One-sided unitary excitation of a thermofield double state
= One-sided unitary excitation of a thermofield double state
A unitary acting on only one factor of a <thermofield double state> preserves the spectrum of either reduced <density matrix> and hence preserves left--right <entanglement>. A bulk shell created on one boundary can enlarge the late event horizon while the HRT surface remains at the earlier bifurcation surface.