Finite-resource cooling of qudits beyond thermodynamic length

Abstract

Cooling a quantum system with $N$ thermal machines costs more than Landauer's bound. For swap-based collision models the excess is set by thermodynamic length, which is optimal for qubits and was suggested by numerics to be optimal in general. We show that for qudits, permutations of energy eigenstates that use several resonant transitions at once do better for every spectrum, reducing the excess by up to 83% near the ground state. To second order, coherent collisions do no better, and at infinite temperature $d_M$-level machines reduce the excess by at most a factor $d_M-1$.

arXiv comment5 pages, 2 figures, 1 table, plus 7 pages of Supplemental Material. Code and data: https://github.com/anshM123/Resonant-Collision-Cooling