Ok so I saw this video by Brian Cox where he explains how no 2 particles can have same energy level.

Later I watched video "Was Brian Cox wrong?". Where they explained that he (probably on purpose) oversimplified it. And in fact it means that in fact no 2 particles can be in same quantum state. And that quantum state is defined by multiple properties.

So it sort of made me think. Quantum computer relies on certain quantum properties to operate, yeah? So if in order to perform some operation, some property need to be set to different state? And if that change would force it to enter to same quantum state as some other particle in universe? What would happen then?

Or another scenario if in order to maintain some state of machine, some particular particle has to stay in some particular quantum state. But at same time somewhere, some other particle tries to enter that state? Would that alter the particle in the machine, ruining it?

Or am I over simplifying things too much?

Sorry if this is a stupid question, I am not a physicist at all as yous may tell. It's just that video made me curious :)


1 Answer 1


For one, Brian Cox was probably talking about fermions and, more specifically, about identical fermions. Bosons, such as light, can share the same energy level and even the same quantum state. For example, in Bose-Einstein condensates, all the particles (i.e. atoms) share the same ground state energy level.

The simplification that you mention probably deals with the fact that many of the bosons physicists work with are composed of fermions. Bosonic atoms are made up of fermions (electrons, quarks) and bosons (photons, gluons, etc) and yet the atoms act like bosons. The Pauli exclusion principle does still apply to the constituents of the atoms but you have to look at the full wavefunction describing all the particles within all the atoms involved in a Bose-Einstein condensate to see it.

As for quantum computers, the particles involved in the computer are localized to the experiment, i.e. you don't expect to find your qubit orbiting the moon. The particles' positions, or more accurately the dependence of the particles' wavefunction on position, is part of its quantum state. So no, an arbitrary particle somewhere else in the universe cannot affect the quantum computer.... unless the particle is a meteor that is about to hit the quantum computer, in which case the calculation is toast.

No, it is not a stupid question. Keep on asking them.

  • $\begingroup$ I was typing my own answer, but then yours popped up, and I was so impressed I gave up on mine. :D $\endgroup$
    – Matt Scott
    Apr 22, 2013 at 1:00
  • $\begingroup$ The more points of view, the better, so please add your answer. Even if the answers say the same things, but in different ways, they both can help, $\endgroup$
    – Jason A
    Apr 22, 2013 at 1:10

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