### Physics

# Upper limit found for quantum world

The red line shows the upper limit for parameters rc (margin on location) and λ (frequency of wave function collapse per atomic mass unit). The black dotted line gives the expectation for Oosterkamp’s next experiment. The purple ball estimates the values based on the fact that electrons definitely behave quantum mechanically around large molecules. In the end, the goal is to found the values for both parameters. This completes the formula for the boundary between the quantum and macroscopic world. For a given size and mass, this formula tells which laws apply to the object. Credit: Leiden Institute of Physics The quantum world and our world of perception obey different natural laws. Leiden physicists search for the border between both worlds. Now they suggest an upper limit in a study reported in Physical Review Letters. The laws of the quantum domain do not apply to our everyday lives. We are used to assigning an exact location and time to objects. But fundamental particles can only be described by probability distributions—imagine receiving a traffic ticket for speeding 30 to 250 km/h somewhere between Paris and Berlin, with a probability peak for 140 km/h in Frankfurt.

Boundary

Because the laws are completely different in both worlds, a clear boundary might exist between them. Size and mass could then be used to determine whether an object obeys quantum or macroscopic laws, but the edge of this boundary is elusive. Leiden physicist Tjerk Oosterkamp and his research group have now established established an upper limit for quantum phenomena, closing in on the answer.

’We keep excluding values, so that we slowly close in on the boundary’s location,’ says Oosterkamp. ’If we only have a small area left, we can better design our experiments to see what is happening at the edge of the quantum world.’

Parameters

According to a certain quantum mechanical model, you can describe a particle’s position with a probability distribution that sometimes spontaneously collapses. In that case, its position is, indeed, determined precisely, within a certain margin. This margin and how often the spontaneous collapse occurs are the two parameters that physicists seek. If they determine those, they have a complete formula to define a strict border between quantum and macro.

Oosterkamp has now determined an upper limit on these parameters of 31 collapses per year per atomic mass unit with a margin around 10 nanometers, to 1 collapse per 100 years with a margin of 1 micron. For their next measurement, the researchers expect fewer collapses, so they can define an even stricter upper limit.

Explore further:Physicists propose measure of macroscopicity; Schrodinger’s cat scores a 57

More information: Upper bounds on spontaneous wave-function collapse models using millikelvin-cooled nanocantilevers, A. Vinante, M. Bahrami, A. Bassi, O. Usenko, G. Wijts, and T.H. Oosterkamp, Physical Review Letters , 2016. arxiv.org/abs/1510.05791

Journal reference:Physical Review Letters

Provided by:Leiden Institute of Physics