Experiments test Penrose’s hypothesis on massive quantum superpositions

The quantum superposition of a massive object represents a thought experiment that pits the theories of general relativity and quantum mechanics against one other. The issue comes about when time dilation is considered, which leads to no unique definition of time in quantum mechanics. Sir Roger Penrose proposed a theory that superpositions experience a collapse of their wavefunctions due to general relativity.

Gely and Steele report on the possibility of using mechanical oscillators to experimentally study such massive quantum superpositions. They outline the various conditions that oscillators should obey to test hypotheses like Penrose’s and advance the understanding of how quantum mechanics and general relativity can be combined.

“There’s a field of research called optomechanics, which is trying to manipulate heavy objects in a quantum mechanical way,” said author Mario Gely. “In this field, a lot of people are nowadays motivated by technological applications, such as interconnecting quantum computers. But using this experimental platform to test Penrose’s idea could touch on something very deep -- the interplay between quantum mechanics and general relativity.”

The researchers explore different types of clamped mechanical oscillators coupled to superconducting circuits: acoustic oscillators, beams, and membranes or drums. They performed relevant calculations, such as how heavy the object should be and how long a superposition should be sustained, to evaluate the suitability of each oscillator for measuring the effects of general relativity in massive superpositions.

They concluded low-frequency silicon nitride membranes manipulated into small cat-states, or Fock-states, or low-frequency acoustical resonators manipulated into quantum states with over a million phonons would be most appropriate for experiments.

Source: “Superconducting electro-mechanics to test Diósi-Penrose effects of general relativity in massive superpositions,” by Mario Florentin Gely, and Gary Alexander Steele, AVS Quantum Science (2021). The article can be accessed at http://doi.org/10.1116/5.0050988 .

This is part of a special collection Celebrating Sir Roger Penrose’s Nobel Prize. More papers can be found here: https://avs.scitation.org/toc/aqs/RPNP2021/1 .