Research

Squeezed light is the workhorse of quantum light sources. By shining a strong laser on materials with nonlinear optical properties, photons from the laser field can scatter into pairs of lower-energy photons through processes called parametric down-conversion and four-wave mixing. These photon pair production processes yield "squeezed" beams of light that have reduced electrical field fluctuations. Due to energy and momentum conservation, the generated photon pairs also exhibit correlations in their spatial and frequency properties.

A significant portion of my research has been devoted to developing methods to characterize and measure these photon pairs. I am also interested in devising ways to enhance the strength of the scattering process to produce quantum-correlated beams of light beyond the pair generation regime.

Transition edge sensors (TESs) are superconducting photodetectors known for their exceptional energy resolution, enabling them to resolve the number of photons in an optical pulse with over 95% efficiency.  I have used these detectors to build a quantum-enhanced interferometer and a homodyne detector. 

Photon-number-resolving detectors, such as TESs or nanowires, are essential for efficiently preparing large-scale entangled states of light, which constitute the primary building blocks of a photonic quantum computer. Another promising application for these detectors is in quantum sensing. 

Currently, I am contributing to the commissioning of a TES system at the NRC. The accompanying photo captures me and my colleague installing fiber-optical cables in our adiabatic demagnetization refrigerator.

Light can exhibit a rich structure across its degrees of freedom, such as spatial shape, time-frequency shape, or polarization, especially when these are correlated. I am interested in developing techniques to fully and efficiently characterize the mode structure of light. Such techniques can be employed to extract information from light beams for sensing, communication, and information processing applications. Additionally, they are essential for verifying the purity of quantum light sources.

At the quantum level, there are several challenges for modal characterization. For instance, we cannot rely on self-induced nonlinearities, which are typically used in pulse characterization techniques like SPIDER and FROG. Moreover, quantum light sources can produce quantum-correlated photons, necessitating joint measurements to fully characterize their modal structure.

I have developed a technique based on intensity correlation interferometry between a quantum signal and a classical reference beam. With the help of colleagues, we have applied this technique to measure the joint spectral amplitude and phase of photon pairs produced by parametric down-conversion. We have also measured the spatial structure of single photons, such as the maple leaf shown in the image.

Multiparticle interference is the fundamental mechanism underlying the preparation of large entangled states—the cornerstone of quantum computers and quantum simulators. In the case of photons, this phenomenon can be explored through integrated photonic circuits. Quantum light is injected into networks of waveguides and directional couplers, as depicted in the image, where photons undergo interference. Consequently, the light at the chip's output becomes entangled in a complex manner.

Computational complexity primarily arises from performing measurements (e.g. photon counting) on subsets of this entangled state and conditionally updating the remaining state. I am intersted in the physics of multiparticle interference and identifying computational problems that can be addressed in the near term using small-scale photonic devices.