Quantum many-body scars and Hilbert-space fragmentation

4 problems

• Why the Rydberg-blockade chain shows persistent revivals

  Open

  In chains of Rydberg atoms where neighbours cannot both be excited, one special initial pattern keeps returning to itself instead of thermalizing. The underlying reason is not fully understood.

• Do PXP scar eigenstates survive as the chain becomes infinite

  Open

  The special non-thermal states have been seen only in chains of a few dozen atoms. It is unknown whether they remain special in an infinitely long chain.

• Lifetime of exact scar states under generic weak perturbations

  Partially resolved

  Some models have exactly known non-thermal states, but any realistic small disturbance should eventually destroy them. The question is how long they survive as the disturbance gets weaker.

• Relaxation time of a strongly tilted Fermi-Hubbard chain

  Open

  Atoms in a strongly tilted lattice can move only in ways that keep their centre of mass fixed, which splits their states into disconnected sectors. Weak extra processes slowly connect the sectors, and how slowly is not known.