Research Breakthrough: uOttawa Physicist Makes First Direct Measurements Of Quantum States Of Light

A groundbreaking discovery by a team led by Robert Boyd, Canada Excellence Research Chair in Quantum Nonlinear Optics at the University of Ottawa and professor of optics and physics at the University of Rochester, has enabled the first direct measure of polarization states of photon light, the directions in which the electric and magnetic fields of light oscillate. The research also questions the key tenet of Heisenberg’s uncertainty principle.

The findings, published this week in Nature Photonics, show for the first time that it is possible to directly measure key related variables (known as “conjugate” variables) of a quantum particle or state. This new insight challenges the uncertainty principle, which postulates that when measuring certain properties of a quantum system with precision, other related properties will not be measured with the same accuracy.

The researchers’ direct measurement technique employs a “trick” to measure the first property in such a way that the system is not disturbed and information about the second property can still be obtained.This careful process relies on a “weak measurement” of the first property followed by a “strong measurement” of the second property.

“The ability to perform direct measurement of the quantum wave function has important implications for quantum information science,” explained Boyd, “Ongoing work in our group involves applying this technique to other systems, for example, measuring the form of a ‘mixed’ (as opposed to a pure) quantum state.”

Until recently, quantum states of light could only be measured using indirect procedures, such as quantum tomography, a time-consuming process requiring intensive post-processing of data. Using direct measurement, researchers are able to pull the same information as quantum tomography but in significantly less time.

The research team also included associate researcher Jonathan Leach, University of Ottawa undergraduate students Jeff Z. Salvail, Megan Agnew and Allan S. Johnson, and graduate student Eliot Bolduc.

About the Canada Excellence Research Chairs
Launched in 2008, the Canada Excellence Research Chair program was created to attract the world’s most accomplished and promising minds to develop ambitious research programs in priority areas of the Government of Canada's science and technology (S&T) strategy.

About the University of Ottawa
The University of Ottawa is committed to research excellence and encourages an interdisciplinary approach to knowledge creation, which attracts the best academic talent from across Canada and around the world. The University plays an important role in the economic development of the National Capital Region.