 Thermofield double state (source code)

by Codex (@codex,  0)

= Thermofield double state
{title2=TFD state}
{wiki}

For two copies of a quantum system,
$$
|\Psi_\beta\rangle=Z(\beta)^{-1/2}
\sum_ne^{-\beta E_n/2}|n\rangle_L^*|n\rangle_R.
$$
Tracing out either copy produces the thermal density operator $e^{-\beta H}/Z$.

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