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

Jun 02, 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: Optimum inertial self-propulsion design for snowman-like nanorobot

add to favorites email to friend print save as pdf

Related Stories

Quantum leap in lasers brightens future for quantum computing

Jul 22, 2014

Dartmouth scientists and their colleagues have devised a breakthrough laser that uses a single artificial atom to generate and emit particles of light. The laser may play a crucial role in the development of quantum computers, ...

Quantum tech disappoints, but only because we don't get it

Jul 16, 2014

Over the next five years, the UK government will spend £270m on supporting research in "quantum technology". When budget announcements were made in 2013, provisions for offshore wind and shale gas extraction were received ...

Surrey NanoSystems has "super black" material

Jul 15, 2014

(Phys.org) —A British company says it has scored a breakthrough in the world's darkest material. Surrey NanoSystems describes its development as not just a black material but super-black. They are calling ...

Recommended for you

Verifying the future of quantum computing

9 minutes ago

Physicists are one step closer to proving the reliability of a quantum computer – a machine which promises to revolutionise the way we trade over the internet and provide new tools to perform powerful simulations.

A transistor-like amplifier for single photons

Jul 29, 2014

Data transmission over long distances usually utilizes optical techniques via glass fibres – this ensures high speed transmission combined with low power dissipation of the signal. For quite some years ...

User comments : 0