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Violation of new Bell’s Inequalities in PRA

qoqi — Wed, 20 Mar 2013 14:34:41 +0000

A new paper, Experimental violation of three families of Bell’s Inequalities by Lydia Vermeyden, Madeleine Bonsma, Crystal Noel, John Donohue, Elie Wolfe, and Kevin Resch was just published in Physical Review A.

Abstract: Bell’s inequalities are important to our understanding of quantum foundations and critical to several quantum technologies. A recent work [ E. Wolfe and S. F. Yelin Phys. Rev. A 86 012123 (2012)] derived three parametrized families of two-particle, two-setting Bell inequalities. These inequalities are important as they theoretically explore a larger volume of allowed quantum correlations over local hidden-variable models than previous results [ A. Cabello Phys. Rev. A 72 012113 (2005)] by exploiting marginal, or single particle measurements. In this work we subject those predictions to experimental test using nonmaximally entangled photon pairs to optimize the expected violation. We find excellent agreement with the upper bounds predicted by quantum mechanics with violations of the limits imposed by local hidden-variable models as large as almost 30σ for the optimal parameters and a significant violation over a wide range of parameters.

Deny wins Dean of Science Award

qoqi — Wed, 01 Jun 2011 17:20:38 +0000

Deny Hamel has been awarded the 2011 University of Waterloo Dean of Science Award for his MSc thesis, Realization of novel entangled photon sources using periodically-poled materials. Congratulations Deny!

The Dean of Science Award is given in recognition of outstanding performance in the Master of Science program. One certificate will normally be awarded annually to a master’s student from each department in the Science faculty in recognition of creative research as presented in the student’s thesis.

Update: June 14, 2011. Deny received his award today from Terry McMahon, Dean of Science.

And here’s the proof…

Entanglement-assisted classical communication in PRL

qoqi — Mon, 14 Mar 2011 15:44:43 +0000

Our paper, Entanglement-assisted classical communication over a noisy classical channel, by Robert Prevedel, Yang Lu, Rainer Kaltenbaek, Will Matthews, and Kevin Resch was published today in Physical Review Letters. This article was chosen as a Editor’s Suggestion and selected for a Viewpoint in Physics entitled ‘Entangled in a dating game‘ by Mark Wilde (McGill University). It was also discussed in a Physics Update on the Physics Today website by Johanna Miller.

Abstract: We present and experimentally demonstrate a communication protocol that employs shared entanglement to reduce errors when sending a bit over a particular noisy classical channel. Specifically, it is shown that given a single use of this channel, one can transmit a bit with higher success probability when the sender and receiver share entanglement compared to the best possible strategy when they do not. The experiment is realized using polarization-entangled photon pairs, whose quantum correlations play a critical role in both the encoding and decoding of the classical message. Experimentally, we find that a bit can be successfully transmitted with probability 0.891±0.002, which is close to the theoretical maximum of (2+2^-1/2)/3≈0.902 and is significantly above the optimal classical strategy, which yields 5/6≈0.833.

Update April 1, 2011: A Search and Discovery article, Entanglement enhances classical communication, by Johanna Miller was published in Physics Today…today.

Entangled state discrimination results in PRA

qoqi — Fri, 29 Oct 2010 15:22:26 +0000

Our paper Minimum-error discrimination of entangled quantum states by Yang Lu, Nick Coish, Rainer Kaltenbaek, Deny Hamel, Sarah Croke, and Kevin Resch was published today in Physical Review A.

Abstract: Strategies to optimally discriminate between quantum states are critical in quantum technologies. We present an experimental demonstration of minimum-error discrimination between entangled states, encoded in the polarization of pairs of photons. Although the optimal measurement involves projection onto entangled states, we use a result of J. Walgate et al. [Phys. Rev. Lett. 85, 4972 (2000)] to design an optical implementation employing only local polarization measurements and feed-forward, which performs at the Helstrom bound. Our scheme can achieve perfect discrimination of orthogonal states and minimum-error discrimination of nonorthogonal states. Our experimental results show a definite advantage over schemes not using feed-forward.

Experimental Bound Entanglement in PRL

qoqi — Thu, 23 Sep 2010 15:00:22 +0000

Experimental Bound Entanglement in a Four-Photon State by Jonathan Lavoie, Rainer Kaltenbaek, Marco Piani, and Kevin Resch was published today in Physical Review Letters.

Bound entanglement is central to many exciting theoretical results in quantum information processing, but has thus far not been experimentally realized. In this work, we consider a one-parameter family of four-qubit Smolin states. We experimentally produce these states in the polarization of four optical photons produced from parametric down-conversion. Within a range of the parameter, we show that our states are entangled and undistillable, and thus bound entangled. Using these bound-entangled states we demonstrate entanglement unlocking.

An experimental 4-photon bound entangled state from a family of noisy Smolin states

Remote state preparation results published in PRA

qoqi — Fri, 29 Jan 2010 21:24:36 +0000

Our paper, Derivation and experimental test of fidelity benchmarks for remote preparation of arbitrary qubit states, was published in Physical Review A. This work was done in collaboration with Norbert Lütkenhaus at IQC.

Remote state preparation (RSP) is the act of preparing a quantum state at a remote location without actually transmitting the state itself. Using at most two classical bits and a single shared maximally entangled state, one can in theory remotely prepare any qubit state with certainty and with perfect fidelity. However, in any experimental implementation the average fidelity between the target and output states cannot be perfect. In order for an RSP experiment to demonstrate genuine quantum advantages, it must surpass the optimal threshold of a comparable classical protocol. Here we study the fidelity achievable by RSP protocols lacking shared entanglement and determine the optimal value for the average fidelity in several different cases. We implement an experimental scheme for deterministic remote preparation of arbitrary photon polarization qubits, preparing 178 different pure and mixed qubit states with an average fidelity of 0.995. Our experimentally achieved average fidelities surpass our derived classical thresholds whenever the classical protocol does not trivially allow for perfect RSP.

Classical thresholds and their violation in our experiment