Accessing the Qsim Circuit

[PavanCyborg]

Is there any way to access the Qsim circuit after translating from the Cirq circuit to the Qsim Circuit?

I'm checking how different the Qsim circuit is concerning the Cirq Circuit. I also wanted to find out the depth of the Translated Qsim circuit.

It is provided that there are some functions under the Class QsimCircuit in qsim_circuit.py. I tried to access the translated circuit, which only returned a circuit object along with its memory address. There are no other functions available to find gate counts and the depth of the circuit.

The code which I have used to access the translated circuit:

import numpy as np
num_qubits = 5
s_int = 5
n_iterations = int(np.pi * np.sqrt(2 ** num_qubits) / 4)
qc = GroversSearch(num_qubits, s_int, n_iterations)
from qsimcirq import QSimCircuit
x = QSimCircuit(qc)
x.translate_cirq_to_qsim()

The output it returned:
Tuple Object
(<qsimcirq.qsim_avx2.Circuit at 0x732432cb9870>,
[5, 12, 33, 40, 61, 68, 89, 96, 117, 118])

[95-martin-orion]

The qsim.Circuit class provided in Python has bindings for accessing its num_qubits and gates properties:

qsim/pybind_interface/pybind_main.h

Lines 301 to 304 in 55b4d0e

	py::class_<Circuit>(m, "Circuit") \
	.def(py::init<>()) \
	.def_readwrite("num_qubits", &Circuit::num_qubits) \
	.def_readwrite("gates", &Circuit::gates); \

You should be able to retrieve these with:

qsim_circuit = x.translate_cirq_to_qsim()
print(qsim_circuit.num_qubits)  # prints number of qubits in qsim_circuit
print(len(qsim_circuit.gates))  # prints number of gates in qsim_circuit

Note that these bindings are only for CPU implementations of qsim; the GPU implementation does not have these bindings.

---

For circuit depth, you can use the output you printed above. QSimCircuit.translate_cirq_to_qsim returns:

qsim/qsimcirq/qsim_circuit.py

Lines 391 to 392 in 55b4d0e

	:return: a tuple of (C++ qsim Circuit object, moment boundary
	gate indices)

So the length of [5, 12, 33, 40, 61, 68, 89, 96, 117, 118] is the number of moments in the circuit (i.e. its depth).

[PavanCyborg]

moment boundary
gate indices

Thanks for your help. I have now received clarification regarding how to find the depth of the translated QSIM circuit. But one thing bothers me. When I used print(len(qsim_circuit.gates)), I received the following error. Do you have any suggestions for this one?!!

---

TypeError Traceback (most recent call last)
TypeError: Unregistered type : qsim::Gate<float, qsim::Cirq::GateKind>

The above exception was the direct cause of the following exception:

TypeError Traceback (most recent call last)
Cell In[16], line 4
2 print(ckt)
3 print(ckt.num_qubits)
----> 4 print(len(ckt.gates))

TypeError: Unable to convert function return value to a Python type! The signature was
(self: qsimcirq.qsim_avx2.Circuit) -> List[qsim::Gate<float, qsim::Cirq::GateKind>]

Once again, thanks for your previous response!!!

[95-martin-orion]

Ah, this appears to be an issue with the python bindings - there is no Gate binding, and apparently the python code can't operate on a list[Gate] without having a binding for Gate.

Fortunately, there is an alternate solution: the "moment boundary gate indices" list that we used to find the circuit depth earlier is a list of the number of gates before each moment boundary. Using the previous list as an example:

[5, 12, 33, 40, 61, 68, 89, 96, 117, 118]

The first moment has 5 gates, the next has 7 (12-5), and so on. The final element of this list (118) is therefore the total number of gates in the translated circuit object. In code:

# Added "moment_boundaries" to pick up the list of moment boundary gate indices
qsim_circuit, moment_boundaries = x.translate_cirq_to_qsim()
print(qsim_circuit.num_qubits)  # prints number of qubits in qsim_circuit
print(moment_boundaries[-1])  # prints number of gates in qsim_circuit