Order operation on multiple qubits fails to compile

[peter-campora]

When compiling a simple qasm program via pytket-qir, I hit the following error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[14], line 1
----> 1 qir_prog = pytket_to_qir(circuit, name="test_pytket_qir", qir_format=QIRFormat.BINARY)

File ~/hqcompiler-dev/lib/python3.10/site-packages/pytket/qir/conversion/api.py:65, in pytket_to_qir(circ, name, qir_format, wfh, int_type, cut_pytket_register)
     50 """converts given pytket circuit to qir
     51 
     52 :param circ: given circuit
   (...)
     59   into smaller registers, default value false
     60 """
     62 if len(circ.q_registers) > 1 or (
     63     len(circ.q_registers) == 1 and circ.q_registers[0].name != "q"
     64 ):
---> 65     raise ValueError(
     66         """The circuit that should be converted should only have the default
     67         quantum register. You can convert it using the pytket
     68         compiler pass `FlattenRelabelRegistersPass`."""
     69     )
     71 if int_type != 32 and int_type != 64:
     72     raise ValueError("the integer size must be 32 or 64")

ValueError: The circuit that should be converted should only have the default
            quantum register. You can convert it using the pytket
            compiler pass `FlattenRelabelRegistersPass`.

The relevant code to hit the error is:

from pytket.qir.conversion.api import QIRFormat, pytket_to_qir
from pytket.qasm import circuit_from_qasm_str, circuit_to_qasm_str, circuit_from_qasm_wasm
from qjobs import QPU, Batch, Program
from base64 import b64encode

qasm = """OPENQASM 2.0;
include "hqslib1_dev.inc";
qreg q[2];
qreg q1[1];
creg c[2];
creg c2[5];
creg c3[5];
creg c4[5];
c2 = 4;
c3 = 1;

order2 q[0], q1[0];
h q[0];

measure q->c;
"""
circuit = circuit_from_qasm_str(qasm)
# to verify that your qasm is the same after pytket loading, you can use the following
new_qasm_str = circuit_to_qasm_str(circuit, header="hqslib1_dev")

[cqc-melf]

The problem is, that the circuit has two quantum registers, you can solve this with using the pytket pass FlattenRelabelRegistersPass and it should work. If you think we should apply this pass by default, I am happy to discuss this.

[peter-campora]

Seems that using pytket-quantinuum or manually invoking that pass, as @cqc-melf mentioned takes care of the issue!