Compact sub-circuit representation

PennyLane Help
1

Is it possible to encapsulate a multi-qubit operator (not necessary a unitary, see below) as a new gate, so when I print circuit with qmp.draw() I’d see just big box with incoming & outgoing wires and some title, but no details? Below is an example of a 6-qubit circuit w/ feed forward measurement.
If I add more qubits or concatenate several such circuits it is very hard to see the overall logic.
And displaying circuit is a very good method of debugging. Here is a minimal exmple:

import pennylane as qml
from pennylane import numpy as np
num_qubit=6 ; shots=1000
dev = qml.device('default.qubit', wires=num_qubit,shots=shots)

@qml.qnode(dev)
def f3(X):
    ninp=X.shape[0]
    ang=np.arccos(X)
    qout=ninp
    mL=[None for i in range(ninp)]
    #.... set and measure input qubits
    for i in range(ninp):  
        qml.RX(ang[i],i)
        mL[i]=qml.measure(i)   
    hw=sum(mL)   #... compute hamming weights
    qml.cond(hw == 1, qml.PauliX)(qout)  # select 1 value of HW
    return qml.probs(ninp)
nSamp=50
X=np.random.uniform(-0.99,0.99,size=(num_qubit-1,nSamp))
print(qml.draw(f3)(X[:,0]))

and the output

0: ──RX(2.00)──┤↗├────────────────────────────────────────────────────────────────┤       
1: ─────────────║───RX(0.75)──┤↗├─────────────────────────────────────────────────┤       
2: ─────────────║──────────────║───RX(2.46)──┤↗├──────────────────────────────────┤       
3: ─────────────║──────────────║──────────────║───RX(0.54)──┤↗├───────────────────┤       
4: ─────────────║──────────────║──────────────║──────────────║───RX(1.84)──┤↗├────┤       
5: ─────────────║──────────────║──────────────║──────────────║──────────────║───X─┤  Probs
                ╚══════════════║══════════════║══════════════║══════════════║═══╣         
                               ╚══════════════║══════════════║══════════════║═══╣         
                                              ╚══════════════║══════════════║═══╣         
                                                             ╚══════════════║═══╣         
                                                                            ╚═══╝

I’d like to see just a box with 6 wires of length ~5 character, no classical (black) wires.
Is there a trick to do this in PennyLane?

2

Hey @Jan_Balewski,

Good question! The answer is yes, but I think the way to do it isn’t as “nice” as you’d think. I’ll double check internally here, but you’ll probably have to create your own operator and create a custom label. I’ll get back to you!