Hot tea cools down, and ice cream melts — heat always flows from warm to cold, and this law seemed unbreakable. But in the quantum world, even familiar rules can be rewritten. Physicists placed a tiny mechanical resonator (a vibrating bridge the size of a microbe) in an optical cavity between two mirrors. A laser beam reflecting inside pushes on the resonator and makes it vibrate in a special way — creating an optomechanical coupling.
Using this, they applied quantum squeezing. In its normal state, the resonator vibrates chaotically, like a pendulum jolted in all directions by thermal kicks. Squeezing removes excess motion: vibrations become more predictable in one direction but more spread out in another. It's like a balloon: squeeze it from the sides, and it stretches upward. This squeezing breaks the symmetry of phase space — the mathematical landscape where every state of the system is marked by coordinates. As a result, heat flow is no longer rigidly tied to temperature differences.
The key finding is the link between heat reversal and quantum discord (a measure of purely quantum correlations stronger than classical ones). When correlations peak, heat flows against the gradient. This isn't just a trick but a new tool: active heat control at the micro level. In the future, such systems could cool hot spots in quantum processors or serve as elements of thermal logic circuits, where phonons, quanta of sound, carry signals instead of electrical ones. And then the familiar image of cooling tea becomes a technology where heat itself chooses where to flow.
Phonons are quanta of sound in solids. They carry heat much like photons carry light, but much slower and with greater losses.
In Peter Watts's novel Blindsight, alien creatures use thermal signals instead of neural impulses — perhaps the first steps toward such technologies have already been taken.