How does a quantum computer work?

In a few years, quantum computers will completely change the field of computing. Through the direct use of the laws of quantum physics, they will be able to multiply the capabilities and uses of a conventional computer. For Thierry Breton, CEO of the Altos group, their development will even represent a decisive “technological breakthrough”. Indeed, since the development of the first small quantum computers in the 1990s, scientists have made tremendous progress in the field. In March 2018 in particular, the unveiling of Google’s latest quantum processor, Bristlecone, takes a step closer to what is known as “quantum supremacy”. Thanks to all these recent advances, quantum computers are now becoming a must-have technology of the future. The finding: our computers have limited capabilities The computers we use today operate on the basis of a binary system: they encode the information in bits. While this has worked well for many years, this system is now starting to show some limitations in terms of storage and information processing. Even supercomputers, which have already pushed the boundaries of science, can be overwhelmed by the complexity of some operations. As Vincent Rollet explains in an article for the Pandora Institute, it’s because they simply do not “think” in the right way. Scientists have therefore been planning for some years to create machines with a completely different function. How it works ? In order to carry out complex operations, quantum computers will use the properties of quantum mechanics. Their processors operate thanks to two phenomena: superposition and quantum entanglement, which take place on a microscopic scale. “Instead of using bits […] the quantum computer uses quantum bits, or qbits, which do not take as value 0 or 1, but a superposition of 0 and 1”, explains Vincent Rollet . The use of qbits, described for the first time in a study in 2009, makes it possible to increase the storage capacity and speed of calculation of these computers exponentially. But because of this, they present the same limits as those of quantum mechanics. The phenomenon of “decoherence”, in particular, leads to the destruction of quantum objects at the end of the measurement. Overcoming obstacles to 2020 As Futura Sciences explains, scientists are therefore looking for solutions to overcome these physical obstacles. And since quantum processors can only be executed in very cold environments, protected from shocks and sounds, their study is both expensive and complex. However, in recent years, the digital giants have embarked on the quest for quantum computers, and their massive investments point to rapid progress. For now, Google seems to be leading the competition with Bristlecone, its quantum processor of 72 qbits unveiled on March 5, 2018. It is the most powerful to have been created so far; and researchers at the Quantum AI lab have predicted that they will soon be able to outperform supercomputers. Its fiercest competitor, IBM, remains in the running with its processor running at 50 qbits. Xavier Vasquez, technical director of IBM France, also said that their progress should lead to the creation of the universal quantum computer over the next decade. Prospects for revolutionary applications Beyond mathematical resolution and super-computing, these quantum computers can be used in many fields. On its website, IBM has listed some of their intended applications in the future. According to the firm, they will allow revolutionary advances in the field of medicine, bioinformatics, and artificial intelligence; but also in other more surprising sectors. Indeed, these calculators could be used to anticipate climatic and even financial crises more precisely, and thus to better prevent their consequences. For the moment, these complex machines remain destined for the field of research. However, according to Mikhail Lukin, Harvard physics professor, they will eventually make their entry into our daily life – and this faster than we think. The problem: it can go wrong As Wired explains, the development of these quantum computers could become “the big risk of the future”. If they keep pushing the limits of science, they can also weigh on …


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