# Quantum Computing: The Quest For The Digital Grail

By making it possible to leverage current computing performance, quantum computing could be one of the solutions at the end of Moore’s Law.

The concept of the quantum computer was born in the 1970s and 1980s. It is notably worn by the American physicist David Wineland – who received the Nobel Prize in physics for his research in this field. Behind this concept is the idea that quantum phenomena could be used to increase the computing power of conventional machines. While today’s computers use the bit as the fundamental unit, the quantum calculator leans on a value called the qubit (or quantum bit). A value that allows not the only expression through 1 and 0, but also a superposition of both.

The speed of calculation is thus increased exponentially, the machine being able to simultaneously process several states at a time. The power measurement of the qubit? It is 2 to the power N (N being the number of qubits in the processor). Thus, a binary machine based on a 6-bit architecture could create one of the 64 (2 to the power 6) possible combinations (000000, 000001, 000010 …). The qubit can be a superposition of 1 and 0, can tend suddenly to 64 states. Quantum computing thus makes it possible to overcome the limits of Moore’s Law, according to which the complexity of entry-level semiconductors doubles every year at a constant price.

**How to go from bit to quit? That’s the question …**

But how is a qubit of information concretely presented? Very schematically, the functioning of a qubit (which can be compared to an artificial atom) is based on different phenomena of nuclear physics. This is also why the computer is said to be quantum. It refers to quantum physics describing the behavior of atoms and particles. What are these nuclear phenomena? A qubit can be created by relying for example on the polarization of a photon (and the measurement of the plane of polarization), or on the energy level of an atom, or the kinetic moments of “spin”, or revolution, the electron around him.

**A major obstacle: the system must remain isolated for the duration of the calculation**

There are several techniques for creating qubits. Thanks to the superconductors, they can be embedded on electronic circuits equipped with semiconductors manufactured from methods already known, borrowed from nanoelectronics.

Remains a major technical obstacle before operating a quantum computer. The system, during the calculation phase, must be totally isolated from any thermal or magnetic interference. Because of the nuclear physics that sets it to music, the qubit is indeed sensitive to any disturbance, including electromagnetic fields. Researchers call the time of “decoherence” the period during which the system thus remains isolated, the integrity of its quantum properties then being complete.

The design problems are also very numerous. Beyond the creation of a qubit, we must also be able to create detectors to measure the information carried by the qubit. This implies mastering the parameters of the magnetic flux (intensity and spatial distribution), which proves to be complex.

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Often openly criticized by the scientific community, some researchers, especially French, have imagined the next step. Simon Thorpe, CNRS research director at CERCO (Center for Research on Brain and Cognition) in Toulouse, does not hesitate to assert the existence of a link between consciousness and quantum physics, referring in particular to the work of American researchers Stuart Hameroff and Roger Penrose. From there to evoke a future quantum computer that would be endowed with the conscience … Simon Thorpe raises the question of this eventuality for the future (see his presentation on a conference given in 2013).