`cnot` operation is not compiled properly in MLIR mode

[1tnguyen]

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Describe the bug

When the shorthand cnot operation is used (rather than x<cudaq::ctrl>), compiling with MLIR (--enable-mlir) produces incorrect results.

Steps to reproduce the bug

#include <cudaq.h>

struct kernel {
  auto operator()() __qpu__ {
    cudaq::qvector q(2);
    h(q[1]);
    cnot(q[1], q[0]);
    mz(q);
  }
};



int main() {
  auto result = cudaq::sample(kernel{});
  result.dump();
  return 0;
}

Testing:

• Library mode:

cudaq@73471b9ad6bf:~$ nvq++ test.cpp
cudaq@73471b9ad6bf:~$ ./a.out
{ 00:514 11:486 }

• MLIR mode: (the result is not a Bell state)

cudaq@73471b9ad6bf:~$ nvq++ --enable-mlir test.cpp
cudaq@73471b9ad6bf:~$ ./a.out
{ 10:490 11:510 }

Enable verbose logging, we can see that it was treated as X gates on individual qubits rather than a CNOT

[2024-04-02 02:43:56.697] [info] [CircuitSimulator.h:969] (apply) h(1)
[2024-04-02 02:43:56.697] [info] [CircuitSimulator.h:969] (apply) x(1)
[2024-04-02 02:43:56.697] [info] [CircuitSimulator.h:969] (apply) x(0)

Expected behavior

Correct results in MLIR mode.

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• CUDA Quantum version: Latest (nightly docker image)
• Python version: 3.10
• C++ compiler: gcc-11
• Operating system: Ubuntu 22.04

Suggestions

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