We stride through our Universe with the confidence of a giant, giving little thought to the fact that reality bubbles with uncertainty.
But physicists have just served up a sharp reminder that even our macroscopic world is subject to the laws of quantum physics – by successfully entangling a millimetre-sized drum with a large cloud of atoms.
The researchers from the Niels Bohr Institute at the University of Copenhagen conducted the experiment using a 13 nanometre-thick, millimetres-long silicon nitride membrane (or drum) that buzzed lightly when struck with photons.
Those photons, or particles of light, came courtesy of a thin fog of a billion caesium atoms spinning inside the confines of a small, cold cell.
Despite being two very different objects, the millimetres-long drum and the fog of atoms represent an entangled system – and they push the limits of quantum mechanics.
“The bigger the objects, the further apart they are, the more disparate they are, the more interesting entanglement becomes from both fundamental and applied perspectives,” says senior researcher Eugene Polzik.
“With the new result, entanglement between very different objects has become possible”.
Entanglement is one of those concepts that feels far more mystical than intuitive, describing a connection between objects that exists independently of time and space.
No matter how far apart, or how many years have passed, a change to one part of an entangled system prompts an immediate adjustment to the rest.
More than once, Einstein referred to the concept as a ‘spooky action at a distance’, believing it had more to do with a shortfall in our knowledge than anything truly bizarre.
A century on, our understanding of quantum physics not only leaves plenty of room for such spookiness, it is forming the basis of amazing new fields of innovation, from super strong encryption to new kinds of radar.
“Quantum mechanics is like a double-edged sword,” says quantum physicist Michał Parniak from the Niels Bohr Institute.
“It gives us wonderful new technologies, but also limits precision of measurements which would seem just easy from a classical point of view.”
In isolation, a single particle’s properties are an anxious mess of possibility represented by the rise and fall of a wave. It moves in all directions at once. Spins in two directions at the same time. It’s all and it’s nothing.
As the particle interacts with other objects, its uncertainty doesn’t immediately vanish, but combines in complex ways we can model mathematically.
It’s these very predictable computations that make up the backbone of quantum computers. Yet such tech relies on the spin of a small number of relatively identical particles.
That’s why this latest breakthrough is so important – a visible drum wobbling in a breeze of photons wafting from a cloud of atoms is a whole other ballgame for physicists.
Being able to observe entanglement on a larger scale, one that involves a diversity of materials, is like studying a language that could be applied to quantum conversations.
This would be incredibly useful for ‘listening’ in on tools that require incredibly fine precision. Knowing how their quantum probabilities combine is a critical step in knowing how to sift out meaning in what otherwise seems like chaos.
Take the enormous array or lasers making up the Laser Interferometer Gravitational-wave Observatory (LIGO), for example. Though immense, the heart of the device lines up light waves with such precision that the very hum of uncertainty in an empty vacuum risks making a mess of it.
Entangling macroscopic systems like LIGO’s mirrors could – in theory – allow researchers to better account for a degree of quantum uncertainty.
A millimetre wide drum is admittedly a tiny step by comparison. But for giants like us, it’s a crucial opportunity for listening carefully to the way reality shakes beneath our feet.
This research was published in Nature.