Construct circuits in the SDK - Amazon Braket

# Construct circuits in the SDK

This section provides examples of defining a circuit, viewing available gates, extending a circuit, and viewing gates that each device supports. It also contains instructions on how to manually allocate qubits, instruct the compiler to run your circuits exactly as defined, and build noisy circuits with a noise simulator.

You can also work at the pulse level in Braket for various gates with certain QPUs. For more information, see Pulse Control on Amazon Braket.

## Gates and circuits

Quantum gates and circuits are defined in the `braket.circuits` class of the Amazon Braket Python SDK. From the SDK, you can instantiate a new circuit object by calling `Circuit()`.

Example: Define a circuit

The example starts by defining a sample circuit of four qubits (labelled `q0`, `q1`, `q2`, and `q3`) consisting of standard, single-qubit Hadamard gates and two-qubit CNOT gates. You can visualize this circuit by calling the `print` function as the following example shows.

``````# import the circuit module
from braket.circuits import Circuit

# define circuit with 4 qubits
my_circuit = Circuit().h(range(4)).cnot(control=0, target=2).cnot(control=1, target=3)
print(my_circuit)``````
``````T  : |0| 1 |

q0 : -H-C---
|
q1 : -H-|-C-
| |
q2 : -H-X-|-
|
q3 : -H---X-

T  : |0| 1 |``````

Example: Define a parameterized circuit

In this example, we define a circuit with gates that depend on free parameters. We can specify the values of these parameters to create a new circuit, or, when submitting the circuit, to run as a task on certain devices.

``````from braket.circuits import Circuit, FreeParameter

#define a FreeParameter to represent the angle of a gate
alpha = FreeParameter("alpha")

#define a circuit with three qubits
my_circuit = Circuit().h(range(3)).cnot(control=0, target=2).rx(0, alpha).rx(1, alpha)
print(my_circuit)``````

You can create a new, non-parametrized circuit from a parametrized one by supplying either a single `float` (which is the value all free parameters will take) or keyword arguments specifying each parameter’s value to the circuit as follows.

``````my_fixed_circuit = my_circuit(1.2)
my_fixed_circuit = my_circuit(alpha=1.2)``````

Note that `my_circuit` is unmodified, so you can use it to instantiate many new circuits with fixed parameter values.

Example: See all available gates

The following example shows how to look at all the available gates in Amazon Braket.

``````import string
from braket.circuits import Gate
# print all available gates in Amazon Braket
gate_set = [attr for attr in dir(Gate) if attr in string.ascii_uppercase]
print(gate_set)``````

The output from this code lists all of the gates.

``['CCNot', 'CNot', 'CPhaseShift', 'CPhaseShift00', 'CPhaseShift01', 'CPhaseShift10', 'CSwap', 'CV', 'CY', 'CZ', 'ECR', 'H', 'I', 'ISwap', 'PSwap', 'PhaseShift', 'Rx', 'Ry', 'Rz', 'S', 'Si', 'Swap', 'T', 'Ti', 'Unitary', 'V', 'Vi', 'X', 'XX', 'XY', 'Y', 'YY', 'Z', 'ZZ']``

Any of these gates can be appended to a circuit by calling the method for that type of circuit. For example, you’d call `circ.h(0)`, to add a Hadamard gate to the first qubit.

Note

Gates are appended in place, and the example that follows adds all of the gates listed in the previous example to the same circuit.

