Note: Throughout this documentation, I'll refer to ket (lowercase) and Ket (uppercase). "Ket" refers to a type, while ket refers to a convenience constructor for a Ket with a single basis state. The same goes for bra and Bra.

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Constructing Single Kets

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To begin, let's make a single state using the ket function:

julia> ket(0)
Ket{KroneckerDelta,1,Int64} with 1 state(s):
  1 | 0 ⟩

As you can see, the ket function takes labels (in this case, a single zero) as arguments. In QuDirac, anything can be used as a Ket label - primitives, strings, composite types, etc. Simply pass the desired label in as we did 0 above:

julia> ket(":)")
Ket{KroneckerDelta,1,Int64} with 1 state(s):
  1 | ":)" ⟩

julia> ket(:a)
Ket{KroneckerDelta,1,Int64} with 1 state(s):
  1 | :a ⟩

julia> ket([1,2,3])
Ket{KroneckerDelta,1,Int64} with 1 state(s):
  1 | [1,2,3] ⟩

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Constructing Single Bras

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Bras can be constructed the same way using the bra function:

julia> bra(0)
Bra{KroneckerDelta,1,Int64} with 1 state(s):
  1 ⟨ 0 |

Just like Kets, Bra labels can be anything.

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Constructing Single Product States

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The number of labels passed to the ket/bra functions determines how many factors there are in the basis of the resulting state. For example, to construct | 0 ⟩ ⊗| 0 ⟩ ⊗ | 0 ⟩ we can simply do the following:

julia> k = ket(0,0,0)
Ket{KroneckerDelta,3,Int64} with 1 state(s):
  1 | 0,0,0 ⟩

julia> nfactors(k)
3

Just as with single-factor states, one is free to use labels of any type:

julia> k = ket(0, ":)", :a, [1,2,3])
Ket{KroneckerDelta,4,Int64} with 1 state(s):
  1 | 0,":)",:a,[1,2,3] ⟩

julia> nfactors(k)
4