Going beyond the usually known use of quantum computers --- performing certain tasks at an exponentially faster rate than classical computers, scientists have for the first time used quantum computers for a novel purpose. They have used the new age computers to directly test the very foundations of the theory on which their working is based.

Quantum mechanics like any physical theory is based on experiments. This means that experiments are used to justify some axioms from which the full theory can be logically deduced. While a large section of the scientific community is invested in building devices towards quantum computing applications, a separate community is invested in precision tests of fundamental aspects of quantum theory itself.

A group of scientists from the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology in a collaborative research have used quantum computers to perform some precision tests of the fundamental aspects of the quantum theory called Sorkin and Peres tests. The first is a test of the probabilistic aspect of quantum mechanics which helps calculate the chances of events happening while the second is a test of an aspect of the superposition principle, which expresses the fact that quantum objects may behave as waves -- throwing two stones in a pond gives a wave pattern which is the sum of two waves.

The collaborative work started through a discussion between Professor Urbasi Sinha of RRI Bangalore and conference delegate Prof. Lorenzo Macconne from University of Pavia, Italy during the Quantum Frontiers and Fundamentals (QFF 2020) conference hosted by RRI Bangalore in January 2020. Over the next two years Prof. Sinha, with long standing expertise and contributions in the domain of precision tests of quantum mechanics, along with her post doc explored the possibility of performing experiments on quantum computers with Prof. Macconne, an expert on quantum information theory. 

The use of a quantum computer to perform tests of crucial quantum principles in the research published as rapid communication letter in the journal Physical Review Research has led to the natural emergence of an entirely new research direction for the physics community that brings together diverse research disciplines under one unifying umbrella.

As quantum computers are scalable quantum systems, this could provide a universal programmable setup for quantum experiments. A quantum circuit, which is like a low-level program for quantum computers, could be a Rosetta stone that allows translation of experiments from one physical system to another.

As a corollary, the scientists have also shown that quantum mechanics is true and the tests can be used as a benchmark to evaluate how well a quantum computer performs. “Our method provides a nice way to create well defined benchmarks for quantum computers so that we know exactly how error prone they are, by using the very foundations of quantum theory as the benchmarking tool,” said Professor Sinha.

Publication:

DOI: 10.1103/PhysRevResearch.4.L022001

Testing quantum foundations with quantum computers, S. Sadana, L. Macconne, U.Sinha, Physical Review Research, 4 L022001, 2002.