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QUANTUM computing
QUANTUM COMPUTING: PROMISES, ACHIEVEMENTS AND CHALLENGES
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Thomas AYRAL Eviden Quantum Lab, 78340 Les Clayes-sous-Bois, France thomas. ayral @ eviden. com
Quantum computers regularly make the headlines, with optimistic claims( often issued by companies large and small) alternating with pessimistic rebuttals( often by academic labs): sometimes they supposedly solve outstanding hard computational problems, sometimes their performances are dwarfed by classical machines. The goal of this article is to shed light on this back-and-forth, and explain what quantum computing could really be useful for.
https:// doi. org / 10.1051 / photon / 202513166
WHAT IS A QUANTUM COMPUTER? The term of quantum computer encompasses a large variety of physical implementations. All have in common the( more or less precise) manipulation of individual objects with quantum properties: the spin of electrons, the energy levels of atoms, the polarization of photons, or even current loops in electrical circuits. Most quantum computing systems are engineered so that only two states— usually called | 0
> and | 1— of these individual objects are
> reachable during a computation. What is quantum about these objects is that they can not only be in state | 0
> > or in state | 1( as would be the case for classical bits), but also in an arbitrary superposition of both:, with α and β two complex numbers.
More importantly, these two-level systems, usually called qubits( for quantum bits), can be coupled to one another by special operations: two neighboring atoms can be coupled via a van der Waals interaction, two electrical circuits by a capacitive coupling,
| ψ
> = α | 0 > + β | 0 >
66 www. photoniques. com I Photoniques 131