Macroscopic quantum phenomena

Macroscopic quantum phenomena are processes showing quantum behavior at the macroscopic scale, rather than at the atomic scale where quantum effects are prevalent. The best-known examples of macroscopic quantum phenomena are superfluidity and superconductivity; other examples include the quantum Hall effect, Josephson effect and topological order. Since 2000 there has been extensive experimental work on quantum gases, particularly Bose–Einstein condensates.

Between 1996 and 2016 six Nobel Prizes were given for work related to macroscopic quantum phenomena.^[1] Macroscopic quantum phenomena can be observed in superfluid helium and in superconductors,^[2] but also in dilute quantum gases, dressed photons such as polaritons and in laser light. Although these media are very different, they are all similar in that they show macroscopic quantum behavior, and in this respect they all can be referred to as quantum fluids.

Quantum phenomena are generally classified as macroscopic when the quantum states are occupied by a large number of particles (of the order of the Avogadro number) or the quantum states involved are macroscopic in size (up to kilometer-sized in superconducting wires).^[3]

^ These Nobel prizes were for the discovery of super-fluidity in helium-3 (1996), for the discovery of the fractional quantum Hall effect (1998), for the demonstration of Bose–Einstein condensation (2001), for contributions to the theory of superconductivity and superfluidity (2003), for the discovery of giant magnetoresistance (2007), and for theoretical discoveries of topological phase transitions and topological phases of matter (2016).
^ D.R. Tilley and J. Tilley, Superfluidity and Superconductivity, Adam Hilger, Bristol and New York, 1990
^ Jaeger, Gregg (September 2014). "What in the (quantum) world is macroscopic?". American Journal of Physics. 82 (9): 896–905. Bibcode:2014AmJPh..82..896J. doi:10.1119/1.4878358.

[1] These Nobel prizes were for the discovery of super-fluidity in helium-3 (1996), for the discovery of the fractional quantum Hall effect (1998), for the demonstration of Bose–Einstein condensation (2001), for contributions to the theory of superconductivity and superfluidity (2003), for the discovery of giant magnetoresistance (2007), and for theoretical discoveries of topological phase transitions and topological phases of matter (2016).

[2] D.R. Tilley and J. Tilley, Superfluidity and Superconductivity, Adam Hilger, Bristol and New York, 1990

[3] Jaeger, Gregg (September 2014). "What in the (quantum) world is macroscopic?". American Journal of Physics. 82 (9): 896–905. Bibcode:2014AmJPh..82..896J. doi:10.1119/1.4878358.

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