Bit indices reversed from bit_string_probabilities to measured

[rigetti]

Bit indices reversed from bit_string_probabilities to measured

[stylewarning]

No problem. I might add that this is a good convention to follow because, were we to do it left-to-right, the basis elements would change if you add a qubit to the system. The index of the |1> state in a 1-qubit system is the same as the index of the |0001> state in a 4-qubit system. In the left-to-right scheme, we would have |1> be indexed by 1, but |1000> be indexed by 8, which seems silly. :)

[stylewarning]

Hello! Thanks for the report.

The qubit indexes in Quil correspond to the exponents in the binary expansion of the basis index. Or, in other words, you should read the binary numbers right-to-left. So

X 0
X 1

would be the |011> state, because

011 (binary) = 3 (decimal) = 0*2^2 + 1*2^1 + 1*2^0

The exponents of the radix 2 are precisely the qubit indexes.

It is important to note that some sciences do use other conventions here, which is important to be mindful of when writing Quil.

[vontell]

Ah of course; thanks for the clarification!