Effective Number Theory: Counting the Identities of a Quantum State

TL;DR

This paper develops a rigorous additive framework for effective counting in quantum systems, enabling meaningful quantification of states and outcomes that accounts for their probabilistic relevance.

Contribution

It introduces the additive theory of effective number functions (ENFs), establishing a unique minimal total for consistent counting in quantum and other sciences.

Findings

Existence of a unique ENF with minimal total

ENFs provide absolute meaning to effective counts

Applicable to quantum states and broader sciences

Abstract

Quantum physics frequently involves a need to count the states, subspaces, measurement outcomes, and other elements of quantum dynamics. However, with quantum mechanics assigning probabilities to such objects, it is often desirable to work with the notion of a "total" that takes into account their varied relevance. For example, such an effective count of position states available to a lattice electron could characterize its localization properties. Similarly, the effective total of outcomes in the measurement step of a quantum computation relates to the efficiency of the quantum algorithm. Despite a broad need for effective counting, a well-founded prescription has not been formulated. Instead, the assignments that do not respect the measure-like nature of the concept, such as versions of the participation number or exponentiated entropies, are used in some areas. Here, we develop the additive theory of effective number functions (ENFs), namely functions assigning consistent totals to collections of objects endowed with probability weights. Our analysis reveals the existence of a minimal total, realized by the unique ENF, which leads to effective counting with absolute meaning. Touching upon the nature of the measure, our results may find applications not only in quantum physics, but also in other quantitative sciences.