Quantum Mechanics

To Cool A Quantum Computer, You Need A Nanofridge

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Quantum computers could boost computing power exponentially, but right now, they're still in their infancy. Their revolutionary promise comes with a lot of loose ends, since a new form of computing requires new ways of making chips, transferring data, and cooling components. A group of researchers from Aalto University in Finland may have jumped that latter hurdle: they developed a nanoscale refrigerator designed to cool quantum bits.

The centimeter-sized silicon chip has two parallel superconducting oscillators and quantum-circuit refrigerators connected to them.

Do Not Disturb

Classical computers work with particles of information, or "bits," that each exist as either an 0 or a 1. The reason quantum computers could be so revolutionary is that quantum particles exist in superposition—that is, they can be 0, 1, and all points in between, and only when you measure them do they "decide" on a value. The ability to contain multiple values simultaneously gives them the ability to crunch a million computations at once.

But superposition ain't easy. The slightest interference can destroy that state of being many values at once, so quantum bits, or "qbits," must be shielded from all external disturbance—a computer fan, for instance. What's more, they require low temperatures to operate: qbits have to start in their ground states to run an algorithm, during which they quickly heat up. Unless you want to wait around a while, you'll need a quick and efficient way to cool them that won't disturb their quantum behavior.

Researcher Kuan Yen Tan conducting measurements in the Quantum Computing and Devices Labs at Aalto University.
Artist's impression of the quantum-circuit refrigerator in action. As an electron tunnels, it simultaneously captures a photon, which leads to cooling of the device.

Life In The Fast Lane

In May 2017, the Aalto team led by physicist Mikko Möttönen announced that they had developed just the thing. Their quantum-circuit refrigerator takes advantage of a phenomenon known as quantum tunneling, which lets a quantum particle pass through a barrier due to the fact that it functions as both a particle and a wave. As Michael Irving of New Atlas explains, "If there is an inducement for an electron to be on the other side of a barrier—such as more energy—it can, in a way, blink through the material to reach it."

The team's device is comprised of a superconducting channel and a non-superconducting channel divided by an energy gap. The superconducting channel is a "fast lane" that lets electrons move with zero resistance, while electrons in the non-superconducting channel move more slowly. Electrons want to be in the fast lane, but only those with enough energy to jump the gap can get there. Electrons without sufficient energy, then, can borrow some from a neighboring qbit. With energy comes heat, and as energetic electrons jump into the fast lane, they take heat with them, cooling the whole system down.

In this case, the researchers used superconducting resonators to stand in for qbits, so the next step is to use qbits themselves. Of course, the finicky nature of quantum particles is the reason no one has created a qbit fridge before, so moving to qbits will be no small feat—even turning off the device has the potential to destroy the superposition. But Möttönen is hopeful. "Maybe in 10 to 15 years, this might be commercially useful," he told New Scientist. If it's another step toward the quantum computing revolution, we're hopeful too.

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Key Facts In This Video

  1. Transistors can either block or open the way for bits of information to pass. 00:54

  2. Four classical bits can be in one of 16 different configurations at once; quantum qubits can be in all 16 combinations at once. 03:44

  3. Quantum computers could better simulate the quantum world, possibly leading to insights in medicine and other fields. 06:12