Second-order correlation function for negative delay values

[Bijita Sarma]

Dear All,

I want to plot the second-order correlation function, g^{(2)}(\tau) for a cavity-QED system. I am using the function correlation_3op_1t for this, eg. as given here:
http://qutip.org/docs/3.1.0/guide/guide-correlation.html
I want to generate the plot for negative delay values also, i.e. from -\tau to \tau. But it shows the error message "taulist must be positive and contain the element 0."
Is there any way of doing this?

Thanks a lot! 

Best regards,

Bijita Sarma

[Kevin Fischer]

Hi Bijita,

The quantum regression theorem can only be used to calculate correlators with a specific type of time ordering (see Gardiner and Zoller quantum noise), which I believe is due to the inability to evolve the master equation in reverse. Unlike the Schrodinger equation, the master equation is not reversible due to a loss of information to the environment. However, in the steady-state, you can still calculate the negative time correlator you want by switching the operators between the two times and calculating a positive correlation.

I suppose it would make sense to change the function so it just does this when called, but one needs to be more careful when it's not the steady-state correlation.

Regards,

Kevin

[Bijita Sarma]

Thanks Kevin, it was very helpful.

Regards,
Bijita