The question is pretty simple. How can I get an input qubit $|0⟩$ in the state, say $$\cos{\frac{\pi}{10}}|0⟩ + \sin{\frac{\pi}{10}}|1⟩$$ Or any other sine/cosine mix state? Which gates do I need to use?


  • $\begingroup$ What gates do you have available? $\endgroup$ – DaftWullie Mar 27 at 6:10

$$R_y(\theta) = e^{-i\frac{\theta}{2}Y} = \begin{bmatrix} \cos\frac{\theta}{2} & -\sin\frac{\theta}{2} \\ \sin\frac{\theta}{2} & \cos\frac{\theta}{2} \end{bmatrix}$$

This gate might be named slightly differently depending on the source; Wikipedia doesn't seem to know it but this primer on rotations on Bloch sphere lists all rotation gates nicely.

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  • $\begingroup$ Just to add, on IBM Q the gate $R_y$ is implemented, you can also use $U3$ gate with parameters $\phi = \lambda = 0$ giving y-rotation. $\endgroup$ – Martin Vesely Mar 27 at 5:17
  • $\begingroup$ Thanks for your help Mariia and Martin. It means a lot! $\endgroup$ – Annonymus Mar 27 at 18:10

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