Quantum computers made from imperfect diamonds could stop themselves from overheating just by running an algorithm. Most quantum machines must be kept at low temperatures, but 鈥渁lgorithmic cooling鈥� might allow quantum computers to perform well at room temperature in the future.
Conventional computers slow down as they warm up, and quantum computers can even stop working if they get too hot. While classical computers are typically cooled by fans, quantum computers generally require much greater cooling than fans could provide
Eric Lutz and his colleagues at the University of Stuttgart in Germany built a small, diamond-based quantum computer that can cool itself by performing a sequence of mathematical operations.
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Their computer consists of three qubits, or quantum bits, in a diamond that is missing two carbon atoms. They replaced one of these atoms with a nitrogen atom and left an empty space, known as a vacancy, where the other one had been.
To manipulate each qubit, the researchers blasted them with microwaves. This changed the spin of either the nitrogen atom鈥檚 nucleus or the nuclei of two carbon atoms close to the vacancy. These manipulations act as logic gates, the basic building blocks of calculations the computer performs, and alter the quantum state of a qubit. Each quantum state has a specific amount of energy, so a sequence of gates can be used to change the computer鈥檚 energy and cool it.
The researchers found that their algorithmic cooling was exceedingly close to the theoretical limit of maximum cooling efficiency.
鈥淲e tested and evaluated the performance of an algorithm, but by the performance standards of a refrigerator,鈥� says team member . In other words, instead of assessing how successful the algorithm was at processing information, it was graded based on how well it lowered the computer鈥檚 energy.
at the University of Exeter in the UK says it is important that the researchers developed a theoretical model for their computer in addition to their successful experiment, as even seemingly simple ideas like how temperature is defined can change at the quantum level.
鈥淲e can talk about quantities like temperature and efficiency, but we have to make sure that they actually make sense for the system we have,鈥� he says. Lutz says that his team鈥檚 mathematical analysis is significantly more comprehensive and detailed than previous theories of similar experiments.
Team member says that for many quantum computer designs, such as those involving superconducting circuits, the whole machine must be kept in a refrigerator from the beginning. So starting with room-temperature qubits and cooling them by tweaking an algorithm is a practical 聽advantage of diamond-based quantum computers, he says.
This type of quantum computer can execute many of the same calculations as quantum machines with other designs, so the researchers鈥� next step is to try to make their algorithmically cooled computer bigger and use it for more complex calculations.
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