Reversible computation and no cloning theorem in quantum computing
No-cloning theorem refers to creation of independent copies of a qubit. With CNOT gates you’ll only create mirrors.

For instance, if you have $\alpha \left| 0 \right&gt; + \beta \left| 1 \right&gt;$ and measure it, you’ll get 0 with probability $p_a=|\alpha|^2$ and 1 with $p_b=|\beta|^2$. Now if you clone this qubit and measure both, you should get 00 with probability $p_a^2$, 01 with $p_a p_b$, 10 with $p_b p_a$ and 11 with $p_b^2$.

Mirroring with CNOT gives a different picture: 00 with $p_a$, 11 with $p_b$ and zero probability for 01 and 10.