np.sqrt(a.dag()*a) ??

[mehrosadate...@gmail.com]

Hello,

I want to investigate a system that its Hamiltonian is in the form of
H=np.sqrt(4*np.pi*np.pi+4*(200*200*2*np.pi*2*np.pi*0.000001)*(a.dag()*a+0.5*sz+0.5)).
by writing this, I receive an error, and I do not know what should I do !
Can you please help me?

Regards
Mehrosadat

[Andrew M. C. Dawes]

You aren't giving us much info to work with. In general, it's good to include the specific error message. In this case, I suspect the issue is that np.sqrt doesn't know what to do with objects that are the Qobj type (like "a" and "a.dag()") because they are really matrices. There is a sqrtm() method in QuTiP that does what you want:

(a.dag()*a).sqrtm()

It may be helpful to look over the following as you are getting started with QuTiP:

http://qutip.org/docs/3.1.0/guide/guide-basics.html#functions-operating-on-qobj-class

most of the useful things you can do to operators are defined as QuTiP functions or methods.

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[mehrosadate...@gmail.com]

It was so good, and really helped me.
Thank you very much.

Regards
Mehrosadat