The connection between physical qubits of IBM devices are all bidirectional or there are some architectures that there existing some unidirectional connection?
I found that in IBM Quantum experience, all the device connections are bidirectional, I was wondering if there are some exceptions?


1 Answer 1


All of the backends are bidirectional from the viewpoint of Qiskit. The Cross-Resonance (CR) gate used in implementing the CNOT has a natural preferred direction associated with it, but accounting for the direction is done automatically by the devices, thus yielding a bi-directional topology.

  • $\begingroup$ Thanks! I saw the architecture of QX2 and QX3, and both of them are unidirectional. Are the two architectures still used currently? If we want to design a mapping ourselves, do we need to consider of the direction? $\endgroup$
    – peachnuts
    Feb 4, 2020 at 21:30
  • $\begingroup$ Qx2 has been updated and is now bidirectional. Qx3 is offline but similar to Melbourne which is also bidirectional now. $\endgroup$ Feb 4, 2020 at 21:31
  • $\begingroup$ I see. Thanks!! $\endgroup$
    – peachnuts
    Feb 4, 2020 at 21:36

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