For the first time, scientists have managed to show quantum entanglement – which Einstein famously described as "spooky action at a distance" – happening between macroscopic objects, a major step forward in our understanding of quantum physics.
Quantum entanglement links particles in a way that they instantly affect each other, even over vast distances. On the surface, this powerful bond defies classical physics and, generally, our understanding of reality, which is why Einstein found it so spooky. But the phenomenon has since become a cornerstone of modern technology.
Still, up until now quantum entanglement has only been demonstrated to work at the smallest of scales, in systems based on light and atoms, for example.
Any attempt to increase the sizes has caused problems with stability, with the slightest of environmental disturbances breaking the connection.
But new research changes all of this, by demonstrating that this 'spooky action' can indeed be a reality between massive objects.
We're not talking massive in the black hole sense but in the macroscopic sense – two 15-micrometre-wide vibrating drum heads.
And the next step will be to test whether those vibrations are being teleported between the two objects.
"Our work qualitatively extends the range of entangled physical systems and has implications for quantum information processing, precision measurements, and tests of the limits of quantum mechanics," write the researchers.
Building on research stretching back to 2014, the new experiments used two vibrating drumheads to represent massive objects, or massive mechanical oscillators to use the technical term.
Each one was 15-micrometres in diameter, about the width of a human hair. Not massive to us, but massive compared to the atomic scales previously used to demonstrate quantum entanglement – each drumhead was composed of trillions of atoms.
To achieve their results, the team cooled a superconducting electrical circuit to just above absolute zero, about -273 degrees Celsius (-459.4 degrees Fahrenheit). This was then controlled and measured using weak microwave fields.
Through the application of microwaves, the drumheads on the circuit were able to vibrate at a high ultrasound frequency, producing the vibrations that formed the peculiar quantum state that had Einstein scratching his head about in the 1930s.
"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," says one of the team, Matt Woolley from the University of New South Wales in Australia.
The extremely low temperatures and the circuit's electrical fields removed all forms of disturbance and interference from the drumheads, leaving only the quantum mechanical vibrations behind.
Another impressive feat was keeping the entangled state for almost half an hour – previous experiments have struggled to reach fractions of a second.
Now that this breakthrough has been made at a scale approaching what we can see with the naked eye, it has the potential to lead to all kinds of new discoveries in the field: from how gravity and quantum mechanics work together, to the possibility of teleporting mechanical vibrations across entangled objects.
"The next step is to demonstrate teleportation of the mechanical vibrations," says Woolley. "In teleportation, the physical properties of an object can be transmitted using the channel of `spooky action'."
Einstein himself described it as like two halves of the same coin, split up: if you have heads, the other half must be tails, even if it's millions of light-years away.
"In quantum teleportation, properties of physical bodies can be transmitted across arbitrary distances using the channel of 'spooky action at a distance'," says one of the team, Caspar Ockeloen-Korppi from Aalto University in Finland.
"We are still pretty far from Star Trek, though."
While it's hard to say where this work will lead us next, it can't be understated how important it is that we've taken this first step into macroscopic quantum mechanics.
"It is clear that the era of massive quantum machines has arrived," Woolley explains in a piece for The Conversation. "And is here to stay."
The research has been published in Nature.