----------------------------------------------------------------
Each Qbit is in C^2.
k-fold tensor is in C^{2^k}.

|binary> =
|b>|i>|n>|a>|r>|y> =
 [u]
 [n]
 [a]
 [r]
 [y]

|101> =
[0]
[0]
[0]
[0]
[0]
[1] <-- slot 5
[0]
[0]

 0   1
|0> |1>
 =   =
[1] [0]
[0] [1]

 0    1    2    3
|00> |01> |10> |11>
 =    =    =    =
[1]  [0]  [0]  [0]
[0]  [1]  [0]  [0]
[0]  [0]  [1]  [0]
[0]  [0]  [0]  [1]

  0     1     2     3     4     5     6     7
|000> |001> |010> |011> |100> |101> |110> |111>
  =     =     =     =     =     =     =     =
 [1]   [0]   [0]   [0]   [0]   [0]   [0]   [0]
 [0]   [1]   [0]   [0]   [0]   [0]   [0]   [0]
 [0]   [0]   [1]   [0]   [0]   [0]   [0]   [0]
 [0]   [0]   [0]   [1]   [0]   [0]   [0]   [0]
 [0]   [0]   [0]   [0]   [1]   [0]   [0]   [0]
 [0]   [0]   [0]   [0]   [0]   [1]   [0]   [0]
 [0]   [0]   [0]   [0]   [0]   [0]   [1]   [0]
 [0]   [0]   [0]   [0]   [0]   [0]   [0]   [1]

----------------------------------------------------------------
X_i = I (x) ... (x) ... X (x) ... I (x) ... I:
k-fold tensor with X in the ith slot.

----------------------------------------------------------------
(!!!) Entangled simply means non-simple (indecomposable) tensor. :)

Unitary = norm-preserving (prb 1 maps to prb 1) and linear.

----------------------------------------------------------------
Measurement (along with X) for state preparation of *input*.

Measurement as *output*.

----------------------------------------------------------------
Nothing here about time evolution of states -- ?!?