Minimal time to cool a quantum system near absolute zero
In plain words
The third law says absolute zero cannot be reached in a finite number of steps. The open question is how fast the temperature can fall, given limited time or equipment, for the best possible refrigerator.
Precise statement
For a finite system cooled within time t by a refrigerator of bounded size and Hamiltonian norm, determine the optimal scaling of the final temperature T(t) or ground-state infidelity with t and with resource measures (energy, bath dimension, control complexity), improving the lower bound of Masanes and Oppenheim (Nature Communications 2017) and the Landauer-versus-Nernst cost analysis (Taranto et al., 2023).
What would settle it
Matching upper and lower bounds on T(t) achieved by an explicit protocol.
Status in the literature
Lower bounds on cooling time exist since 2017; tight scaling under realistic resource accounting is not established.