Calgary, Alberta, Canada. Peering into ever smaller spaces, and doing so with high degrees of accuracy and precision, is increasingly important to fields as diverse as molecular biology and metallurgy.

However, quantum physics works fantastically well on small scales but not when it comes to larger scales; it is nearly impossible to count photons very well.


Researchers from the universities of Calgary and Waterloo in Canada, and the University of Geneva in Switzerland, have published a paper in the Physical Review Letters explaining why we don't usually see the physical effects of quantum mechanics. "We have demonstrated that this makes it hard to see these effects in our daily life," says Dr. Christoph Simon, a lead author who teaches in the Department of Physics and Astronomy at the University of Calgary.



Christoph Simon, PhD, is an associate professor who teaches physics at the University of Calgary.

Photo courtesy of the Faculty of Science.It is well known that quantum systems are fragile. When a photon interacts with its environment, even just a tiny bit, the superposition is destroyed, a fundamental principle of quantum physics that says that systems can exist in all their possible states simultaneously. But when measured, only the result of one of the states is can be observed.

This effect is known as decoherence, and it has been subjected to intense study intensively over the last few decades. The idea of decoherence as a thought experiment was raised by Erwin Schrödinger, one of the founding fathers of quantum physics, in his famous cat paradox: a cat in a box can be both dead and alive at the same time.

But, according to the authors of this study, it turns out that decoherence is not the only reason why quantum effects are hard to see. Seeing quantum effects requires extremely precise measurements. Simon and his team studied a concrete example for such a "cat" by using a particular quantum state involving a large number of photons.

"We show that in order to see the quantum nature of this state, one has to be able to count the number of photons in it perfectly," says Simon. "This becomes more and more difficult as the total number of photons is increased."

Are there parallel universes? And how will we know? Simon says that "Distinguishing one photon from two photons is within reach of current technology, but distinguishing a million photons from a million plus one is not."

This is one of many fascinations people hold about quantum physics.

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