Inspecting the circuit

Quantum circuits in Amazon Braket have a pseudo-time concept called Moments. Each qubit can experience a single gate per Moment. The purpose of Moments is to make circuits and their gates easier to address and to provide a temporal structure.

Note

Moments generally do not correspond to the real time at which gates are executed on a QPU.

The depth of a circuit is given by the total number of Moments in that circuit. You can view the circuit depth calling the method circuit.depth as shown in the following example.

# define a circuit with parametrized gates
circ = Circuit().rx(0, 0.15).ry(1, 0.2).cnot(0,2).zz(1, 3, 0.15).x(0)
print(circ)
print('Total circuit depth:', circ.depth)

T  : |   0    |    1     |2|

q0 : -Rx(0.15)-C----------X-
               |
q1 : -Ry(0.2)--|-ZZ(0.15)---
               | |
q2 : ----------X-|----------
                 |
q3 : ------------ZZ(0.15)---

T  : |   0    |    1     |2|
Total circuit depth: 3

The total circuit depth of the circuit above is 3 (shown as moments 0, 1, and 2). You can check the gate operation for each moment.

Moments functions as a dictionary of key-value pairs.

• The key is MomentsKey(), which contains pseudo-time and qubit information.

• The value is assigned in the type of Instructions().

moments = circ.moments
for key, value in moments.items():
    print(key)
    print(value, "\n")

MomentsKey(time=0, qubits=QubitSet([Qubit(0)]))
Instruction('operator': Rx('angle': 0.15, 'qubit_count': 1), 'target': QubitSet([Qubit(0)]))

MomentsKey(time=0, qubits=QubitSet([Qubit(1)]))
Instruction('operator': Ry('angle': 0.2, 'qubit_count': 1), 'target': QubitSet([Qubit(1)]))

MomentsKey(time=1, qubits=QubitSet([Qubit(0), Qubit(2)]))
Instruction('operator': CNot('qubit_count': 2), 'target': QubitSet([Qubit(0), Qubit(2)]))

MomentsKey(time=1, qubits=QubitSet([Qubit(1), Qubit(3)]))
Instruction('operator': ZZ('angle': 0.15, 'qubit_count': 2), 'target': QubitSet([Qubit(1), Qubit(3)]))

MomentsKey(time=2, qubits=QubitSet([Qubit(0)]))
Instruction('operator': X('qubit_count': 1), 'target': QubitSet([Qubit(0)]))

You can also add gates to a circuit through Moments.

new_circ = Circuit()
instructions = [Instruction(Gate.S(), 0),
                Instruction(Gate.CZ(), [1,0]),
                Instruction(Gate.H(), 1)
]
new_circ.moments.add(instructions)
print(new_circ)

T  : |0|1|2|

q0 : -S-Z---
        |
q1 : ---C-H-

T  : |0|1|2|