Spikes in quantum trajectories

TL;DR

This paper investigates the subtle, scale-invariant fluctuations called spikes that occur during quantum jumps in continuously monitored quantum systems, revealing their distribution and discussing their physical significance.

Contribution

It introduces a classical analogy and computes the exact spike distribution for a monitored qubit, highlighting a previously overlooked aspect of quantum measurement dynamics.

Findings

Identifies scale-invariant spike fluctuations in quantum trajectories

Provides exact distribution of spikes for a monitored qubit

Discusses the physical and operational relevance of these fluctuations

Abstract

A quantum system subjected to a strong continuous monitoring undergoes quantum jumps. This very well known fact hides a neglected subtlety: sharp scale-invariant fluctuations invariably decorate the jump process even in the limit where the measurement rate is very large. This article is devoted to the quantitative study of these remaining fluctuations, which we call spikes, and to a discussion of their physical status. We start by introducing a classical model where the origin of these fluctuations is more intuitive and then jump to the quantum realm where their existence is less intuitive. We compute the exact distribution of the spikes for a continuously monitored qubit. We conclude by discussing their physical and operational relevance.