A single photon detector. Credit: Max4e Photo / Alamy Stock Photo
Physicists have devised a loophole-free experiment using single photons which disproves the classical notion that the properties of all objects always have definite values, independent of experimental measurement1.
The behaviour of single photons observed in the experiment is fundamentally incompatible with the laws of classical physics that large objects obey.
The inherent non-classicality of single photons can be reliably and efficiently harnessed for various applications such as secure information transfer, says a team at the Raman Research Institute (RRI) in Bangalore.
The scientists, led by Urbasi Sinha at RRI with theoretical inputs from Dipankar Home at the Bose Institute in Kolkata, performed the experiment by shining a laser beam on a beta barium borate crystal, making it emit pairs of single photons. A filter placed next to the crystal blocked the laser beam, letting only the single-photon pairs pass through.
One photon from a pair of single photons reached a detector. The other, after being reflected off a mirror, made its way to two interferometers. In the interferometers, single photons were divided into two paths that were recombined to produce an intensity pattern on another detector.
This led to photon detection which, coupled with correlation measurements, identified specific delicate signals that proved the quantumness of single photons. This experiment plugged the loopholes of previous experiments, including reducing noise caused by multiphoton emissions.
The results also violated Leggett-Garg Inequality (LGI), a mathematical theory which was originally proposed to test whether the laws of quantum physics prevail in the realm of large objects, the researchers say.
