Add Bosonic backend

[Hugh-888]

1. support construct nongaussian state

cov = torch.stack([torch.eye(4)]*3)
mean = torch.tensor([[1,1,0,0],
                     [2,2,0,0],
                     [3,3,0,0]])
weight = torch.tensor([0.1, 0.4, 0.5])
state1 = dq.NonGaussianState([cov, mean, weight])
cat = dq.CatState(r=1.55, theta=0, p=1)
vac = dq.NonGaussianState(state='vac')

2. support forward for nongaussian state

cir = dq.QumodeCircuit(nmode=2, init_state='vac', cutoff=3, backend='bosonic')
cir.cat(wires=0, r=1, theta=0, p=1)
cir.gkp(wires=1, theta=0., phi=0.)
cir.s(0, 0.)
cir.s(1, 0.)
result = cir()

3. support non-gaussian state visulisation

gkp = dq.GKPState(theta=0., phi=0., amp_cutoff=0.01, epsilon=0.05)
qvec = torch.linspace(-8, 6, 100)
pvec = torch.linspace(-10, 7, 100)
test =gkp.wigner(0, qvec, pvec, plot=True)

[sansiro77]

[sansiro77]

[sansiro77]

Now we support:

cir = dq.QumodeCircuit(nmode=2, init_state='vac', backend='bosonic')
cir.cat(0)
cir.gkp(1, 1., 1.)
cir.bs([0,1])
cir()

[sansiro77]

kappa还没加

[sansiro77]

Good job!