Multi-mode creation and annihilation operators

[Niccolò Laurora]

Hi everybody,

I am a new user of Qutip, hence my question might be trivial.
I need to define a creation and destruction operators for two different modes.

I have tried the usual functions "create" and "destroy":

a = create(10)
adag = destroy(10)

b = create(10)
bdag = destroy(10)

However, if I calculate the commutator with:

commutator(a, bdag, kind="normal") 

instead of getting 0 I get the identity. 

Can anyone help me? 

Thanks!

[Éric Giguère]

The functions `create` and `destroy` create a matrix representation of the operator.

Calling the function multiple time result in the same operator, `a == b`, not operators for different modes.

You can use the `tensor` function to couple multiple systems:

a = tensor([create(N), qeye(M)])

adag = a.dag()

b = tensor([qeye(N), create(M)])

bdag = b.dag()

With this `a` apply on the first mode and `b` on the second.

(M and N does not need to be the same.)

(You can couple as many modes as needed.)

Hope this help

[Niccolò Laurora]

Thank you very much!!