"RuntimeError: Disconnected architecture graph" for some IBMQ backends

[chris-n-self]

I am getting this error when trying to compile some circuits with some IBM backends, this code fails for me:

from pytket.extensions.qiskit import qiskit_to_tk, tk_to_qiskit, IBMQBackend
from pytket.qasm import circuit_from_qasm_str

pytket_backend = IBMQBackend('ibmq_16_melbourne',
                             hub='ibm-q',
                             group='open',
                             project='main',)
pytket_circuit = circuit_from_qasm_str(
    'OPENQASM 2.0;\ninclude "qelib1.inc";\nqreg q[5];\ncreg c[5];\nu3(pi/2,0,pi) q[0];\nu3(pi/2,0,pi)'
    + ' q[1];\ncx q[1],q[0];\nu3(0,0,-pi/4) q[0];\nu3(pi/2,0,pi) q[2];\ncx q[2],q[0];\ncx q[1],q[0];\n'
    + 'u3(0,0,-pi/4) q[0];\nu3(pi/2,0,pi) q[3];\ncx q[3],q[0];\ncx q[1],q[0];\ncx q[2],q[0];\n'
    + 'cx q[1],q[0];\nu3(pi/2,0,pi) q[4];\ncx q[4],q[0];\ncx q[1],q[0];\ncx q[2],q[0];\ncx q[1],q[0];\n'
    + 'cx q[3],q[0];\nu3(0,0,pi/4) q[0];\ncx q[1],q[0];\ncx q[2],q[0];\nu3(0,0,pi/4) q[0];\ncx q[1],q[0];\n'
    + 'cx q[2],q[1];\nu3(0,0,-pi/4) q[1];\ncx q[3],q[1];\ncx q[2],q[1];\ncx q[4],q[0];\ncx q[4],q[1];\n'
    + 'cx q[2],q[1];\ncx q[3],q[1];\nu3(0,0,pi/4) q[1];\ncx q[2],q[1];\ncx q[3],q[2];\nu3(0,0,-pi/4) q[2];\n'
    + 'cx q[4],q[1];\ncx q[4],q[2];\nu3(0,0,pi/4) q[2];\ncx q[3],q[2];\ncx q[4],q[2];\ncx q[4],q[3];\n'
    + 'cx q[4],q[3];\nu3(pi/2,0,pi) q[4];\nbarrier q[0],q[1],q[2],q[3],q[4];\nbarrier q[0];\nbarrier q[1];\n'
    + 'barrier q[2];\nbarrier q[3];\nbarrier q[4];\nmeasure q[0] -> c[0];\nmeasure q[1] -> c[1];\n'
    + 'measure q[2] -> c[2];\nmeasure q[3] -> c[3];\nmeasure q[4] -> c[4];\n'
)
pytket_backend.compile_circuit(pytket_circuit, optimisation_level=2)
tk_to_qiskit(pytket_circuit).draw()

giving an error:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-6-8590b7c732c1> in <module>
     19     + 'measure q[2] -> c[2];\nmeasure q[3] -> c[3];\nmeasure q[4] -> c[4];\n'
     20 )
---> 21 pytket_backend.compile_circuit(pytket_circuit, optimisation_level=2)
     22 tk_to_qiskit(pytket_circuit).draw()

/opt/anaconda3/envs/qiskit0.25.2/lib/python3.8/site-packages/pytket/backends/backend.py in compile_circuit(self, circuit, optimisation_level)
    141         :type optimisation_level: int, optional
    142         """
--> 143         self.default_compilation_pass(optimisation_level).apply(circuit)
    144 
    145     @property

RuntimeError: Disconnected architecture graph

Whereas if I try and run the same with ibmq_santiago rather than ibmq_16_melbourne it will work fine.

I have pytket v0.9.0 and pytket-qiskit v0.9.1 installed through pip.

[cqc-alec]

Thank you for the report. This is indeed a bug in pytket 0.9.0. The relevant code has since undergone some refactoring which appears to have fixed the issue (so it should be fixed in the upcoming release, hopefully later this week).

[chris-n-self]

Great, thank you! I will look out for the new version

[chris-n-self]

I have upgraded to 0.10.0 and this now works for me so I am closing the issue.