Piquasso

Added

- Performance increase for the `PureFockSimulator` and `TensorflowPureFockSimulator`.

Fixed

- `GaussianState.fidelity` gave incorrect results for multiple modes and it
needed to be corrected.
- During Williamson decomposition, sometimes `scipy.linalg.sqrtm` returned with
complex matrices instead of real ones which caused problems so it is manually
casted to real.
- In `TensorflowPureFockSimulator`, the gradient of the displacement gate
matrix was not applied properly to the upstream gradient, a conjugation is
added.
- Using `TensorflowPureFockSimulator`, the input of the `Interferometer` gate
was not converted to a `tensorflow.Tensor` automatically, which has been
included.

Added

- A simulator class called `TensorflowPureFockSimulator`, which uses Tensorflow
and is able to calculate gradients.

Changed

- By enabling Tensorflow support, we dropped support for customizing the
permanent, hafnian and loop hafnian calculations through `Config`.

Fixed

- `SamplingSimulator` along with `Loss` using uniform transmissivity
(transmittance) parameters and `ParticleNumberMeasurement` produced only-zero
samples instead of the expected samples.

Added

- Support for `Attenuator` in `FockSimulator` and `PureFockSimulator`.
- `LossyInterferometer` channel for `SamplingSimulator`.
- Possibility to provide the `hafnian` as a function in `piquasso.Config`.

Changed

- The occupation number order has been changed from lexicographic to
anti-lexicographic.
- The `piquasso.api.errors` module got renamed to `piquasso.api.exceptions`.
- The `Sampling` measurement class has been unified with
`ParticleNumberMeasurement`.

Fixed

- `Kerr` gate calculations were incorrect for multiple modes in `FockSimulator`
and `PureFockSimulator`.
- Calculations that were incorrect for multiple modes using `FockSimulator`
along with `Squeezing`, `Displacement` or `CubicPhase`.
- Symmetric tensorpower ordering in Fock-backend simulations.
- Handling 0 matrix elements at Clements decomposition.