Professor recognized for scientific breakthrough

Physics World’s top 10 scientific breakthroughs of 2011 were revealed on December 16. U of T professor Aephraim Steinberg made it to the top of the list.

Steinberg and his colleagues at the Centre for Quantum Information and Quantum Control at U of T won the honour with their experimental work on the fundamentals of quantum mechanics using an emerging technique known as “weak measurement”.


A photon is a bundle, or “quantum”, of light energy. Photons are always in motion and move in distinct patterns. When a photon travels through two closely spaced slits, it creates an interference pattern on a screen behind, but if it has been determined which slit the photon will travel through, then the interference pattern disappears. This is why it was previously thought to be impossible to gain knowledge of a photon’s path.


This concept was originally debated by Niels Bohr and Albert Einstein in 1927.

Enter Steinberg and his team. They replaced the double slit with a beamsplitter and two optical fibres. When the photon hits the beamsplitter it travels along either the right or left fibre, allowing the path to be seen. It then exits at the end and creates an interference pattern on the screen. This makes it possible to watch the path of the photons and the interference pattern simultaneously.


The choice between first and second place was extremely difficult decision for Physics World, as the runner-up, a former colleague of Steinberg’s, was conducting a similar experiment.


Steinberg hopes that people will continue to ask science’s “forbidden questions” and discover further implications of quantum mechanics.

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