Never try telling a quantum physicist that near enough is good enough – Australian researchers have invented a technique that, for the first time, measures lengths as accurately as the laws of physics allow.

In a paper published in leading international science journal Nature on 14 November 2007 the research team revealed a system that uses individual photons –particles of light – as a ruler for microscopic distances.

The apparatus used single photons, with each photon making a number of passes through the sample being measured.

Using just 36 photons making a total of 378 passes, the team was able to measure length differences less than one ten thousandth of the width of a human hair.

The experiment was performed in the laboratory of Dr Geoff Pryde at Griffith University's Centre for Quantum Dynamics, by him and his PhD student Brendon Higgins. Centre Director, Professor Howard Wiseman, developed the theory, together with University of Sydney's Dr Stephen Bartlett and Macquarie University's Dr Dominic Berry.

"This is an incredibly small amount of light." said Pryde.

"For comparison, scanning a barcode uses quadrillions of photons. Even the dim standby light on your DVD player shines out many trillions of photons a second."

"Similar schemes based on interferometry – a technique using waves of electromagnetic radiation such as light – have been used for centuries to measure length, and other properties of objects, with great accuracy." said Wiseman.

"The key difference is we have done it in a way that gets as much information out of each pass of a photon through the sample as is allowed by Heisenberg's uncertainty principle. In this sense, it’s the best measurement possible – something that’s never been done before."

"The obvious applications are in making accurate measurements using less light than was previously thought possible. This is particularly important in fields such as medical research, as passing light through a biological sample can damage it," said Pryde.

So why do we need to measure with such accuracy?

"Measurement underpins all science, and through history we've seen that advances in precision measurement lead to unexpected scientific discoveries, which in turn lead to new technologies and applications," Pryde said.

"Old-style interferometers taught us that the Earth wasn’t moving through a mysterious substance called 'aether', but actually through a vacuum. This ultimately led to Einstein’s theory of relativity. We don’t know yet where this new technique will lead us."

The team's next goal is to use more single photons and passes to get an even finer measurement.

"In principle this is possible, but there are some technological hurdles to overcome first!" said Pryde.