Lewis-Riesenfeld invariants and transitionless tracking algorithm

TL;DR

This paper explores the relationship between Lewis-Riesenfeld invariants and the transitionless tracking algorithm, demonstrating their potential equivalence in designing shortcuts for quantum adiabatic processes.

Contribution

It reveals the strong connection and potential equivalence between two different inverse-engineering methods for quantum shortcuts, providing new insights into their relationship.

Findings

The two approaches are strongly related and potentially equivalent.

Explicit examples include expansions of harmonic traps and two-level system state preparation.

The inverse-engineering operations can be reinterpreted across both methods.

Abstract

Different methods have been recently put forward and implemented experimentally to inverse engineer the time dependent Hamiltonian of a quantum system and accelerate slow adiabatic processes via non-adiabatic shortcuts. In the "transitionless tracking algorithm" proposed by Berry, shortcut Hamiltonians are designed so that the system follows exactly, in an arbitrarily short time, the approximate adiabatic path defined by a reference Hamiltonian. A different approach is based on designing first a Lewis-Riesenfeld invariant to carry the eigenstates of a Hamiltonian from specified initial to final configurations, again in an arbitrary time, and then constructing from the invariant the transient Hamiltonian connecting these boundary configurations. We show that the two approaches, apparently quite different in form and so far in results, are in fact strongly related and potentially equivalent, so that the inverse-engineering operations in one of them can be reinterpreted and understood in terms of the concepts and operations of the other one. We study as explicit examples the expansions of time-dependent harmonic traps and state preparation of two level systems.