A Quantum Paradox of Choice: More Freedom Makes Summoning a Quantum State Harder

TL;DR

This paper explores how increased freedom in quantum state summoning tasks complicates their success, revealing a paradox where more options make the task harder, with implications for quantum information and cryptography.

Contribution

It extends previous work by establishing necessary and sufficient conditions for quantum summoning with multiple possible calls, revealing a paradoxical increase in difficulty with more choices.

Findings

More freedom in summoning makes success strictly harder.

Established conditions for multiple-call quantum summoning.

Implications for quantum computing and cryptography.

Abstract

The properties of quantum information in space-time can be investigated by studying operational tasks. In one such task, summoning, an unknown quantum state is supplied at one point, and a call is made at another for it to be returned at a third. Hayden-May recently proved necessary and sufficient conditions for guaranteeing successful return of a summoned state for finite sets of call and return points when there is a guarantee of at most one summons. We prove necessary and sufficient conditions when there may be several possible summonses and complying with any one constitutes success. We show there is a "quantum paradox of choice" in summoning: the extra freedom in completing the task makes it strictly harder. This intriguing result has practical applications for distributed quantum computing and cryptography and also implications for our understanding of relativistic quantum information and its localization in space-time.