A reference implementation of Aaronson et al's CHP simulator for efficiently simulating quantum stabilizer circuits.

## Python CHP Stabilizer Simulator

A simple reference python implementation of Scott Aaronson and Daniel Gottesman’s CHP simulator as defined in their 2004 paper “Improved Simulation of Stabilizer Circuits”. This simulator is capable of simulating quantum stabilizer circuits in polynomial time and space. Specifically, it uses O(q^2*m + q*c) time and O(q^2) space where q is the number of qubits, m is the number of measurements, and c is the number of Hadamard/CNOT/Phase gates.

## Installation

The chp_sim package is available on pypi and can be installed using pip:

```python -m pip install chp_sim
```

Alternatively, you can just copy paste the chp_sim directory of the github repository into your project. The only runtime dependency is numpy.

## Usage

Here is an example of simulating a circuit:

```import chp_sim
sim = chp_sim.ChpSimulator(num_qubits=3)

# Desired circuit:
# 0: -------X-------S---H---M---
#           |
# 1: -------|---X---S---H---M---
#           |   |
# 2: ---H---@---@-------H---M---

sim.cnot(2, 0)
sim.cnot(2, 1)
sim.phase(0)
sim.phase(1)

# Show internal simulator state.
print(sim, '\n')
# prints:
#   -Y..
#   -.Y.
#   +..X
#   ----
#   +X.X
#   +.XX
#   +YYZ

# Perform measurements
v0 = sim.measure(0)
v1 = sim.measure(1)
v2 = sim.measure(2)
print(v0)
print(v1)
print(v2)
# prints [note: one of four possible results for this circuit]:
#   True (random)
#   False (random)
#   False (determined)

# Check pattern the outputs should satisfy.
assert not v0.determined
assert not v1.determined
assert v2.determined
assert bool(v0) ^ bool(v1) ^ bool(v2)
```

## Packaging

(Notes to self on how to release a new version.)

1. Edit the source code as needed and run tests.

```pytest
```
2. Build the wheel.

```python3 setup.py -q bdist_wheel
ls dist
```

```twine upload dist/*.whl --repository-url=https://test.pypi.org/legacy/ --username="\${TEST_TWINE_USERNAME}" --password="\${TEST_TWINE_PASSWORD}"
```
4. Verify the test package works.

```mkvirtualenv test --python=/usr/bin/python3
pip install numpy
pip install chp_sim --index-url=https://test.pypi.org/simple/
python -c "import chp_sim; print(chp_sim.__version__); print(chp_sim.ChpSimulator(4))"
```

```twine upload dist/*.whl --username="\${PROD_TWINE_USERNAME}" --password="\${PROD_TWINE_PASSWORD}"
```
6. Verify the prod package works.

```mkvirtualenv test --python=/usr/bin/python3
pip install chp_sim
python -c "import chp_sim; print(chp_sim.__version__); print(chp_sim.ChpSimulator(4))"
```

## Project details

This version 0.1.1

Uploaded `py3`