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.

Non…Trajec in Science Advances local…tories

Our article, Experimental nonlocal and surreal Bohmian trajectories, by D. H. Mahler, L. Rozema, K. Fisher, L. Vermeyden, K.J. Resch, H.M. Wiseman, and A. Steinberg was published in Science Advances.  The work is the result of a collaboration between the University of Toronto, Griffith University, and University of Waterloo.

Abstract: Weak measurement allows one to empirically determine a set of average trajectories for an ensemble of quantum particles. However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle. Moreover, the theory describing these trajectories, called Bohmian mechanics, predicts trajectories that were at first deemed “surreal” when the second particle is used to probe the position of the first particle. We entangle two photons and determine a set of Bohmian trajectories for one of them using weak measurements and postselection. We show that the trajectories seem surreal only if one ignores their manifest nonlocality.

See also:
Realism is for people who can’t handle their nonlocality by A. Steinberg.
(Here is a link to the paper by Braverman and Simon referred to in the article as ‘further reading’)

Researchers demonstrate ‘quantum surrealism’ on

Quantum weirdness may hide an orderly reality after all on

Photon Icqubit published in PRL

Our article, Certifying the Presence of a Photonic Qubit by Splitting It in Two, by Evan Meyer-Scott, Daniel McCloskey, Klaudia Gołos, Jeff Z. Salvail, Kent A. G. Fisher, Deny R. Hamel, Adán Cabello, Kevin J. Resch, and Thomas Jennewein just appeared in Physical Review Letters.  The paper was chosen as an Editors’ Suggestion.

Abstract: We present an implementation of photonic qubit precertification that performs the delicate task of detecting the presence of a flying photon without destroying its qubit state, allowing loss-sensitive quantum cryptography and tests of nonlocality even over long distance. By splitting an incoming single photon in two via parametric down-conversion, we herald the photon’s arrival from an independent photon source while preserving its quantum information with up to (92.3±0.6)% fidelity. With reduced detector dark counts, precertification will be immediately useful in quantum communication.

Light Illuminated

Congratulations to Ian, Kent, Aimee, Sarah, Jean-Philippe, and Mike for their contribution to the exhibition ‘Light Illuminated: Celebrating Light & Light-based Technologies‘ at THEMUSEUM in Kitchener as part of the UN 2015 International Year of Light.  The exhibit effectively, interactively, and accessibly describes the physical aspects of light such as polarization, interference, and the speed of light; light-based technologies such as fibre optics, thermal imaging; and applications such as the laser maze (my kids’ favourite), an infinity mirror, 3D orientation recognition and optical ‘painting’.  The exhibition is on until March 28, 2016.




…to JP for being awarded the NSERC Vanier scholarship!

…to Mike for winning the NSERC CGS-D scholarship!

…to John for being recognized with an IQC achievement award and the David Johnston Award for Scientific Outreach!

…to Kent for winning the Ontario Graduate Scholarship!

…to Jeff for being awarded the NSERC CGS-D scholarship!

Quantum caus…………ality in Nature Physics

Our article, A quantum advantage for inferring causal structure, by Katja Reid, Megan Agnew, Lydia Vermeyden, Dominik Janzing, Rob Spekkens, and Kevin Resch just appeared in Nature Physics.  Giulio Chirabella wrote a News and Views piece on it entitled, Quantum information: Good causes.

Abstract: The problem of inferring causal relations from observed correlations is relevant to a wide variety of scientific disciplines. Yet given the correlations between just two classical variables, it is impossible to determine whether they arose from a causal influence of one on the other or a common cause influencing both. Only a randomized trial can settle the issue. Here we consider the problem of causal inference for quantum variables. We show that the analogue of a randomized trial, causal tomography, yields a complete solution. We also show that, in contrast to the classical case, one can sometimes infer the causal structure from observations alone. We implement a quantum-optical experiment wherein we control the causal relation between two optical modes, and two measurement schemes—with and without randomization—that extract this relation from the observed correlations. Our results show that entanglement and quantum coherence provide an advantage for causal inference.

Stories on IQC website here and Perimeter Institute website here.

Hi Efcncy Sngl Phtn Bndwth Cmprsn in PRA

Our article, Theory of high-efficiency sum-frequency generation for single-photon waveform conversion, by John Donohue, Mike Mazurek, and Kevin Resch was just published in Physical Review A.  The article studies the problem of single photon frequency conversion using sum-frequency generation, calculating how well the properties of the upconverted photon match a simpler first-order approximation.

Abstract: The optimal properties for single photons may vary drastically between different quantum technologies. Along with central frequency conversion, control over photonic temporal waveforms will be paramount to the effective coupling of different quantum systems and efficient distribution of quantum information. Through the application of pulse shaping and the nonlinear optical process of sum-frequency generation, we examine a framework for manipulation of single-photon waveforms. We use a nonperturbative treatment to determine the parameter regime in which both high-efficiency and high-fidelity conversion may be achieved for Gaussian waveforms and study the effect such conversion techniques have on energy-time entanglement. Additionally, we prove that aberrations due to time ordering are negligible when the phase matching is nonrestrictive over the input bandwidths. Our calculations show that ideal quantum optical waveform conversion and quantum time lensing may be fully realized using these techniques.

Quantum carats in PRL

Our new article Storage and Retrieval of THz-Bandwidth Single Photons Using a Room-Temperature Diamond Quantum Memory by D.G. England, K.A.G. Fisher, J-P.W. MacLean, P.J. Bustard,
R. Lausten, K.J. Resch, and B.J. Sussman was published in Physical Review Letters.  The work is the result of a great collaboration between our group and Ben Sussman’s Quantum Technology group at the National Research Council of Canada.  This work was selected for a synopsis in Physics and as an Editor’s suggestion.

Abstract: We report the storage and retrieval of single photons, via a quantum memory, in the optical phonons of a room-temperature bulk diamond. The THz-bandwidth heralded photons are generated by spontaneous parametric down-conversion and mapped to phonons via a Raman transition, stored for a variable delay, and released on demand. The second-order correlation of the memory output is g(2) = 0.65 ± 0.07, demonstrating a preservation of nonclassical photon statistics throughout storage and retrieval. The memory is low noise, high speed and broadly tunable; it therefore promises to be a versatile light-matter interface for local quantum processing applications.

Update March 8, 2015: Our work was covered in an article by S.M. Dambrot on

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.


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,, and the Popular Science website


…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!