HELSINKI, FINLAND — Researchers at Aalto University have built the world’s first cyclic quantum heat engine, a device so small and so cold that it runs on heat near absolute zero — the coldest temperature physically possible — and converts that heat into useful work.

For decades, engineers dreamed of an engine that could help power a quantum computer. What they got is an engine that is too cold to warm a cup of coffee, too small to see with the naked eye, and, by all accounts, absolutely thrilled about it.

The device, described in Nature Communications, uses a transmon qubit, a resonator, and a tunable quantum-circuit refrigerator operating near absolute zero. It implements something called an Otto cycle — the same basic thermodynamic principle that runs your car, except your car is not trying to compute the meaning of existence while doing it.

“It’s the most useful thing ever built that is, technically, freezing,” said Dr. Elina Virtanen, a physicist at the university who was not involved in the study but was reached by phone while standing next to a much warmer radiator. “At these temperatures, the engine doesn’t waste heat. It barely has any.”

"It's the most useful thing ever built that is, technically, freezing."

The engine’s breakthrough is that it operates autonomously in the superconducting circuits used in quantum computers, converting heat leakage into work instead of letting it corrupt delicate quantum states. Future versions could run inside quantum computers themselves, potentially unlocking far larger machines.

Scientists have been careful to note that the engine will not, at this time, power anything a human would recognize as useful — no laptops, no toasters, no electric scooters. But that, they say, is precisely the point.

“When a normal engine produces work, it gets hot,” explained Dr. Markus Lindqvist, a member of the research team. “When this engine produces work, it gets slightly less cold. It’s a revolution, if you think about coldness as a resource.”

INSIDE THE QUANTUM OTTO CYCLE

  • Step 1: Start at absolute zero, give or take a few millikelvins.
  • Step 2: Add heat. There is barely any. That's fine.
  • Step 3: Do work. The work is also barely any. Also fine.
  • Step 4: Repeat, forever, without ever once making a human comfortable.
  • Efficiency rating: better than your car, colder than your ex.

Some skeptics have asked what good an engine is if it cannot warm anyone’s hands. The answer, researchers say, is that the engine is not for warming hands. It is for running quantum computers, which are also not for warming hands. Science, it turns out, is a team sport with very specific job descriptions.

At press time, the research team was reportedly investigating whether the engine could power a tiny quantum toaster, “just to see what happens.”