Ottawa physicist measures 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

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

“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.

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