Indian researchers have experimentally measured a quantum measure of 1.17, exceeding the upper limit of one that applies to ordinary probability. The experiment was conducted by physicists at the Raman Research Institute (RRI) and reported on September 24.
The result relates to Quantum Measure Theory (QMT), a framework that describes quantum systems through possible histories rather than only their states and measurement outcomes. In this approach, a quantum measure can account for interference between different possible paths taken by a particle or photon.
The RRI team developed an “event-filter” to select a particular collection of photon paths in an optical setup. The researchers used polarisation to distinguish different routes and later erased that information so the paths could interfere.
Sanchari Chakraborti, then a PhD student at RRI, conducted the experiment under the supervision of senior professor Urbasi Sinha. The team measured laser power at the input and output before using the calibrated event-filter to determine the quantum measure.
The measured value of about 1.17 was close to the theoretical prediction of 1. after accounting for imperfections in the experimental setup. The researchers stressed that this does not mean a probability greater than one was measured. The ordinary photon-detection probability remained below one.
The experiment demonstrates that a quantum measure exceeding one, previously treated as an abstract mathematical quantity, can be measured in a laboratory. The researchers said the event-filtering approach could potentially become a tool for quantum measurement and quantum computing. The study was published in the journal Quantum.
