Introduction

PennyLane provides a bridge between classical and quantum computations, making it easy to build and optimize hybrid computations. Prominent examples are variational quantum eigensolvers and quantum machine learning models.

Bridging the classical and quantum world

Classical computations, as well as optimization or training of models, are executed using one of the standard scientific computing or machine learning libraries. PennyLane provides an interface to these libraries, making them quantum-aware.

PennyLane’s standard interface is NumPy, but interfaces to powerful machine learning libraries like PyTorch and Tensorflow are also available.

The quantum computations are sent to a device for execution. A device can be real quantum hardware or a classical simulator. PennyLane comes with default simulator devices, but is well-integrated with external software and hardware to run quantum circuits—such as Xanadu’s Strawberry Fields, Rigetti’s Forest, IBM’s Qiskit, or Google’s Cirq.

Communication between the classical computing library and quantum devices is coordinated in PennyLane via a suite of plugins:

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The main job of PennyLane is to manage the evaluation of parametrized quantum circuits (so-called variational circuits) on quantum devices, and to make them accessible to the machine learning libraries. PennyLane also provides access to gradients of quantum circuits, which the machine learning library can use to perform backpropagation, including through quantum circuits—an essential process for optimization and machine learning.

More details

In the following sections you can learn more about the key features of PennyLane:

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  1. Quantum circuits shows how PennyLane unifies and simplifies the process of programming quantum circuits with trainable parameters.
  1. Interfaces introduces how PennyLane is used with different optimization libraries to optimize quantum circuits or hybrid computations.
  1. Quantum operations outlines the various quantum circuit building blocks provided in PennyLane.
  1. Measurements presents the different options available to measure the output of quantum circuits.
  1. Templates gives an overview of different larger-scale composable layers for building quantum algorithms.
  1. Optimizers details the built-in tools for optimizing and training quantum computing and quantum machine learning circuits.
  1. Configuration provides details about how to customize PennyLane and provide credentials for quantum hardware access.