Prevedel, R., Hamel, D. R., Colbeck, R., Fisher, K., & Resch, K. J. (2011). Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement. Nat. Phys., 7(10), 757–761.
Abstract: Heisenberg's uncertainty principle provides a fundamental limitation on the ability of an observer holding classical information to predict the outcome when one of two measurements is performed on a quantum system. However, an observer with access to a particle (stored in a quantum memory) which is entangled with the system generally has a reduced uncertainty: indeed, if the particle and system are maximally entangled, the observer can perfectly predict the outcome of whichever measurement is chosen. This effect has recently been quantified in a new entropic uncertainty relation. Here we experimentally investigate this relation, showing its effectiveness as an efficient entanglement witness. We use entangled photon pairs, an optical delay line serving as a simple quantum memory and fast, active feed-forward. Our results quantitatively agree with the new uncertainty relation. Our technique acts as a witness for almost all entangled states in our experiment as we obtain lower uncertainties than would be possible without the entangled particle.
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Raussendorf, R. (2010). Quantum computing: Shaking up ground states. Nat. Phys., 6(11), 840–841.
Abstract: Measurement-based quantum computation with an Affleck-Kennedy-Lieb-Tasaki state is experimentally realized for the first time.
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Saffman, M. (2010). Quantum computing: A quantum telecom link. Nat. Phys., 6(11), 838–839.
Abstract: Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances.
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Saunders, D. J., Jones, S. J., Wiseman, H. M., & Pryde, G. J. (2010). Experimental EPR-steering using Bell-local states. Nat. Phys., 6(11), 845–849.
Abstract: The concept of `steering' was introduced in 1935 by Schrödinger as a generalization of the EPR (Einstein-Podolsky-Rosen) paradox. It has recently been formalized as a quantum-information task with arbitrary bipartite states and measurements, for which the existence of entanglement is necessary but not sufficient. Previous experiments in this area have been restricted to an approach that followed the original EPR argument in considering only two different measurement settings per side. Here we demonstrate experimentally that EPR-steering occurs for mixed entangled states that are Bell local (that is, that cannot possibly demonstrate Bell non-locality). Unlike the case of Bell inequalities, increasing the number of measurement settings beyond two-we use up to six-significantly increases the robustness of the EPR-steering phenomenon to noise.
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Shor, P. W. (2009). Quantum information theory: The bits don't add up. Nat. Phys., 5, 247–248.
Abstract: A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel.
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