Our paper, Phonon-Mediated Nonclassical Interference in Diamond, by Duncan England, Kent Fisher, Jean-Philippe MacLean, Philip Bustard, Khabat Heshami, Kevin Resch, and Benjamin Sussman was published in Physical Review Letters. This work is the result of a collaboration with Ben Sussman’s Quantum Technologies Laboratory at the National Research Council Canada.
Abstract: Quantum interference of single photons is a fundamental aspect of many photonic quantum processing and communication protocols. Interference requires that the multiple pathways through an interferometer be temporally indistinguishable to within the coherence time of the photon. In this Letter, we use a diamond quantum memory to demonstrate interference between quantum pathways, initially temporally separated by many multiples of the optical coherence time. The quantum memory can be viewed as a light-matter beam splitter, mapping a THz-bandwidth single photon to a variable superposition of the output optical mode and stored phononic mode. Because the memory acts both as a beam splitter and as a buffer, the relevant coherence time for interference is not that of the photon, but rather that of the memory. We use this mechanism to demonstrate nonclassical single-photon and two-photon interference between quantum pathways initially separated by several picoseconds, even though the duration of the photons themselves is just ∼250 fs.
Our article, An experimental test of noncontextuality without unphysical idealizations, by Mike Mazurek, Matt Pusey, Ravi Kunjwal, Kevin Resch, and Rob Spekkens was just published in Nature Communications. This work is the result of a collaboration between IQC and the Perimeter Institute on Experimental Quantum Foundations.
Abstract: To make precise the sense in which nature fails to respect classical physics, one requires a formal notion of classicality. Ideally, such a notion should be defined operationally, so that it can be subject to direct experimental test, and it should be applicable in a wide variety of experimental scenarios so that it can cover the breadth of phenomena thought to defy classical understanding. Bell’s notion of local causality fulfils the first criterion but not the second. The notion of noncontextuality fulfils the second criterion, but it is a long-standing question whether it can be made to fulfil the first. Previous attempts to test noncontextuality have all assumed idealizations that real experiments cannot achieve, namely noiseless measurements and exact operational equivalences. Here we show how to devise tests that are free of these idealizations. We perform a photonic implementation of one such test, ruling out noncontextual models with high confidence.
Patrick Daley has joined us for the summer from McMaster University to work in the group and attend the USEQIP summer school. Welcome Patrick!
Our new article Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory by K.A.G. Fisher, D.G. England, J.-P.W. MacLean, P.J. Bustard, K.J. Resch, and B.J. Sussman was published in Nature Communications. The work is the result of our collaboration with Ben Sussman’s Quantum Technology group at the National Research Council of Canada.
Abstract: The spectral manipulation of photons is essential for linking components in a quantum network. Large frequency shifts are needed for conversion between optical and telecommunication frequencies, while smaller shifts are useful for frequency-multiplexing quantum systems, in the same way that wavelength division multiplexing is used in classical communications. Here we demonstrate frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory. Heralded 723.5 nm photons, with 4.1 nm bandwidth, are stored as optical phonons in the diamond via a Raman transition. Upon retrieval from the diamond memory, the spectral shape of the photons is determined by a tunable read pulse through the reverse Raman transition. We report central frequency tunability over 4.2 times the input bandwidth, and bandwidth modulation between 0.5 and 1.9 times the input bandwidth. Our results demonstrate the potential for diamond, and Raman memories in general, as an integrated platform for photon storage and spectral conversion.
See also a write-up on our work:
Changing the colour of single photons in a diamond quantum memory, phys.org
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.
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 Phys.org.
Quantum weirdness may hide an orderly reality after all on NewScientist.com
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.
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!
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.
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.