``````circ = Circuit()
# toffoli gate with q0, q1 the control qubits and q2 the target.
circ.ccnot(0, 1, 2)
# cnot gate
circ.cnot(0, 1)
# controlled-phase gate that phases the |11> state, cphaseshift(phi) = diag((1,1,1,exp(1j*phi))), where phi=0.15 in the examples below
circ.cphaseshift(0, 1, 0.15)
# controlled-phase gate that phases the |00> state, cphaseshift00(phi) = diag([exp(1j*phi),1,1,1])
circ.cphaseshift00(0, 1, 0.15)
# controlled-phase gate that phases the |01> state, cphaseshift01(phi) = diag([1,exp(1j*phi),1,1])
circ.cphaseshift01(0, 1, 0.15)
# controlled-phase gate that phases the |10> state, cphaseshift10(phi) = diag([1,1,exp(1j*phi),1])
circ.cphaseshift10(0, 1, 0.15)
# controlled swap gate
circ.cswap(0, 1, 2)
# swap gate
circ.swap(0,1)
# phaseshift(phi)= diag([1,exp(1j*phi)])
circ.phaseshift(0,0.15)
# controlled Y gate
circ.cy(0, 1)
# controlled phase gate
circ.cz(0, 1)
# Echoed cross-resonance gate applied to q0, q1
circ = Circuit().ecr(0,1)
# X rotation with angle 0.15
circ.rx(0, 0.15)
# Y rotation with angle 0.15
circ.ry(0, 0.15)
# Z rotation with angle 0.15
circ.rz(0, 0.15)
# Hadamard gates applied to q0, q1, q2
circ.h(range(3))
# identity gates applied to q0, q1, q2
circ.i([0, 1, 2])
# iswap gate, iswap = [[1,0,0,0],[0,0,1j,0],[0,1j,0,0],[0,0,0,1]]
circ.iswap(0, 1)
# pswap gate, PSWAP(phi) = [[1,0,0,0],[0,0,exp(1j*phi),0],[0,exp(1j*phi),0,0],[0,0,0,1]]
circ.pswap(0, 1, 0.15)
# X gate applied to q1, q2
circ.x([1, 2])
# Y gate applied to q1, q2
circ.y([1, 2])
# Z gate applied to q1, q2
circ.z([1, 2])
# S gate applied to q0, q1, q2
circ.s([0, 1, 2])
# conjugate transpose of S gate applied to q0, q1
circ.si([0, 1])
# T gate applied to q0, q1
circ.t([0, 1])
# conjugate transpose of T gate applied to q0, q1
circ.ti([0, 1])
# square root of not gate applied to q0, q1, q2
circ.v([0, 1, 2])
# conjugate transpose of square root of not gate applied to q0, q1, q2
circ.vi([0, 1, 2])
# exp(i(XX+YY) theta/4), where theta=0.15 in the examples below
circ.xx(0, 1, 0.15)
# exp(-iXX theta/2)
circ.xy(0, 1, 0.15)
# exp(-iYY theta/2)
circ.yy(0, 1, 0.15)
# exp(-iZZ theta/2)
circ.zz(0, 1, 0.15)``````

Apart from the pre-defined gate set, you also can apply self-defined unitary gates to the circuit. These can be single-qubit gates (as shown in the following source code) or multi-qubit gates applied to the qubits defined by the `targets` parameter.

``````import numpy as np
# apply a general unitary
my_unitary = np.array([[0, 1],[1, 0]])
circ.unitary(matrix=my_unitary, targets=)``````

Example: Extend existing circuits

You can extend existing circuits by adding instructions. An `Instruction` is a quantum directive that describes the task to perform on a quantum device. `Instruction` operators include objects of type `Gate` only.

``````# import the Gate and Instruction modules
from braket.circuits import Gate, Instruction

circ = Circuit([Instruction(Gate.H(), 4), Instruction(Gate.CNot(), [4, 5])])

instr = Instruction(Gate.CNot(), [0, 1])

# specify where the circuit is appended

# print the instructions
print(circ.instructions)
# if there are multiple instructions, you can print them in a for loop
for instr in circ.instructions:
print(instr)

# instructions can be copied
new_instr = instr.copy()
# appoint the instruction to target
new_instr = instr.copy(target=)
new_instr = instr.copy(target_mapping={0: 5})``````

Example: View the gates that each device supports

Simulators support all gates in the Braket SDK, but QPU devices support a smaller subset. You can find the supported gates of a device in the device properties.

``````# import the device module
from braket.aws import AwsDevice

device = AwsDevice("arn:aws:braket:::device/qpu/ionq/ionQdevice")

# get device name
device_name = device.name
# show supportedQuantumOperations (supported gates for a device)
device_operations = device.properties.dict()['action']['braket.ir.jaqcd.program']['supportedOperations']
print('Quantum Gates supported by {}:\n {}'.format(device_name, device_operations))``````
``````Quantum Gates supported by IonQ Device:
['x', 'y', 'z', 'rx', 'ry', 'rz', 'h', 'cnot', 's', 'si', 't', 'ti', 'v', 'vi', 'xx', 'yy', 'zz', 'swap', 'i']``````
``````device = AwsDevice("arn:aws:braket:us-west-1::device/qpu/rigetti/Aspen-M-3")

# get device name
device_name = device.name
# show supportedQuantumOperations (supported gates for a device)
device_operations = device.properties.dict()['action']['braket.ir.jaqcd.program']['supportedOperations']
print('Quantum Gates supported by {}:\n {}'.format(device.name, device_operations))``````
``````Quantum Gates supported by Aspen-M-3:
['cz', 'xy', 'ccnot', 'cnot', 'cphaseshift', 'cphaseshift00', 'cphaseshift01', 'cphaseshift10', 'cswap', 'h', 'i', 'iswap', 'phaseshift', 'pswap', 'rx', 'ry', 'rz', 's', 'si', 'swap', 't', 'ti', 'x', 'y', 'z']``````

Supported gates may need to be compiled into native gates before they can run on quantum hardware. When you submit a circuit, Amazon Braket performs this compilation automatically.

## Manual qubit allocation

When you run a quantum circuit on quantum computers from Rigetti, you can optionally use manual qubit allocation to control which qubits are used for your algorithm. The Amazon Braket Console and the Amazon Braket SDK help you to inspect the most recent calibration data of your selected quantum processing unit (QPU) device, so you can select the best qubits for your experiment.

