Charge quantization and detector resolution

TL;DR

This paper demonstrates that charge quantization in quantum circuits depends on detector resolution, with geometric signatures revealing whether charge appears discrete or continuous, impacting the understanding of circuit dynamics.

Contribution

It reconciles conflicting views on charge quantization by linking it to detector resolution and identifies geometric signatures in supercurrent correlations as probes.

Findings

Charge quantization depends on detector spatial resolution.

Geometric signatures in supercurrent correlations reveal charge discreteness.

Josephson junction arrays show apparent continuous charge transport.

Abstract

Charge quantization, or the absence thereof, is a central theme in quantum circuit theory, with dramatic consequences for the predicted circuit dynamics. Very recently, the question of whether or not charge should actually be described as quantized has enjoyed renewed widespread interest, with however seemingly contradictory propositions. Here, we intend to reconcile these different approaches, by arguing that ultimately, charge quantization is not an intrinsic system property, but instead depends on the spatial resolution of the charge detector. We show that the latter can be directly probed by unique geometric signatures in the correlations of the supercurrent. We illustrate these findings at the example Josephson junction arrays in the superinductor regime, where the transported charge appears to be continuous. Finally, we comment on potential consequences of charge quantization beyond superconducting circuits.