciplinary, digital instruction

Background: The development of new global health academic programs provides unique opportunities to create innovative educational approaches within and across universities. Recent evidence suggests that digital media technologies may provide feasible and cost-effective alternatives to traditional classroom instruction; yet, many emerging global health academic programs lag behind in the utilization of modern technologies. Objective: We created an inter-departmental University of Southern California (USC) collaboration to develop and implement a course focused on digital media and global health. Design: Course curriculum was based on core tenants of modern education: multi-disciplinary, technologically advanced, learner-centered, and professional application of knowledge. Student and university evaluations were reviewed to qualitatively assess course satisfaction and educational outcomes. Results: &#x2018;New Media for Global Health&#x2019; ran for 18 weeks in the Spring 2012 semester with N=41 students (56.1% global health and 43.9% digital studies students). The course resulted in a number of high quality global health-related digital media products available at http://iml420.wordpress.com/. Challenges confronted at USC included administrative challenges related to co-teaching and frustration from students conditioned to a rigid system of teacher-led learning within a specific discipline. Quantitative and qualitative course evaluations reflected positive feedback for the course instructors and mixed reviews for the organization of the course. Conclusion: The development of innovative educational programs in global health requires on-going experimentation and information sharing across departments and universities. Digital media technologies may have implications for future efforts to improve global health education

Voluntary Medical Male Circumcision: Modeling the Impact and Cost of Expanding Male Circumcision for HIV Prevention in Eastern and Southern Africa

Emmanuel Njeuhmeli and colleagues estimate the impact and cost of scaling up adult medical male circumcision in 13 priority countries in eastern and southern Africa, finding that reaching 80% coverage and maintaining it until 2025 would avert 3.36 million new HIV infections