Observing a Photon no Longer a Seek-and-Destroy Mission

June 2, 2004

A team of University of Queensland, Australia physicists has devised a sophisticated measurement system for single particles of light, or photons, enabling them to investigate fascinating behaviour in the quantum world.

In a world-first, the path of a single photon can now be measured without destroying the photon in the process.

One of the most surprising and unexpected aspects of quantum mechanics is the propensity for a photon to behave both like a particle and a wave.

The measurement developed at the Centre for Quantum Computer Technology within UQ’s School of Physical Sciences has enabled these wave-like and particle-like properties of a single photon to be observed simultaneously.

The breakthrough innovation by Drs Geoff Pryde, Jeremy O’Brien, Andrew White, Stephen Bartlett and Associate Professor Tim Ralph was recently published in the American Physical Society’s Physical Review Letters.

The quintessential experiment demonstrating the wave-like properties of light was English physicist Thomas Young’s c.1801 experiment where light was shone on a pair of holes in a screen. Interference between the two possible paths gave rise to an interference pattern on a second screen behind the holes — a wave-like phenomenon.

The remarkable thing is that this wave-like behaviour persists even when the light is so dim that only a single photon is present in the apparatus at any given time.

“That is unless the experimenter observes a particle-like property by measuring which path the photon took — in that case the interference disappears,” Dr O’Brien said.

In the UQ experiment, the researchers found that indeed the more particle-like the photon’s behaviour was, the less wave-like behaviour was observed, and vice versa.

The experiment shows once and for all that light is essentially fickle — sometimes behaving as particles and at others, like waves.

To measure the path of single photon, the team observed a second photon which carried away information about the first after the two interacted.

The experiment involved shining a powerful ultra-violet laser in to a special crystal to produce the two photons; a circuit of optical fibres; lenses and other optical elements; and normal destructive single photon detectors.

The original news release can be found on the University of Queensland web-site.

Explore further: Light and matter merge in quantum coupling

Related Stories

Light and matter merge in quantum coupling

August 22, 2016

Where light and matter intersect, the world illuminates. Where light and matter interact so strongly that they become one, they illuminate a world of new physics, according to Rice University scientists.

'Sniffer plasmons' could detect explosives

August 16, 2016

Physicists from the Moscow Institute of Physics and Technology (MIPT) have found that graphene might be the ideal material for manufacturing plasmonic devices capable of detecting explosive materials, toxic chemicals, and ...

UA engineers twist physics laws to boost sonic science

August 17, 2016

For decades, advances in electronics and optics have driven progress in information technology, energy and biomedicine. Now researchers at the University of Arizona are pioneering a new field—phononics, the science of sound—with ...

Recommended for you

Rocky planet found orbiting habitable zone of nearest star

August 24, 2016

An international team of astronomers including Carnegie's Paul Butler has found clear evidence of a planet orbiting Proxima Centauri, the closest star to our Solar System. The new world, designated Proxima b, orbits its cool ...

Feeling the force between sand grains

August 24, 2016

For the first time, Lawrence Livermore National Laboratory (LLNL) researchers have measured how forces move through 3D granular materials, determining how this important class of materials might pack and behave in processes ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.