Symbol g

The passage around this formula

Let the rotor interact with an environment E=$E_1$$\otimes$$\cdots$$\otimes$ $E_N$ through a channel $\mathcal U$ . For a candidate fragment F , the conditional fragment state is $\rho_F(g)=\operatorname{Tr}_{R\bar F} \!\left[\mathcal U\bigl(\rho_R(g)\otimes\rho_E\bigr)\right]$. This equation defines what the observer receives. $\bar F$ is everything except fragment F , including the remaining environment; $\mathcal U(\rho)$=U$\rho$ $U^\dagger$ in a closed unitary model. The trace is not an assertion that the discarded systems cease to exist. It says the fragment observer has no access to them.

Read this part in the article →