Gemini, the first consumer quantum computer

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Nuclear magnetic resonance for simplified quantum operation

On the other hand, and to be expected, Gemini is much less powerful, capable of processing only 2 qubits (a qubit being the quantum equivalent of a classical computer bit). It is based on an entirely different technology called “nuclear magnetic resonance”. This works by trapping specially selected molecules in a strong magnetic field, then channeling them with radiofrequency pulses to manipulate the spins of the atoms they contain.

L’informatique quantique progresse plus vite que jamais, notamment depuis que certaines architectures ne nécessitent plus des températures proches du zéro absolu pour fonctionner, certains chercheurs ayant notamment déclaré être sur la piste d’un modèle d’ordinateur quantique fonctionnant à température ambiante. Et plus récemment, voilà que le premier ordinateur quantique de bureau est proposé par une start-up chinoise. Il s’appelle Gemini, et sa nouvelle version sera vendue à moins de 5000 dollars selon l’entreprise.

La start-up innovante derrière ce projet est SpinQ Technology, basée à Shenzhen, en Chine. Ce nouveau modèle grand public et de taille réduite fait partie de sa gamme SpinQ, destinée aux écoles et à la recherche. L’année dernière déjà, elle avait mis en vente un ordinateur quantique « de bureau » pour environ 50’000 dollars. Cependant, en plus du prix très contraignant, ce dernier pèse 55 kg… Qualifier l’engin d’ordinateur de bureau est donc légèrement tiré par les cheveux.

Mais leur nouvel ordinateur quantique Gemini (la nouvelle version) est plus petit que jamais et surtout beaucoup moins cher. « Cette version simplifiée devrait être commercialisée au quatrième trimestre 2021, de sorte qu’elle puisse être plus abordable pour la plupart des écoles de la maternelle à la 12e année dans le monde », explique l’équipe de recherche. Le prix de la machine contraste fortement avec celui des ordinateurs quantiques commerciaux actuels, qui peuvent coûter environ 10 millions de dollars et traiter plus de 50 qubits. Les détails techniques du système ont été publiés sur le serveur arXiv.

Nuclear magnetic resonance for simplified quantum operation

On the other hand, and to be expected, Gemini is much less powerful, capable of processing only 2 qubits (a qubit being the quantum equivalent of a classical computer bit). It is based on an entirely different technology called “nuclear magnetic resonance”. This works by trapping specially selected molecules in a strong magnetic field, then channeling them with radiofrequency pulses to manipulate the spins of the atoms they contain.

After each series of radio pulses, the atoms relax and emit their own radio frequency signals, which reveal their new state. In this way, it is possible to reverse the spin of the atoms (which is equivalent to changing a 0 to 1 and vice versa) and to make the spins of neighboring atoms interact. This last step makes it possible to simulate mathematical operations, and finally to record the result.

The Gemini quantum computer (left) and the SPINQUASAR system home page (right). Gemini can connect to a personal computer through SPINQUASAR, which must be installed on the personal computer. SPINQUASAR provides an interface for users to easily configure and operate the quantum computer. © Shi-Yao Hou et al.

Le composé au cœur du fonctionnement de la machine est le diméthylphosphite, une molécule tétraédrique composée d’un atome de phosphore, d’un atome d’hydrogène, d’un oxygène et de deux groupes CH3O. Il se présente sous la forme d’un liquide incolore à température ambiante. Le diméthylphosphite est idéal, car les atomes de phosphore et d’hydrogène sont liés l’un à l’autre et sont suffisamment proches pour interagir tout en pouvant être manipulés indépendamment.

To ensure that the radio signals of the hydrogen and phosphorus atoms are strong enough to be picked up, a very large number of molecules is needed, about 10 15 . This in turn requires a few drops of liquid, placed in a small "vial" in the middle of the strong magnetic field.

This technique is well understood and has long been used for medical imaging. Indeed, the first quantum computers built in the 1990s used exactly the same approach. Back then, however, this approach was expensive, as magnetic fields strong enough to do the job could only be created by strong superconducting magnets. These had to be cooled to the temperature of liquid helium, a difficult task that required expensive and bulky equipment.

Permanent magnets instead of superconducting magnets

Instead of superconducting magnets, Gemini uses permanent magnets. Following the latest advances in the field, they can produce fields with a force of up to one Tesla, tens of thousands of times more powerful than the Earth's field. For quantum computing, the produced field must also be very regular. The team uses a technique called "shimming" for this, which generates another magnetic field capable of canceling out any irregularity in the base field, which is more powerful. The result is an extremely strong and even magnetic field.

To use Gemini, all you have to do is connect it to a regular computer with software capable of controlling it, called SPINQUASAR. Although it only processes 2 qubits, the device is capable of performing a number of quintessential quantum calculations. For example, it can implement a version of the Grover algorithm, which makes it possible to search a database faster than a conventional algorithm.

No more efficient than a conventional computer ...

However, if your goal is to acquire this machine in order to be in possession of the most powerful computer that you have ever had, you will be disappointed ... Indeed, with only 2 qubits, none of the algorithms that it can run will not perform better than a conventional computer. For most applications, researchers admit that Gemini does not even come close to a conventional last generation computer ... But the objective here is to demonstrate quantum computing and allow students to try it out. themselves.

Previously, the SpinQ team claims to have shipped their first Gemini model (the 55kg version) to institutions in Canada, Taiwan and China. But at $ 50,000 per unit, these places must be well equipped. That's why the company will launch this cheaper version based on the same platform later this year. Currently, she is also working on a more powerful system that will be able to handle 3 or 4 qubits. Enough to make search applications more interesting.

However, “mainstream” quantum computers like Gemini will never match the power of quantum computers from Google, IBM, Microsoft, and other computer giants. One of the major drawbacks of quantum computing based on nuclear magnetic resonance is that it cannot process more than a dozen qubits at the moment. Moreover, the question of knowing if this type of computation is really quantum is still the subject of a debate.

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