Rectangular gkp

[elib20]

Context: Currently, strawberryfields only supports square lattice GKP states. The simplest more general type of GKP states are rectangular lattice GKP states (instead of peak spacing by sqrt(pi) in q quadrature, it's sqrt(alpha*sqrt(pi)). This allows for, e.g. GKP sensor states.

Description of the Change: Adds the ability to initialize rectangular GKP states to the bosonic and fock backends.

Benefits: Wider class of states to simulate.

Possible Drawbacks:

Related GitHub Issues:

[codecov]

Codecov Report

Merging #668 (0d6c810) into master (7ee0dd4) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #668   +/-   ##
=======================================
  Coverage   98.29%   98.29%           
=======================================
  Files          75       75           
  Lines        9029     9035    +6     
=======================================
+ Hits         8875     8881    +6     
  Misses        154      154           

Impacted Files	Coverage Δ
...trawberryfields/backends/bosonicbackend/backend.py	100.00% <100.00%> (ø)
strawberryfields/backends/fockbackend/backend.py	100.00% <100.00%> (ø)
strawberryfields/backends/fockbackend/circuit.py	98.41% <100.00%> (ø)
strawberryfields/backends/fockbackend/ops.py	95.26% <100.00%> (ø)
strawberryfields/ops.py	98.30% <100.00%> (ø)

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[ilan-tz]

Nicely done! Good thinking to add more flexibility in choice of GKP state for the user.