Troblem in T gate counts in azureqre from a qiskit qasm file

[QC-sanjib]

I try to find resources for the circuit that I generate using Qiskit. Here I use qasm file as an input. circuit is

. In this circuit, the number of T-gates and Tdg-gates is 30 and 26, respectively. But in the Azure output, I saw the number T state is 78, and the number T gates in the input algorithm is 0. The count 78 is coming from rotation gates with an arbitrary angle. How are the results like this? I am expecting results number of T states to be 30+26.

[idavis]

Hi @QC-sanjib,

Transpilation for the default backend must be disabled, otherwise it will transpile to the Q# gate set. The API examples in the estimation-qiskit.ipynb show how this is done and I've extracted the samples below.

If you use the estimate function:

from qsharp.estimator import EstimatorParams
from qsharp.interop.qiskit import estimate

params = EstimatorParams()
result = estimate(circ, params, skip_transpilation=True)

Alternatively, if you use the ResourceEstimatorBackend to perform the estimation:

from qsharp.interop.qiskit import ResourceEstimatorBackend
from qsharp.estimator import EstimatorParams

params = EstimatorParams()
backend = ResourceEstimatorBackend(skip_transpilation=True)

job = backend.run(circ, params)
result = job.result()

You can also use the OpenQASM 3.0 estimation API if you want to use Qiskit's OpenQASM Exporter. You see usage in the estimation-openqasm.ipynb :

from qsharp.estimator import EstimatorParams
from qsharp.openqasm import estimate
from qiskit.qasm3.exporter import Exporter

circ = ... # create QuantumCircuit

# Export the circuit to QASM vis Qiskit's OpenQASM 3 exporter
program = Exporter().dumps(circ)

params = EstimatorParams()
result = estimate(program, params)

[QC-sanjib]

I appreciate the clarification. It helps a lot with my work.
Now I have another problem - suppose we have a circuit from Qiskit -

The circuit has T gate and X(pi/8) gate. With translation, Azure QRE gives 0 T gate, and the number of rotation gates with an arbitrary angle is 3. But without transpilation, Azure QRE gives 4 T gates present in the circuit because X(pi/8) is HTH, which is expected.
Now, question what steps are involved in transpilation for this small circuit that gives 0 T gate and 3 rotation gate with an arbitrary angle?
Another question, what is the Q# gate set?
If you share the transpiller step details, that also helps a lot!

[idavis]

@QC-sanjib, we call Qiskit's transpile function from the Q# backend using the default QirTarget which uses these gates. You can create your own backend like we do and pass it in QSharpBackend(target=target) and transpilation will use that target to define the intrinsic gates.

[idavis]

@QC-sanjib Closing this for now. Feel free to open another ticket if you have any issues.