Manual qubit allocation enables you to run circuits with greater accuracy and to investigate individual qubit properties. Researchers and advanced users optimize their circuit design based on the latest device calibration data and can obtain more accurate results.

The following example demonstrates how to allocate qubits explicitly.

``````circ = Circuit().h(0).cnot(0, 7)  # Indices of actual qubits in the QPU
my_task = device.run(circ, s3_location, shots=100, disable_qubit_rewiring=True)``````

For more information, see the Amazon Braket examples on GitHub, or more specifically, this notebook: Allocating Qubits on QPU Devices.

Note

The OQC compiler does not support setting `disable_qubit_rewiring=True`. Setting this flag to `True` yields the following error: `An error occurred (ValidationException) when calling the CreateQuantumTask operation: Device arn:aws:braket:eu-west-2::device/qpu/oqc/Lucy does not support disabled qubit rewiring`.

## Verbatim compilation

When you run a quantum circuit on quantum computers from Rigetti, IonQ, or Oxford Quantum Circuits (OQC), you can direct the compiler to run your circuits exactly as defined without any modifications. Using verbatim compilation, you can specify either that an entire circuit be preserved precisely (supported by Rigetti, IonQ, and OQC) as specified or that only specific parts of it be preserved (supported by Rigetti only). When developing algorithms for hardware benchmarking or error mitigation protocols, you need have the option to exactly specify the gates and circuit layouts that you’re running on the hardware. Verbatim compilation gives you direct control over the compilation process by turning off certain optimization steps, thereby ensuring that your circuits run exactly as designed.

Verbatim compilation is currently supported on Rigetti, IonQ, and Oxford Quantum Circuits (OQC) devices and requires the use of native gates. When using verbatim compilation, it is advisable to check the topology of the device to ensure that gates are called on connected qubits and that the circuit uses the native gates supported on the hardware. The following example shows how to programmatically access the list of native gates supported by a device.

``device.properties.paradigm.nativeGateSet``

For Rigetti, qubit rewiring must be turned off by setting `disableQubitRewiring=True` for use with verbatim compilation. If `disableQubitRewiring=False` is set when using verbatim boxes in a compilation, the quantum circuit fails validation and does not run.

If verbatim compilation is enabled for a circuit and run on a QPU that does not support it, an error is generated indicating that an unsupported operation has caused the task to fail. As more quantum hardware natively support compiler functions, this feature will be expanded to include these devices. Devices that support verbatim compilation include it as a supported operation when queried with the following code.

``````from braket.aws import AwsDevice
from braket.device_schema.device_action_properties import DeviceActionType
device = AwsDevice("arn:aws:braket:us-west-1::device/qpu/rigetti/Aspen-M-3")
device.properties.action[DeviceActionType.OPENQASM].supportedPragmas``````

There is no additional cost associated with using verbatim compilation. You continue to be charged for tasks executed on Braket QPU devices, notebook instances, and on-demand simulators based on current rates as specified on the Amazon Braket Pricing page. For more information, see the Verbatim compilation example notebook.

Note

If you are using OpenQASM to write your circuits for the OQC and IonQ devices, and you wish to map your circuit directly to the physical qubits, you need to use the `#pragma braket verbatim` as the `disableQubitRewiring` flag is completely ignored by OpenQASM.

## Noise simulation

To instantiate the local noise simulator you can change the backend as follows.

``device = LocalSimulator(backend="braket_dm")``

You can build noisy circuits in two ways:

1. Build the noisy circuit from the bottom up.

2. Take an existing, noise-free circuit and inject noise throughout.

The following example shows the approaches using a simple circuit with depolarizing noise and a custom Kraus channel.

``````# Bottom up approach
# apply depolarizing noise to qubit 0 with probability of 0.1
circ = Circuit().x(0).x(1).depolarizing(0, probability=0.1)

# create an arbitrary 2-qubit Kraus channel
E0 = scipy.stats.unitary_group.rvs(4) * np.sqrt(0.8)
E1 = scipy.stats.unitary_group.rvs(4) * np.sqrt(0.2)
K = [E0, E1]

# apply a two-qubit Kraus channel to qubits 0 and 2
circ = circ.kraus([0,2], K)``````
``````# Inject noise approach
# define phase damping noise
noise = Noise.PhaseDamping(gamma=0.1)
# the noise channel is applied to all the X gates in the circuit
circ = Circuit().x(0).y(1).cnot(0,2).x(1).z(2)
circ_noise = circ.copy()
circ_noise.apply_gate_noise(noise, target_gates = Gate.X)``````

Running a circuit is the same user experience as before, as shown in the following two examples.

Example 1

``task = device.run(circ, s3_location)``

Or

Example 2

``task = device.run(circ_noise, s3_location)``

For more examples, see the Braket introductory noise simulator example