Quantum Bits for a New Quantum Age

The beginnings of a new quantum age lie in the "weird quantum situation" that Boris Podolsky, Nathan Rosen and Albert Einstein described in their famous 1935 paper. Alain Aspect (Institut d'Optique, Palaiseau, France), 2010 Wolf Prize winner, presented a colloquium at ICTP on 20 August 2013, giving the audience insight into how Einstein and his co-authors' ideas led to the exploration of the concept quantum entanglement, which then laid the foundation for quantum information, after the conceptual breakthrough of John Bell and his famous inequalities established in 1965.

In simple terms, quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described globally, even if the individual objects may be separated in space-time.

"In his lectures of physics, in the late 1950s, [Richard] Feynman wrote that all the mystery of quantum mechanics is wave particle duality. But, 25 years later, in 1982, he changed his mind and recognized that there is something else mysterious in quantum mechanics and that is entanglement," says Aspect, a leader in experimental work on quantum entanglement. Feynman's acknowledgment of this even more extraordinary property led to his proposal of the idea of quantum simulation and quantum computing, according to Aspect.

In 1964, physicist John Bell's theorem showed that the worldview of Einstein is not enough to describe the concept of entanglement. "The work by Bell is very important," says Aspect. "Before Bell, people had a feeling that understanding entanglement was only a matter of interpreting quantum mechanics without any practical consequence."

Bell's theorem has allowed experimentalists to show that the concept of quantum entanglement is a reality, and based on this concept, the field of quantum information has emerged, where one uses quantum bits or "qubits". In principle, entanglement between qubits can enable new methods for processing and transmitting information in faster ways.

"As of today, nobody knows if we will eventually succeed in building a quantum computer. But, if we do it will be a new revolution in society, just like the industrial revolution of the 19th century or the recent information technology revolution brought about by lasers, optical fibres and computers," Aspect points out.