A quantum state that lasts forever may finally be within our grasp

In quantum states that theoretically last forever, particles get bounced around again and again, as if in a hall of mirrors Guy Bell/Alamy; Yayoi Kusama, Infinity Mirrored Room They say nothing lasts forever – but, hey, what do they know? Sure, the passing years soften the carvings on statues, pigments on paintings flake with age, and even the most formidable fortresses collapse eventually. But those are all features of the human-scale world. Things tend to work a touch differently in the quantum realm. For nigh on 70 years, physicists have been chasing the dream of quantum eternity: an arrangement of atoms positioned so that the quantum states between them are frozen forever, like light bouncing in a never-ending hall of mirrors. Proving that such a thing could exist wouldn’t just be an incredible scientific milestone, it would also be very handy indeed. Quantum states that last forever – or even just for a very long time – could enable us to create completely new states of matter, some of which could be the basis of powerful new quantum computers. “It would open up a whole new class of phases that are otherwise impossible,” says mathematical physicist Wojciech De Roeck at KU Leuven in Belgium. We’ve glimpsed the secret quantum landscape inside all matter There is, however, a good reason why eternity has always seemed elusive. Thermodynamics, one of the central pillars of modern theoretical physics, insists that the fine details of things are always, eventually, smudged away. And until recently, physicists’ efforts to study quantum eternity had only served to underscore this seemingly unavoidable truth. Now, however, things seem to be changing and powerful experiments are hinting that eternity may not be out of reach. One of the rules that governs reality is that things tend to get messier over time unless energy is expended to intervene. This is a truism in life generally, but it is also a key assumption that underpins thermodynamics, the physics of heat, work and energy. It explains why pouring milk into coffee turns our cup a creamy, uniform beige, even without stirring. More broadly, the theory says that all systems eventually thermalise, meaning the different parts of things mix into averages. Based on this, you would think that nothing could endure forever. But in 1958, physicist Philip Anderson suggested a striking possible exception in the world of materials. To get your head around it, picture the inside of a material as a grid of different kinds of atoms that can be more or less ordered.