Specify control state

Required prerequisites

• Search the issue tracker to check if your feature has already been mentioned or rejected in other issues.

Describe the feature

This is how to perform controlled operations:

import cudaq

@cudaq.kernel
def x_kernel(qubit: cudaq.qubit):
    x(qubit)

@cudaq.kernel
def kernel():
    
    controls = cudaq.qvector(2)
    target = cudaq.qubit()
    
    # Default: apply the x_kernel if controls are |1> 
    cudaq.control(x_kernel, controls, target) 
    
results = cudaq.sample(kernel)
print(cudaq.draw(kernel))

Currently, when the controls = 11 the target is applied.

What if I want to specify the control state for which the target is applied?

I may want to apply the target when the controls = 01 or controls = 00

See here for similar feature in qiskit.

Start from the cudaq.control(x_kernel, controls, target) entry point shown in the issue and compare the requested behavior with Qiskit's ctrl_state reference. Define how control states such as 11, 01, and 00 should be specified, preserving the current default behavior. Done means controlled operations apply the target for the selected state and the behavior is covered by appropriate tests.