A BEC is a matter of dilute gas of low densities called bosons cooled to temperatures close to absolute zero. Under such conditions, a large fraction of the bosons occupy the same quantum state, at which point quantum phenomena, like wavefunction interference become apparent macroscopically.
Theoretically nothing prevent the bosons from occupying the same location. The state is not perfectly localized, because their state is not exactly zero momentum. The HUP puts a lower limit on their localization.
What prevents bosons from occupying the same location?
It is possible to create a BEC of just photons, in this case they are using optical microcavity.
Can a system entirely of photons be a Bose-Einsten condensate?
We correspondingly expect a Bose-Einstein condensation when the
photon wave packets spatially overlap at low temperatures or high densities, i.e. the
phase space density 2
nth exceeds a value near unity. Here n denotes the number
density, photons per area, andth h/ 2mph kBT 1.58m (defined in analogy to e.g.
a gas of atoms17) the de Broglie wavelength associated with the thermal motion in the
Now you are asking about the number of photons in the condensate. In this case, they had 77000 photons.
At room temperature (T = 300 K), we arrive at 77000 Nc .