More proof of Einstein’s ‘spooky action at a distance’ keeps popping up

The elusive quantum mechanical phenomenon of entanglement has now been made a reality in massive objects.

Results published in Nature show that two vibrating drumheads, each the width of a human hair, can display the “spooky action at a distance” that famously troubled Einstein.

The discovery was made by an international team of researchers including UNSW Canberra Senior Lecturer Matt Woolley.

“This demonstration is the culmination of several years’ work,” Dr Woolley says.

Such work opens the door to the future demonstration of teleportation between massive objects and the study of the poorly understood interplay between quantum mechanics and gravity.

Entanglement, whereby two distant objects become intertwined in a manner that defies both classical physics and a “common sense” understanding of reality, is perhaps one of the strangest phenomena of quantum theory. In 1935, Einstein expressed his concern over this concept, referring to it as a “spooky action at a distance”.

Nonetheless, entanglement is now considered a cornerstone of quantum mechanics, and is the key resource behind a host of potentially transformative quantum communication and computation technologies. It is, however, extremely fragile, and has previously only been observed with microscopic systems such as light or atoms, and more recently, with electrical circuits.

In 2014, Dr Woolley, in collaboration with Professor Aashish Clerk (now at the University of Chicago), showed theoretically that entanglement of the motion of massive objects could be prepared and detected in a superconducting electrical circuit incorporating two vibrating drumheads as the massive objects.

Dr Woolley then collaborated with Professor Mika Sillanpää and his team at Aalto University in Finland to realise this vision.

The team has prepared and detected quantum entanglement of the motion of massive objects, each with a diameter about the width of a human hair and each composed of trillions of atoms.

The experiment has been realised by precisely fabricating a superconducting electrical circuit, cooling it to about -273°C (just above absolute zero), and then carefully controlling and measuring it using weak microwave fields.

“It is, of course, immensely satisfying to see the vision that you have laid out come to fruition, and exciting to imagine where experiments like this might ultimately lead, and what fundamental insights and technological development they might ultimately yield,” Dr Woolley says.

“The next step is to demonstrate teleportation of the mechanical vibrations. In teleportation, the physical properties of an object can be transmitted using the channel of `spooky action’.”

The measurements demonstrate that control over massive mechanical objects is now at the level where exotic quantum states can be generated and stabilised.

This opens the door to new kinds of quantum sensing, communication and computation technologies, but could also enable studies of fundamental physics, such as the poorly understood interplay of gravity and quantum mechanics.

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