Ultracold Gases: Quantum Phenomena at Macroscopic Scales

By Dean Johnstone

In physics, it is common to expect the emergence of quantum effects at microscopic scales. Atoms and subatomic particles can behave both as a classical particle and quantum matter wave in accordance to Wave-particle duality. As such, all particles have a corresponding de-Brogile wavelength which depends on the mass and velocity of the particle. This wavelength can effectively be viewed as the spatial extent of the probabilistic, wavelike nature. Consequently, the small masses associated with microscopic particles means that their de-Brogile wavelength is sufficiently large compared to macroscopic objects, hence reflecting the appearance of quantum properties. For comparison, the de-Brogile wavelength of a snooker ball is about


times smaller than an electrons de-Brogile wavelength when moving at the same speed, which explains why objects above and at the macroscopic scale (visible to the eye) do not act in a quantum manner and interfere or diffract with one another.

However, as it turns out, collective quantum effects from a gas of Ultracold Atoms can in fact behave as quantum matter waves at macroscopic scales. A gas of atoms near absolute zero can effectively act as a single, giant quantum atom. This macroscopic object can then be manipulated to emulate the structure of crystals with light, fabricate an ideal quantum simulator or even generate artificial black holes in laboratories.


In this article, we shall discuss some of the important differences between classical and quantum particles before turning our attention to a gas of cold atoms. From there, we will then talk about the history and important properties of Ultracold Gases, before concluding with some of the most significant applications they hold within Physics and Technology.

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