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June 28, 2011— Ottawa, Ontario

Researchers around the world now have a new method of investigating the smallest particles of nature, which are governed by the laws of quantum mechanics. In a recent study published in the journal Nature, NRC scientists reported a way to directly measure a photon’s “wavefunction” — and thereby know everything there is to know about this quantum mechanical system. 

Invented early last century, quantum mechanics describes the microscopic world of very simple systems involving a small number of basic particles, such as photons, atoms or electrons. Quantum mechanics allows scientists to study phenomena that cannot be adequately described using Newtonian mechanics, a theory which explains the everyday world — like how a baseball flies or why the Earth circles the Sun.

Artistic impression of a photon’s wavefunction at the moment that it is being measured.

Artistic impression of a photon’s wavefunction at the moment that it is being measured.

The wavefunction lies at the heart of quantum mechanics. “Every object in the universe has a quantum wavefunction that determines and predicts how it will act and also react to other objects,” says Dr. Jeff Lundeen of the NRC Institute for National Measurement Standards in Ottawa. Knowing an object’s wavefunction, one can calculate where a particle is most likely to be or how fast it’s likely to be moving. Such information can be applied to everything from quantum computing and metrology to drug design and microelectronics.

“The wavefunction embodies the idea that every particle is also a wave,” adds Dr. Lundeen, who co-led the NRC research team along with Dr. Charles Bamber. “This wave is much like the set of ripples travelling out from a pebble dropped in a pool. A unique feature of the wavefunction is that, unlike a water wave, the very act of observing it changes it, making it a slippery object to measure.”

Heisenberg’s Uncertainty Principle 

Due to Heisenberg’s Uncertainty Principle, which states that the more precisely one can measure the current position of a particle, the less precisely one can measure its momentum, scientists have long viewed the wavefunction as a purely abstract mathematical tool. 

However, using a technique called “weak measurement,” the NRC team found it’s possible to learn something about a photon’s wavefunction without altering it. “The catch is that you get very little information about a single photon. But if you perform the measurement over and over on identical photons, you can eventually find the average wavefunction,” explains Dr. Lundeen.

Quantum computing and the wavefunction

First envisaged about 50 years ago, quantum computers are being designed to operate differently than current computers by harnessing a single photon or atom to carry information. “In quantum computing, the wavefunction would play a very explicit role in that we would manipulate and use it to process the information,” says Dr. Jeff Lundeen of NRC.

“In a quantum computer, you would use quantum mechanics to solve computational problems that you can’t solve using a normal computer,” he adds. “One example may involve modelling the behaviour of small molecules such as drugs, which are collections of atoms — each with its own wavefunction.” How all those wave functions interact determines how the drug works.

According to Dr. Bamber, the NRC team’s method could be applied to any microscopic particle. “We have shown that it works for determining the wavefunction of a photon, so there is no reason to believe it won’t work for other particles too.”

The development of this direct measuring method could ultimately allow scientists to design better drugs and chemicals, and build faster computer processors in the decades to come. The NRC discovery keeps Canada at the forefront of the development of quantum computers. Quantum computers would be able to solve problems that no regular computer ever could, including breaking encryption codes.

Related information

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National Research Council of Canada

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