``n x 1`` `sympy.Matrix` representing the `i`'th eigenstate of an
    `n`-dimensional Hilbert space (`i` >= 0)

def basis_state(i, n):
    """``n x 1`` `sympy.Matrix` representing the `i`'th eigenstate of an
    `n`-dimensional Hilbert space (`i` >= 0)"""
    v = sympy.zeros(n, 1)
    v[i] = 1
    return v