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Hi, I haven't posted for a while. I've seen this topic come up a few times, but it always seems to me that a few points aren't made clear. Can I just check the following is true?
1) The state space of a quantum system is always an infinite-dimensional seperable Hilbert space i.e. a Hilbert space with a countably infinite Hilbert dimension.
2) An infinite-dimensional seperable Hilbert space is an uncountably infinite-dimensional vector space (i.e. has an uncountable Hamel dimension).
3) Sometimes though subspaces of finite dimension may contain most of the relevant information (e.g. when talking about 'qubits'), so the conceit that the state space is a finite dimensional Hilbert space is used.
4) Sometimes the opposite conceit is presented, i.e. that the state space is a non-seperable Hilbert space (e.g. when describing the eigenstates of an obseravble with a continuous spectrum). In actuality the state space is still seperable, but an implicit reference is made to a non-seperable Hilbert space which 'looks' a bit like it should be the state space.
A related question, what *exactly* is the problem with non-seperable Hilbert spaces?
Thanks
1) The state space of a quantum system is always an infinite-dimensional seperable Hilbert space i.e. a Hilbert space with a countably infinite Hilbert dimension.
2) An infinite-dimensional seperable Hilbert space is an uncountably infinite-dimensional vector space (i.e. has an uncountable Hamel dimension).
3) Sometimes though subspaces of finite dimension may contain most of the relevant information (e.g. when talking about 'qubits'), so the conceit that the state space is a finite dimensional Hilbert space is used.
4) Sometimes the opposite conceit is presented, i.e. that the state space is a non-seperable Hilbert space (e.g. when describing the eigenstates of an obseravble with a continuous spectrum). In actuality the state space is still seperable, but an implicit reference is made to a non-seperable Hilbert space which 'looks' a bit like it should be the state space.
A related question, what *exactly* is the problem with non-seperable Hilbert spaces?
Thanks