A reference implementation for a quantum virtual machine in Python
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README.md

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Reference QVM

The referenceqvm is the reference implementation of the QVM outlined in the arXiv:1608:03355 by Robert Smith, Spike Curtis, and Will Zeng. It is a research package that supports rapid prototyping and development of quantum programs using pyQuil.

Currently, this QVM supports a subset of functionality in the Quil specifications, excepting certain functions (DEFCIRCUIT, WAIT, NOP).

Noise models (dephasing, Kraus operators), parametrization with bits in classical memory, and other features will be added in future releases.

Installation

You can install reference-qvm directly from the Python package manager pip using:

pip install referenceqvm

To instead install reference-qvm from source, clone this repository, cd into it, and run:

pip install -r requirements.txt -e .

This will install the reference-qvm's dependencies if you do not already have them.

Development and Testing

We use tox and pytest for testing. Tests can be executed from the top-level directory by simply running:

tox

The setup is currently testing Python 2.7 and Python 3.6.

Building the Docs

We use sphinx to build the documentation. To do this, navigate into pyQuil's top-level directory and run:

sphinx-build -b html ./docs/source ./docs/build

To view the docs navigate to the newly-created docs/build directory and open the index.html file in a browser. Note that we use the Read the Docs theme for our documentation, so this may need to be installed using pip install sphinx_rtd_theme.

Interaction with the referenceqvm

The qvm can be accessed in a similar way to the Forest QVM access. Start by importing the synchronous connection object from the referenceqvm.api module

from referenceqvm.api import QVMConnection

and initialize a connection to the reference-qvm

qvm = QVMConnection()

By default, the Connection object uses the wavefunction transition type.

Then call the qvm.wavefunction(prog) method to get back the classical memory and the pyquil.Wavefunction object given a pyquil.quil.Program object prog.

The reference-qvm has the same functionality as Forest QVM and is useful for testing small quantum programs on a local machine. For example, the same code (up to the referenceqvm.api import) can be used to simulate pyquil programs.

>>> import pyquil.quil as pq
>>> import referenceqvm.api as api
>>> from pyquil.gates import *
>>> qvm = api.QVMConnection()
>>> p = pq.Program(H(0), CNOT(0,1))
<pyquil.pyquil.Program object at 0x101ebfb50>
>>> qvm.wavefunction(p)[0]
[(0.7071067811865475+0j), 0j, 0j, (0.7071067811865475+0j)]

QVMConnection can also initialize a QVM that does not return a wavefunction but instead a unitary corresponding to the pyquil program. This can be extremely useful in terms of debugging and understanding gate physics. For example, we can examine the unitary for a CNOT operator.

>>> import pyquil.quil as pq
>>> import referenceqvm.api as api
>>> from pyquil.gates import CNOT
>>> qvm = api.QVMConnection(type_trans='unitary')
>>> p = pq.Program(CNOT(1, 0))
>>> u = qvm.unitary(p)
>>> print(u)
[[ 1.+0.j  0.+0.j  0.+0.j  0.+0.j]
 [ 0.+0.j  1.+0.j  0.+0.j  0.+0.j]
 [ 0.+0.j  0.+0.j  0.+0.j  1.+0.j]
 [ 0.+0.j  0.+0.j  1.+0.j  0.+0.j]]

How to cite the reference-qvm

If you use the reference-qvm please cite the repository as follows:

bibTex:

@misc{rqvm2017.0.0.1,
  author = {Rigetti Computing",
  title = {Reference-QVM},
  year = {2017},
  publisher = {GitHub},
  journal = {GitHub repository},
  howpublished = {\url{https://github.com/rigetticomputing},
  commit = {the commit you used}
}

and the paper outlining the Mathematical specification of the quantum-abstract-machine:

bibTeX:

@misc{1608.03355,
  title={A Practical Quantum Instruction Set Architecture},
  author={Smith, Robert S and Curtis, Michael J and Zeng, William J},
  journal={arXiv preprint arXiv:1608.03355},
  year={2016}
}