Unitary folding methods does not work for sx gates (Qiskit)

[amrit-11]

SX gates are part of the native gate set that are implemented by IBMQ devices, but when I try to scale errors by unitary folding using fold_global method or even folding from left or right, it throws the exception:

QasmException: Unknown gate "sx" at line 5

This is followed by a CircuitConversionError.

CircuitConversionError: Circuit could not be converted to an internal Mitiq circuit. This may be because the circuit contains custom gates or Pragmas (pyQuil). If you think this is a bug or that this circuit should be supported, you can open an issue at https://github.com/unitaryfund/mitiq.

The circuit I have been trying to fold is given below:

'
from mitiq import zne as mz
from qiskit import *
qr = QuantumRegister(n)
qc_basis = QuantumCircuit(qr)
qc_basis.sx([0,2,4])
qc_basis.cx([0,2], [1,3])
qc_basis.cx([2,4], [1,3])
qc_basis.rz(np.pi+beta, 0)
qc_basis.rz(np.pi-beta, 2)
qc_basis.sx([0,2,4])
qc_basis.measure_all()
qc_folded = mz.scaling.fold_global(qc_basis, scale_factor=3.)
`

[github-actions]

Hello @amrit-11, thank you for your interest in Mitiq!
If this is a bug report, please provide screenshots and/or minimum viable code to reproduce your issue, so we can do our best to help get it fixed. If you have any questions in the meantime, you can also ask us on the Unitary Fund Discord.

[rmlarose]

Thanks @amrit-11 for reporting. We are aware of this issue and tracking it in #1073, so I will close this one as a duplicate.

In the meantime, you can do qiskit.transpile(qc_basis, basis_gates=["u1", "u2", "u3"]) and then you should be able to fold the circuit.