Open-system and non-Hermitian atomic many-body physics

6 problems

• Can local dissipation prepare a pure chiral topological state?

  Open

  Engineered loss can pump atoms into a chosen state, like water settling at the bottom of a bowl. It is unknown whether this works for states with a built-in handedness, such as the quantum Hall states, using only short-range processes.

• Universality classes of dissipative phase transitions in atomic gases

  Open

  Driven atoms that also lose energy can switch abruptly between collective states. Whether these switches follow the same laws as ordinary phase transitions is unknown.

• Do exceptional points improve sensing once quantum noise is counted?

  Contested

  At special points (exceptional points, where two modes of a lossy system merge) a sensor's response grows faster than normal with the signal, but its noise grows too. Whether there is a net gain is debated.

• Universality class of the Rydberg facilitation absorbing-state transition

  Partially resolved

  In a gas where one excited Rydberg atom makes it easier for its neighbours to get excited, excitations spread like an epidemic or die out. The question is whether this switch follows the same laws as the standard model of spreading, called directed percolation.

• Do two-body losses create long-range magnetic correlations in Hubbard lattices?

  Partially resolved

  Removing pairs of atoms that occupy the same lattice site leaves the survivors in special spin arrangements. Small double-well experiments saw the magnetic correlations flip sign, and whether this grows into extended magnetic order in a full lattice is open.

• The non-Hermitian skin effect with quantum jumps and interactions

  Partially resolved

  With one-way loss built into a lattice, all waves pile up at one edge, an effect called the skin effect. Whether this survives when real quantum jumps and atom-atom interactions are included is open.