Can I keep composing a series of quantum circuits into a large quantum circuit?

Question

Suppose I have a series of quantum circuits, each of them has 2 qubits:

qc = QuantumCircuit(2)
qc.h(0)
qc.crz(np.pi/2,0,1)
circ_list = [...say this is a list with 10 elements, each of them has the same structure above...]

If I also have a larger quantum circuit:

qcl = QuantumCircuit(8,8)

I want to compose each of the 10 'small circuits' onto the large circuit, I think a standard method would be:

qcom = qcl.compose(circ_list[i],[2,3]) # [2,3] is a random choice

However, if I want to simultaneously compose 10 circuits, it looks like I need to repeat the argument 10 times. I'm wondering is there a simpler way I can do that? An analogy I can think of is the reduce function:

n = [4,3,2,1]
a = reduce(lambda x,y: x*y, n)

Can I do something similar to the reduce function to compose everything at once? Thanks!!

Answer 1

Sure, you can do this with reduce but your list needs to also have the information about which registers you are composing onto.

So if your circ_list was a list of tuples where the first component was the circuit object and the second component was a list indicating which registers this circuit will be composed onto like [2,3]

Then you should be able to use reduce as:

reduce(lambda x,y: x.compose(y[0],y[1]),circ_list, qcl)

See the docs on reduce for more description: https://docs.python.org/3/library/functools.html#functools.reduce