enter image description hereI am new to quantum computing. My circuit contains only one qubit, one Hadamard gate and an operation to measure the state of the qubit. So, as I understand, the qubit is in superposition state after doing through the H gate, and has a probability of 50% of being in both states 0 and 1. After I measure it, (as in we force it to get out of its wave-like state or superposition state),I always end up with an output of 1? Is not it supposed to be random (quantum randomness) ?

  • $\begingroup$ perhaps you could show your code? It's easier to help if we know exactly what you've tried to do! $\endgroup$
    – DaftWullie
    Feb 17, 2023 at 12:37
  • $\begingroup$ actually its not a code but only a visualition of these quantum gates on the q-sphere. I added a picture. thank you for your help $\endgroup$
    – Wiss
    Feb 17, 2023 at 12:57
  • $\begingroup$ What is the plus in a circle? $\endgroup$
    – DaftWullie
    Feb 17, 2023 at 13:30
  • $\begingroup$ its for changing the phase and state of the qubit $\endgroup$
    – Wiss
    Feb 17, 2023 at 14:14
  • $\begingroup$ Perhaps try first without those + operators. You can also try quirk to double check the results $\endgroup$
    – rhundt
    Feb 17, 2023 at 16:20

1 Answer 1


The problem comes from the fact the in simulation a measurement gate really measures. In other words, the result is either 0 or 1. Try to remove measurement and you will see 50:50 states 0 and 1. Then try to run your circuit on simulator. The result should be also 50:50, or very close to this distribution.

Note that you do not have to reset the qubit. At the beginning it is always in state 0. Moreover, two $X$ gates cancel each other, so you can remove it. To change the phase of your state, use only one negation.

  • $\begingroup$ okey i understand thank you very muuch!! $\endgroup$
    – Wiss
    Feb 18, 2023 at 9:54
  • $\begingroup$ @Wiss: you are welcome. Could you please accept my answer provided your problem is solved? Thanks. $\endgroup$ Feb 18, 2023 at 11:25

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