How can I put the unitary matrix $$e^\frac{i\pi}{2}I$$ to the quantum circuit?

I don't know if it is belong to $$U3(\theta, \phi, \lambda), U2(\phi, \lambda), U1(\lambda)$$

Thanks a lot.


1 Answer 1


$I$ is the identity matrix. In a quantum circuit, it means "do nothing". You don't need to program it in. The global phase doesn't make a difference to this either.

  • 2
    $\begingroup$ FWIW you can add global phases in Qiskit, circuit = QuantumCircuit(1); circuit.global_phase = pi/2 $\endgroup$
    – Cryoris
    Sep 16, 2020 at 15:25
  • $\begingroup$ Thanks a lot, I know sth! $\endgroup$ Sep 16, 2020 at 17:36
  • $\begingroup$ $e^\frac{i\pi}{2}=i$, so it rotates the phase by 90${}^\circ$. $\endgroup$
    – peterh
    Sep 17, 2020 at 15:50

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