Time evolution of spread complexity and statistics of work done in quantum quenches

TL;DR

This paper links the probability distribution of work done in quantum quenches to Lanczos coefficients, providing a thermodynamic perspective on spread complexity and demonstrating this connection through harmonic chain and free bosonic field theory examples.

Contribution

It establishes a novel relation between Lanczos coefficients and measurable thermodynamic quantities in quantum quenches, enabling interpretation of spread complexity.

Findings

Lanczos coefficients relate to work distribution cumulants.

Spread complexity evolution can be derived from thermodynamic quantities.

Examples show the practical computation of spread complexity after quenches.

Abstract

We relate the probability distribution of the work done on a statistical system under a sudden quench to the Lanczos coefficients corresponding to evolution under the post-quench Hamiltonian. Using the general relation between the moments and the cumulants of the probability distribution, we show that the Lanczos coefficients can be identified with physical quantities associated with the distribution, e.g., the average work done on the system, its variance, as well as the higher order cumulants. In a sense this gives an interpretation of the Lanczos coefficients in terms of experimentally measurable quantities. Consequently, our approach provides a way towards understanding spread complexity, a quantity that measures the spread of an initial state with time in the Krylov basis generated by the post quench Hamiltonian, from a thermodynamical perspective. We illustrate these relations with two examples. The first one involves quench done on a harmonic chain with periodic boundary conditions and with nearest neighbour interactions. As a second example, we consider mass quench in a free bosonic field theory in $d$ spatial dimensions in the limit of large system size. In both cases, we find out the time evolution of the spread complexity after the quench, and relate the Lanczos coefficients with the cumulants of the distribution of the work done on the system.