# Is there an error on Qiskit.org textbook with the superdense coding section?

The textbook on Qiskit.org has

When the H-gate is applied to first qubit, it creates superposition and we get the state $$|0+\rangle = \frac{1}{\sqrt{2}}(|00\rangle + |01\rangle)$$

Shouldn't it be: $$|0+\rangle = \frac{1}{\sqrt{2}}(|00\rangle + |10\rangle)$$

as explained in some answers here: (How do I apply the Hadamard gate to one qubit in a two-qubit pure state?)

• Hi and welcome to Quantum Computing SE. Please use TeX notation for math instead of screenshots. Jan 13, 2021 at 8:38

Qiskit's coding of the qubits is made such that Qiskit's least significant bit has the lowest index (0) and will be written at the right of the state, so instead of writing a qubit like $$|q_0 q_1 ... q_n \rangle$$, it will rather be $$|q_n q_{n-1} ... q_0 \rangle$$, explaining the difference between the Qiskit explanation and the explanation from the question you pointed. The first qubit is on the far right, so Hadamard will be applied on the one in the far right, thus you have the first result you pointed.