Quantum nature of large objects

“Is the Moon there when no one is looking at it?”— Albert Einstein’s famous comment aptly describes the bizarreness of quantum mechanics, which, despite being a fundamental branch of physics providing insights into the development of computers and smartphones, is yet to be tested in a laboratory on an object bigger than atoms or molecules.

An Indo-UK group of researchers have now proposed an experiment to test the quantumness of an object regardless of its mass. Funded by the UK Engineering and Physical Sciences Research Council, the experiment is already underway.

The team comprising Dipankar Home from Bose Institute, Kolkata; Sougato Bose and Debarshi Das from University College London; and Hendrik Ulbricht at the University of Southampton can provide answers to queries like whether quantum mechanics is valid from the micro world to all the way to the everyday world for massive objects. It can also confirm the possibility of a Schrödinger Cat-like situation for large bodies.

Nearly a century ago, Erwin Schrödinger, one of the forefathers of quantum mechanics, proposed history’s most famous thought experiment to provide an example of the weird nature of the quantum world. He argued that the laws of quantum mechanics would allow a cat under certain conditions to be neither dead nor alive until it is observed. Physicists call this a superposition of two states.

So far, the demonstration of quantumness, like the Schrödinger Cat-like behaviour, has been shown only up to large molecules of masses ten thousand times the hydrogen atom. But for testing the quantumness of gravity—considered a Holy Grail in physics—the systems involved must be massive, at least a trillion times the hydrogen atom, for which the quantumness must first be demonstrated.

Most physicists believe quantum mechanics holds true at larger scales, but is extremely hard to observe due to the isolation required to preserve a quantum state.

“Our proposed experiment can test if an object is classical or quantum by seeing if an act of observation can lead to a change in its motion,” said Das. “The experiment has just been initiated at the University of Southampton and is expected to take a couple of years. It will provide the most emphatic demonstration of macro-quantumness to date apart from having the potentiality for applications like very accurate quantum sensing,” Home told DH.

The outline of the experiment was published in the Physical Review Letters.