QASM3 exporter with parameterized circuit support

What should we add?

Qiskit C++ supports building parameterized circuits, but can not run them. One reason it does not support is QASM3 exporter implemented in QuantumCircuit class
(

qiskit-cpp/src/circuit/quantumcircuit_def.hpp

Line 1542 in 91f4b5d

std::string to_qasm3(void)

)
does not support parameterized circuit.

Move to_qasm3 function to outside of QuantumCircuit class (to other source file)
implement QASM3 exporter with parameter support

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Jun Doi (@doichanj)

Jun Doi (@doichanj) Hi, I am working on this issue. Does qiskit have a C-API to iterate over the parameters of a Quantum Circuit? The only implemented C-API I found was for number of parameters.

Also as a side note some operations currently supported in parameters like a**b are not valid QASM3 operations (should be pow(a,b)). There might be more such operations, is there a doc of all supported operations on parameters by qiskit or is it just Python operations?

Also as a side note some operations currently supported in parameters like a**b are not valid QASM3 operations (should be pow(a,b)). There might be more such operations, is there a doc of all supported operations on parameters by qiskit or is it just Python operations?

If you think there is an unrelated issue, please report it as a bug with a reproduction example.

Thank you to everyone who has submitted a PR for this issue! We currently have several promising fixes under review, so please hold off on submitting new PRs until the Qiskit team posts a follow-up comment here.

We will review the existing submissions in due course. Thank you for your patience!

I reviewed all the PRs related to this issue, and I noticed we do not have C-API to get a list of parameters used in the circuit (A list of the parameters is stored on rust side, so it is not good to have duplicate list on C++ side). So I would like to propose a stab function in QuantumCircuit class to get a list of parameters and replace the implementation of the function to C-API when it will be available.

std::vector<std::string> QuantumCircuit::parameter_symbols(void);  // please implement this one

// std::vector<Parameter> QuantumCircuit::parameters(void); // this is not required currently, it is compatible to Qiskit

Then pass the list of parameter symbols to QASM3 exporter.

Also I would like to add a limitation, we do not accept the same symbols in a circuit, because we do not have C-API to identify by UUID of Parameters, for example the following should be different parameter, but we do not accept this in Qiskit C++ at this moment.

Parameter a0("a");
Parameter a1("a");

circ.ry(a0, 0);
circ.ry(a1, 1);

So please collect a list of parameter symbols using the original symbol name for a stab function. (The original symbol name will be also used in a list of parameter set for SamplerPub/EstimatorPub)

Thank you for review. I have implemented the #146 requested solution in #157.

Added QuantumCircuit::parameter_symbols() const
Updated the default QASM3 export path to use it
Added the temporary limitation that distinct Parameter objects with the same symbol name are rejected
Verified with the test suite: 100% tests passed, 0 tests failed out of 4

The implementation keeps a clean replacement point so parameter_symbols() can later be changed to use the C API once parameter-symbol enumeration is available from the Rust-side circuit data.

Hi. I would like to contribute to this issue, if it's still available.

Hi, I opened a PR for this issue here: #159

I tried to address the QASM3 exporter support for parameterized circuits. I would appreciate any guidance on whether this is going in the right direction.

Thank you.

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QASM3 exporter with parameterized circuit support #146

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QASM3 exporter with parameterized circuit support #146

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What should we add?

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1ucian0 commented on Jun 3, 2026

Mayank447 commented on Jun 4, 2026

1ucian0 commented on Jun 8, 2026

1ucian0 commented on Jun 8, 2026

doichanj commented on Jun 11, 2026

GoiBasia commented on Jun 11, 2026

shiv152-arch commented on Jun 11, 2026

spital commented on Jun 12, 2026

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