Highly Excited Quantum Many-Body States on Demand

We present a way to quench a quantum many-body system directly from its ground state to an asymptotically stationary excited state.  In the hard-core limit of a gas of bosons in 1D with delta function interactions, we show theoretically that a stationary excited state is immediately reached for the central Bragg peak after a Bragg pulse is applied to the system.  Specifically, its rapidity distribution (the momentum distribution of the emergent quasiparticles) does not evolve. This is counterintuitive, as one would naively expect the remaining cloud to undergo a breathing oscillation after losing a large fraction of its atoms.  We show that a similar stationary excited state can be accessed experimentally away from the hard-core limit by simultaneously changing the trap depth when the Bragg pulse is applied.  This class of stationary excited states is somewhat reminiscent of quantum many-body scar states.