If computers heat up too much, they can stop functioning. A new type of quantum computer, made of processed diamonds, can cool itself by performing calculations.
Quantum computers made of processed diamonds can protect themselves from overheating. They do this by executing a certain algorithm. Currently, most quantum computers still have to be stored at low temperatures. With this ‘algorithmic cooling’ they could also function at room temperature in the future.
Like regular computers, quantum computers slow down as they warm up. If they get too hot, they can even stop functioning. Ordinary computers are usually cooled by fans. However, quantum computers generally require much more cooling than fans can provide.
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Time will tell
Refrigerator standards
physicist Eric Lutz and his colleagues at the University of Stuttgart therefore built a small, diamond-based quantum computer that cools itself by performing a series of mathematical operations. Their computer consists of three qubits, or quantum bits, placed in a diamond that lacks two carbon atoms. The researchers replaced one of these atoms with a nitrogen atom. The place of the other atom remained empty.
To control the qubits, the researchers bombarded them with microwaves. This changes the spin — a property of particles that you can think of as their spin — of either the nucleus of the nitrogen atom or the nuclei of two carbon atoms that are close to the void. These manipulations act as logic gates, the basic building blocks of the computer’s calculations. They change the quantum state of a qubit. Each quantum state has a specific amount of energy, so a series of gates can change the computer’s energy. As a result, it cools down.
The researchers found that their algorithmic cooling is very close to the theoretical limit of maximum cooling efficiency. “We tested and evaluated the performance of an algorithm, but according to the standards of a refrigerator,” says team member Rodolfo Soldati† In other words, instead of judging how successful the algorithm was at processing information, it was rated based on how well it lowered the computer’s power.
Practical advantage
Quantum physicist Luis Correa of the University of Exeter in the United Kingdom calls it important that the researchers have also developed a theoretical model for their computer in addition to their successful experiment. This is necessary, because even seemingly simple ideas such as the definition of temperature at the quantum level can be different. ‘We can talk about parameters like temperature and efficiency, but we have to make sure that they really make sense for the system we have,’ he says.
Lutz says his team’s mathematical analysis is significantly more comprehensive and detailed than previous theories surrounding similar experiments. Team member Durga Dasaric says that many quantum computer designs, such as those involving superconducting circuits, require the entire machine to be kept in a refrigerator from the start. So starting with room temperature qubits and letting them cool down by an algorithm is a practical advantage of diamond-based quantum computers, he says.
This type of quantum computer can perform many of the same calculations as other quantum computers. The next step for the researchers is to make their algorithmically cooled computer bigger so that it can perform more complex calculations.