Diamond and algorithm allow quantum computers to cool themselves

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The rise of quantum computers is far from over. The problems posed by quantum physics in relation to its application in computing find few solutions, and researchers admit that they do not fully understand what is going on inside these computers of the future. One challenge, in particular, is the cooling necessary to run them. In fact, the latter (at least for the standard structure) depends on interactions between cold atoms, requiring an environment that is maintained at a temperature close to absolute zero. Researchers at the University of Stuttgart seem to have circumvented this problem by allowing a quantum computer to cool down even while it is performing calculations.

While classical computers reach the end of the performance that can be achieved with their microprocessors and binary data (0 and 1) called “bits,” their quantum version uses “qubits,” a part that exploits properties of quantum physics to power them. Thanks to this, qubits can be in two states simultaneously (in the state of superposition), which makes it possible to reconcile states 0, 1, or both at the same time, providing more possibilities. In other words, quantum computers will make it possible to perform extremely complex calculations, which cannot be done with current machines, at an unparalleled speed.

However, the power of a quantum computer depends not only on the number of qubits embedded in it. The quality of the superconductors that make up them is also critical. It should be known that qubits can spontaneously change their quantum state after perturbations caused by thermal energy, or any other perturbation in their environment. This phenomenon is known as “decoherence”. If this happens before the algorithm has finished running, the result will be a cluttered mess – not the result of an arithmetic operation – because any information stored in qubits is lost. Like a traditional computer restarting every second, it would be impossible to use it.

This is why today’s quantum computers use a highly advanced cooling system that allows them to operate at temperatures close to absolute zero (-273.15 degrees Celsius). At a very low temperature, the internal energy of the system is minimal – the atoms are almost frozen. Therefore, the probability of spontaneously changing the state of a qubit is much lower. This type of system has many drawbacks, particularly the need for space (volume) and output power.

Recently, Eric Lutz and colleagues at the University of Stuttgart, Germany, built a self-cooling quantum computer out of imperfect diamond by performing a series of computations, a “simple” algorithm. Their study was published in the journal physical review messages.

minus diamond

In recent years, qubits have been made from a number of isolated systems that remain consistent while the algorithms are running. These include trapped ions (atoms to which an electron is removed or added), ultra-cold Rydberg atoms and photons (particles of light).

On this basis, the researchers built their computer from imperfect diamond (which is minus two carbon atoms). They replaced one of these atoms with a nitrogen atom and left an empty space, called a void, in place of the other. We should know that the quantum state of a qubit is the spin of a single electron coming from an atom confined to a semiconducting structure. The spin is similar to the magnetic direction of the electron.

To manipulate each qubit, the researchers subjected them to microwaves. Thus they modified the spin of the nuclei of a nitrogen atom or the nuclei of two carbon atoms near the void. Each state has a certain amount of energy. By arranging them in a specific sequence (organized by an algorithm), researchers can use them to alter the power and cooling of a computer.

In order to find the best algorithm, the one that cools the system as much as possible, the scientists evaluated the algorithm’s ability to reduce computer power, not the ability to process information.

Unlike bulk quantum tires that require energy-intensive cooling, the diamond-based quantum technology can operate at room temperature, allowing it to be used in a variety of real-world environments. Indeed, starting and cooling qubits at room temperature by algorithm modification is a practical and important advantage for quantum computers in the future.

Moreover, this process provides high quality, stable qubits and is less affected by ambient noise. Diamond technology uses a hybrid combination of physical properties derived from quantum mechanics systems, rather than the magnetic properties used only by other quantum technologies, helping to reduce errors.

The optical table on which a quantum computer, made of specially designed diamonds, can cool itself. © Durga Dasari / University of Stuttgart

Larger quantum computers at room temperature

Last May, the Pawsey Supercomputing Research Center in Australia demonstrated the first room-temperature diamond-based quantum computer developed by Quantum Brilliance, an Australian-German company for quantum computing devices. Quantum Brilliance processors are expected to be the size of a graphics card, reaching 50 qubits by 2025, said Mattingly Scott, CEO. It is also intended to create a single-chip quantum accelerator. Add : ” Then you can install thousands of them in your data center and you have many of them [nœuds] From quantum coherence to massive balancing of quantum computations The startup is also studying which algorithms are more suitable for more parallelism.

The authors of this study now aim to incorporate their technology into larger computers, which are also algorithmically cooled and can, in fact, perform more complex computations than current quantum computers. The latter requires huge systems to cool them, and the risk of errors is high. As Landry Bretheau, Professor of Quantum Physics at the École Polytechnique de Paris, describes in an article: Today’s quantum computers look like large tin cans suspended from the ceiling, cooled to near absolute zero, from which hundreds of cables hang. “.

Source: Material review letters

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