Use Amazon Braket Hybrid Jobs and PennyLane to run a QAOA algorithm - Amazon Braket

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Use Amazon Braket Hybrid Jobs and PennyLane to run a QAOA algorithm

In this section, you’ll use what you’ve learned to write an actual hybrid program using PennyLane with parametric compilation. You use the algorithm script to address a Quantum Approximate Optimization Algorithm (QAOA) problem. The program creates a cost function corresponding to a classical Max Cut optimization problem, specifies a parametrized quantum circuit, and uses a simple gradient descent method to optimize the parameters so that the cost function is minimized. In this example, we generate the problem graph in the algorithm script for simplicity, but for more typical use cases the best practice is to provide the problem specification through a dedicated channel in the input data configuration. The flag parametrize_differentiable defaults to True so you automatically get the benefits of improved runtime performance from parametric compilation on supported QPUs.

import os import json import time from import save_job_result from import log_metric import networkx as nx import pennylane as qml from pennylane import numpy as np from matplotlib import pyplot as plt def init_pl_device(device_arn, num_nodes, shots, max_parallel): return qml.device( "", device_arn=device_arn, wires=num_nodes, shots=shots, # Set s3_destination_folder=None to output task results to a default folder s3_destination_folder=None, parallel=True, max_parallel=max_parallel, parametrize_differentiable=True, # This flag is True by default. ) def start_here(): input_dir = os.environ["AMZN_BRAKET_INPUT_DIR"] output_dir = os.environ["AMZN_BRAKET_JOB_RESULTS_DIR"] job_name = os.environ["AMZN_BRAKET_JOB_NAME"] checkpoint_dir = os.environ["AMZN_BRAKET_CHECKPOINT_DIR"] hp_file = os.environ["AMZN_BRAKET_HP_FILE"] device_arn = os.environ["AMZN_BRAKET_DEVICE_ARN"] # Read the hyperparameters with open(hp_file, "r") as f: hyperparams = json.load(f) p = int(hyperparams["p"]) seed = int(hyperparams["seed"]) max_parallel = int(hyperparams["max_parallel"]) num_iterations = int(hyperparams["num_iterations"]) stepsize = float(hyperparams["stepsize"]) shots = int(hyperparams["shots"]) # Generate random graph num_nodes = 6 num_edges = 8 graph_seed = 1967 g = nx.gnm_random_graph(num_nodes, num_edges, seed=graph_seed) # Output figure to file positions = nx.spring_layout(g, seed=seed) nx.draw(g, with_labels=True, pos=positions, node_size=600) plt.savefig(f"{output_dir}/graph.png") # Set up the QAOA problem cost_h, mixer_h = qml.qaoa.maxcut(g) def qaoa_layer(gamma, alpha): qml.qaoa.cost_layer(gamma, cost_h) qml.qaoa.mixer_layer(alpha, mixer_h) def circuit(params, **kwargs): for i in range(num_nodes): qml.Hadamard(wires=i) qml.layer(qaoa_layer, p, params[0], params[1]) dev = init_pl_device(device_arn, num_nodes, shots, max_parallel) np.random.seed(seed) cost_function = qml.ExpvalCost(circuit, cost_h, dev, optimize=True) params = 0.01 * np.random.uniform(size=[2, p]) optimizer = qml.GradientDescentOptimizer(stepsize=stepsize) print("Optimization start") for iteration in range(num_iterations): t0 = time.time() # Evaluates the cost, then does a gradient step to new params params, cost_before = optimizer.step_and_cost(cost_function, params) # Convert cost_before to a float so it's easier to handle cost_before = float(cost_before) t1 = time.time() if iteration == 0: print("Initial cost:", cost_before) else: print(f"Cost at step {iteration}:", cost_before) # Log the current loss as a metric log_metric( metric_name="Cost", value=cost_before, iteration_number=iteration, ) print(f"Completed iteration {iteration + 1}") print(f"Time to complete iteration: {t1 - t0} seconds") final_cost = float(cost_function(params)) log_metric( metric_name="Cost", value=final_cost, iteration_number=num_iterations, ) # We're done with the hybrid job, so save the result. # This will be returned in job.result() save_job_result({"params": params.numpy().tolist(), "cost": final_cost})

Parametric compilation is supported on all superconducting, gate-based QPUs from Rigetti Computing and Oxford Quantum Circuits with the exception of pulse level programs.