## How to apply a quantum channel?

How do I use this algorithm? What does that parameter do?
Yucheng He
Posts: 4
Joined: 20 May 2022, 00:40

### How to apply a quantum channel?

I wish to apply a series of quantum channels on a specific site. For example, consider a dephasing channel, it has the form that $$\rho\rarr(1-p)I\rho+pZ\rho Z$$, which means, for a density matrix, $$\rho$$=\pmatrix{a&b\\c&d}, it will has the form \pmatrix{a&(1-2p)b\\(1-2p)c&d}.
How could this function be realized in TenPy?
Johannes
Posts: 337
Joined: 21 Jul 2018, 12:52
Location: TU Munich

### Re: How to apply a quantum channel?

I'm confused - what state do you start with? Some ground state, or other pure state, represented as an MPS? What do you want to calculate afterwards? You can use TeNPy to get the single-site reduced density matrix, and then apply the dephasing channel, but you can not apply it on the whole MPS: it's no longer a pure state afterward, so it can't be represented directly by an MPS. Are you thinking about using purification?
Yucheng He
Posts: 4
Joined: 20 May 2022, 00:40

### Re: How to apply a quantum channel?

Yeah, I am thinking about applying the dephasing channel to a single site and then considering the whole system's evolution afterward. That is, the whole system is no longer a pure state.