Quantum physicists have set a new record for collecting a persistent group of entangled atoms together, getting 15 trillion atoms to co-exist in a "hot and messy" cloud of gas.
Quantum entanglement is the phenomenon at the heart of quantum physics, where two particles can mysteriously influence each other, no matter what the distance is between them – so measuring one of them instantly gives us the measurement of the other.
While scientists don't yet fully understand why this occurs, it does indeed happen; but demonstrating quantum entanglement remains a delicate and challenging process.
Entangled states need some very specific conditions to exist and survive, with most experiments in this area of research being conducted at temperatures approaching absolute zero.
Artistic illustration of the atom cloud. (ICFO)
That's why this new study is such an achievement. The scientists were able to create a hot, chaotic gas of atoms heated to about 450 Kelvin (177° C or 350° F), packed full with around 15 trillion entangled atoms – around 100 times more than have ever been observed together before.
These atoms weren't isolated either: measurements taken by lasers showed them colliding into each other, and there were sometimes thousands of other atoms between entangled pairs. The experiment also showed the state of entanglement may be stronger than previously realised.
"If we stop the measurement, the entanglement remains for about 1 millisecond, which means that 1,000 times per second a new batch of 15 trillion atoms is being entangled," says quantum physicist Jia Kong from the Institute of Photonic Sciences in Spain (ICFO).
"You must think that 1 ms is a very long time for the atoms, long enough for about 50 random collisions to occur. This clearly shows that the entanglement is not destroyed by these random events. This is maybe the most surprising result of the work."
Whereas most quantum entanglement experiments use ultra-low temperatures, to keep interference like these collisions down to a minimum, this study – using rubidium metal and nitrogen gas – shows that entanglement can survive much hotter temperatures.
If we're going to be able to use this phenomenon in next-generation communication systems and quantum computers, we need to get it working in warmer, noisier environments, and that's something this new research points the way to.
One of the ways these findings could be useful in the future is in magnetoencephalography or magnetic brain imaging, a process that uses similar hot, high-density atomic gases to detect magnetic fields created by brain activity. Entanglement could potentially make the technique more sensitive.
For now, though, scientists have learned more about the rules of quantum entanglement, and just what it can and can't withstand.
"This result is surprising, a real departure from what everyone expects of entanglement," says ICFO quantum physicist Morgan Mitchell.
"We hope that this kind of giant entangled state will lead to better sensor performance in applications ranging from brain imaging, to self-driving cars, to searches for dark matter."
The research has been published in Nature Communications.