Introduction

We are an experimental quantum optics group run by Kevin Resch, based in the Department of Physics & Astronomy and the Institute for Quantum Computing at the University of Waterloo.

Ultrafast entangled-photon demultiplexing in PRL

We have a new paper in Physical Review Letters entitled, Ultrafast Time-Division Demultiplexing of Polarization-Entangled Photons, by John Donohue, Jonathan Lavoie, and Kevin Resch.

Abstract: Maximizing the information transmission rate through quantum channels is essential for practical implementation of quantum communication. Time-division multiplexing is an approach for which the ultimate rate requires the ability to manipulate and detect single photons on ultrafast time scales while preserving their quantum correlations. Here we demonstrate the demultiplexing of a train of pulsed single photons using time-to-frequency conversion while preserving their polarization entanglement with a partner photon. Our technique converts a pulse train with 2.69 ps spacing to a frequency comb with 307 GHz spacing which may be resolved using diffraction techniques. Our work enables ultrafast multiplexing of quantum information with commercially available single-photon detectors.

mutiplexingconcept

Polarization entangled photon triplets in Nature Photonics

Check out our new paper in Nature Photonics entitled, Direct generation of three-photon polarizaton entanglement, by Deny R. Hamel, Lynden K. Shalm, Hannes Hübel, Aaron J. Miller, Francesco Marsili, Varun B. Verma, Richard P. Mirin, Sae Woo Nam, Kevin J. Resch, and Thomas Jennewein.

Abstract: Non-classical states of light are of fundamental importance for emerging quantum technologies. All optics experiments producing multi-qubit entangled states have until now relied on outcome post-selection, a procedure where only the measurement results corresponding to the desired state are considered. This method severely limits the usefulness of the resulting entangled states. Here, we show the direct production of polarization-entangled photon triplets by cascading two entangled downconversion processes. Detecting the triplets with high-efficiency superconducting nanowire single-photon detectors allows us to fully characterize them through quantum state tomography. We use our three-photon entangled state to demonstrate the ability to herald Bell states, a task that was not possible with previous three-photon states, and test local realism by violating the Mermin and Svetlichny inequalities. These results represent a significant breakthrough for entangled multi-photon state production by eliminating the constraints of outcome post-selection, providing a novel resource for optical quantum information processing.

Update Oct 18, 2014: Our article was discussed on physorg.com, sciencenews.orgphotonics.com, and the Popular Science website

Congratulations

…to John for being awarded the NSERC CSG-D scholarship!

…to Mike for winning the Dean of Science Award for his MSc thesis!

…to Megan for being awarded the NSERC Vanier scholarship and completing the MSc!

…to Lydia for completing the MSc!

Separating photon triplets to test quantum nonlocality

We have a new paper out (online) in Nature Photonics today entitled, Experimental three-photon quantum nonlocality under strict locality conditions, by Chris Erven, Evan Mayer-Scott, Kent Fisher, Jonathan Lavoie, Brendon Higgins, Zhizhong Yan, Chris Pugh, Jean-Phillipe Bourgoin, Robert Prevedel, Krister Shalm, Laura Richards, Nick Gigov, Raymond Laflamme, Gregor Weihs, Thomas Jennewein, and Kevin Resch.   This paper is the result of a great collaboration between three IQC groups and a former IQC faculty member, now at University of Innsbruck.

Abstract: Quantum correlations, often observed as violations of Bell inequalities, are critical to our understanding of the quantum world, with far-reaching technologicaland fundamental impact. Many tests of Bell inequalities have studied pairs of correlated particles. However, interest in multi-particle quantum correlations is driving the experimental frontier to test larger systems. All violations to date require supplementary assumptions that open results to loopholes, the closing of which is one of the most important challenges in quantum science. Seminal experiments have closed some loopholes, but no experiment has closed locality loopholes with three or more particles. Here, we close both the locality and freedom-of-choice loopholes by distributing three-photon Greenberger–Horne–Zeilinger entangled statesto independent observers. We measured a violation of Mermin’s inequalitywith parameter 2.77 ± 0.08, violating its classical bound by nine standard deviations. These results are a milestone in multi-party quantum communication and a significant advancement of the foundations of quantum mechanics.

Update April 16, 2014: Geoff Pryde discussed our work in a Nature Photonics News and Views article Entanglement à trois

Jean-Phillipe wins prestigious prize

Jean-Phillipe has won the 2013 NSERC André Hamer Postgraduate Prize.

