A. Stepanenko

K. Chernova

M. Mazanov

M. Gorlach

Time-optimal control of large quantum systems is computed efficiently by applying boundary conditions to a brachistochrone–Lax framework.

Finding time-optimal quantum control becomes rapidly harder as systems grow. Combining the quantum brachistochrone with Lax-pair methods, we reduce the number of unknowns from quadratic to linear in system size. Applied to excitation transfer in qubit lattices with tunable couplings, the framework yields quantum speed limits and optimal transport strategies, opening efficient control of large-scale quantum systems.

We present an approach to compute time-optimal control of a quantum system which combines quantum brachistochrone and Lax pair techniques and enables efficient investigation of large-scale quantum systems. We illustrate our method by finding the fastest way to transfer a single-particle excitation in a nearest-neighbor-coupled infinitely large qubit lattice with the fixed sum of squares of the couplings.

Efficient computation of quantum time-optimal control