"""Quantum state vectors The quantum state of :math:`n` quantum bits is represented as a 1D array of complex numbers of length :math:`2^n`; the components of the state vector in the computational basis. The computational basis for :math:`n` qubits is ordered by the number represented by the associated classical bitstring. """ import numpy as np __all__ = ["from_classical"] # type: ignore def from_classical(bitstring): """Return a quantum state corresponding to a classical bitstring. Parameters ---------- bitstring : sequence of bits Can be a string like "01011", or a sequence of integers. Returns ------- state : ndarray[complex] The state vector in the computational basis. Has :math:`2^n` components. """ bitstring = "".join(map(str, bitstring)) n = len(bitstring) try: index = int(bitstring, base=2) except ValueError: raise ValueError("Input is not a classical bitstring") from None state = np.zeros(2 ** n, dtype=complex) state[index] = 1 return state

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