New physics law sheds light on measurement precision

29 October 2010

New physics law sheds light on measurement precision

Researchers from the University of Sheffield have discovered a new law of physics that determines exactly what it costs to make a measurement with a certain precision.

The discovery by Dr Pieter Kok and his team from the University´s Department of Physics and Astronomy, which was published today (29 October 2010) in the journal Physical Review Letters, will hopefully help with the detection of elusive gravitational waves, and open up new levels of miniaturisation in nanotechnology.

Precision measurements are the engine of scientific and technological progress. Applications include gravitational wave detection, in which the space-bending waves generated by colliding black holes can finally be registered here on Earth. These waves are predicted in Einstein´s theory of general relativity, but they have so far eluded direct observation.

Another application is in the continuing miniaturisation of technology: smaller devices require ever more precise engineering, and at the same time become increasingly fragile. To have a sufficiently good level of control with only few resources, such as photons (elementary particles), which in large numbers could destroy the device, it may be necessary to make use of a mysterious property called `quantum entanglement.´

Since the 1990s, the so-called `Heisenberg limit´ was thought to set the greatest achievable precision in any possible measurement. The limit says that the maximum precision using entangled photons is much better than the precision achievable with ordinary light. Recently, however, it was shown that this limit could be surpassed in certain `nonlinear´ optical procedures, and it was therefore invalidated.

Now, Dr Kok and his team have formulated the ultimate `Heisenberg limit´ that applies to all conceivable measurement procedures. One of the key insights that led to this new result was the correct identification of the cost of achieving higher precision. This was calculated using computational complexity theory, which is a branch of computer science that studies how `hard´ various computational problems are. This further strengthens the connection between physics and computer science.

Like other fundamental limits, the new `Heisenberg limit´ increases our understanding of nature, and will most likely lead to new recipes for high-precision measurements.

Dr Pieter Kok, from the University of Sheffield´s Department of Physics and Astronomy, said: "This is a very exciting result. For years, we have been puzzled about the precise meaning of this `Heisenberg limit,´ and now we have a full understanding of the cost involved if we want to make a measurement twice as precise."