The NSERC André Hamer Postgraduate Prizes are awarded to the most outstanding candidates in NSERC‘s master’s and doctoral scholarship competitions. Valued at $10,000 each, the prizes were established by Arthur McDonald, winner of the 2003 Gerhard Herzberg Canada Gold Medal for Science and Engineering, in memory of a very promising young scientist who passed away in 2003.

Congratulations Jean-Phillipe!

Citation on the NSERC website.

Rvbouvn dpnqvujoh po fodszqufe ebub

Our new paper, Quantum Computing on encrypted data, by Kent Fisher, Anne Broadbent, Krister Shalm, Zhizhong Yan, Jonathan Lavoie, Robert Prevedel, Thomas Jennewein, and Kevin Resch was published in Nature Communications.

Abstract: The ability to perform computations on encrypted data is a powerful tool for protecting privacy. Recently, protocols to achieve this on classical computing systems have been found. Here, we present an efficient solution to the quantum analogue of this problem that enables arbitrary quantum computations to be carried out on encrypted quantum data. We prove that an untrusted server can implement a universal set of quantum gates on encrypted quantum bits (qubits) without learning any information about the inputs, while the client, knowing the decryption key, can easily decrypt the results of the computation. We experimentally demonstrate, using single photons and linear optics, the encryption and decryption scheme on a set of gates sufficient for arbitrary quantum computations. As our protocol requires few extra resources compared with other schemes it can be easily incorporated into the design of future quantum servers. These results will play a key role in enabling the development of secure distributed quantum systems.

Ultrafast time-bin qubits in PRL

We have a new paper Coherent Ultrafast Measurement of Time-Bin Encoded Photons by John Donohue, Megan Agnew, Jonathan Lavoie, and Kevin Resch which has just been published in Physical Review Letters.  The paper was chosen as an Editors Suggestion and reviewed in the article It’s a Good Time for Time-Bin Qubits by Todd Pittman (University of Maryland) in Physics.

Abstract: Time-bin encoding is a robust form of optical quantum information, especially for transmission in optical fibers. To readout the information, the separation of the time bins must be larger than the detector time resolution, typically on the order of nanoseconds for photon counters. In the present work, we demonstrate a technique using a nonlinear interaction between chirped entangled time-bin photons and shaped laser pulses to perform projective measurements on arbitrary time-bin states with picosecond-scale separations. We demonstrate a tomographically complete set of time-bin qubit projective measurements and show the fidelity of operations is sufficiently high to violate the Clauser-Horne-Shimony-Holt-Bell inequality by more than 6 standard deviations.

 

Squashing single photons in Nature Photonics

Our paper entitled, Spectral compression of single photons by Jonathan Lavoie, John Donohue, Logan Wright, Alessandro Fedrizzi (U. Queensland), and Kevin Resch, was published in Nature Photonics.

Abstract: Photons are critical to quantum technologies because they can be used for virtually all quantum information tasks, for example, in quantum metrology, as the information carrier in photonic quantum computation, as a mediator in hybrid systems, and to establish long-distance networks. The physical characteristics of photons in these applications differ drastically; spectral bandwidths span 12 orders of magnitude from 50 THz for quantum-optical coherence tomography to 50 Hz for certain quantum memories. Combining these technologies requires coherent interfaces that reversibly map centre frequencies and bandwidths of photons to avoid excessive loss. Here, we demonstrate bandwidth compression of single photons by a factor of 40 as well as tunability over a range 70 times that bandwidth via sum-frequency generation with chirped laser pulses. This constitutes a time-to-frequency interface for light capable of converting time-bin to colour entanglement, and enables ultrafast timing measurements. It is a step towards arbitrary waveform generation for single and entangled photons.

Congratulations

…to Jonathan for being chosen for an NSERC PDF and an IQC achievement award!

…to Deny for being selected for a 2013 UW Physics Special Graduate Scholarship and an IQC achievement award!

…to Kent for winning the Governor General Gold Medal for his outstanding MSc work!

…to Mike for successful completion of his MSc!

Update June 17, 2013 …to Kent for also winning the Dean of Science Award for his MSc work!
Update August 9, 2013 …to Jonathan for successfully defending his PhD!

Violation of new Bell's Inequalities in PRA

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.