The 2 Quantum Revolutions in Technologies

39188583425_52e0f25bbb_k.jpgA Wafer of the Latest D-Wave Quantum Computers

1/ The Wave-particle duality

Single particle interference.

  • A particle (ex electron) also behaves as a wave
  • A wave (light) can also behave as a particle (single photon effect)

Classical models, (local realism à la Einstein) in ordinary space-time.

  • 1801, one of the most beautiful experiments in all physics, Young's interference experiment, also called Young's double-slit interferometer cf. Veritasium video
  • 1900/1905, the Ultraviolet catastrophe and the work of Plank (and then Einstein) allowed to bring to light the theory of emission of light packets (quantum) with the use of the famous Planck's constant (h)
  • 1924, Louis de Broglie had the idea of generalizing the principle.
  • 1963, For Richard P. Feynman, the whole mystery of quantum physics was there...

Young's interference experiment: commons wikimedia


It has allowed a better understanding of the structure of the material and exotic properties (as superfluidity, supraconductivity, Bose Einstein Condensate) which resulted in a deep understanding of how the electrical current conducts into the matter.


The greatest physicists offer us the laser, the transistor, the integrated circuits which it would be very difficult to do without nowadays since they are present everywhere in our daily lives.

2/ Quantum entanglement

  • Hanbury Brown-Twiss effect for particles
  • Hong-Ou-Mandel effect
  • Bell's inequalities violation

Interference in Hilbert space. No classical model in ordinary space time (hence the complexity of understanding the quantum mechanics).

  • 1935, Einstein, Podolsky and Rosen published a paper (EPR paradox) in response to Niels Bohr and Werner Heisenberg (Copenhagen interpretation) and to prove the incomplete nature of quantum mechanics.
  • 1964, John Stewart Bell wrote the famous Bell's theorem while at the base he wanted to bring additional elements to the EPR paradox.
  • 1982, Richard P. Feynman published Simulating physics with computers, considered as the founding article of quantum computer and quantum calculations, where he goes back to what he said in 1963.

Bell test experiments


Entangled particles, even far from each other, interact as a single object, described in an abstract mathematical space. The size of the mathematical space grows exponentially with the number of entangled particles making it impossible to describe it beyond a few dozen.

A good example to realize, it's the last news of the small war between Google and IBM on quantum supremacy. IBM explained that it could do the calculation in 3 days instead of 10,000 years (mentioned by Google) to resolve the quantum operation performed by Google's machine. But they omitted to mention that it would have needed all the RAM of the largest supercomputer in the world (an IBM with 250 Million Gigs of RAM) and that it would have been enough for Google if its 54th entangled Qbits were functional (only 53 of the 54 entangled Qbits of the processor was functional) to make this impossible and with only 7 entangled Qbits more, it would take 100 times more Ram to IBM to obtain the same result...

Associated with the control of the individualization of particles, this is what led to the 2nd quantum revolution.


Quantum computing but that's not all, there is Quantum simulators (that does not require ideal particles as Quantum computing) like Noisy Intermediate-Scale Quantum (NISQ) technologies which is very promising on optimization of resource (as electric power grid or quantum chemistry).

One of the most advanced results being the Quantum (cryptographic) Key Distribution (QuantumID by single photons, random number generator, continuous variable) and the Quantum network (teleportation with the best example by the team of Chinese scientists who have realized a satellite-based distribution of entangled photon pairs over 1,200 kilometers)

Main source Alain Aspect's conference, a French physicist who was the first to prove by experimentation (he performed the Bell test experiments cf. minutephysics video for a nice explaination) the reality of quantum entanglement (1980)


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