Information gain and measurement disturbance for quantum agents

TL;DR

This paper extends quantum measurement formalism to include quantum agents that can store quantum information, demonstrating that such agents can learn more about a system at the cost of increased disturbance, with experimental validation.

Contribution

It introduces a generalized measurement framework for quantum agents capable of storing quantum states, highlighting the tradeoff between information gain and disturbance, supported by experimental results.

Findings

Quantum agents can acquire more information than classical measurements.

Increased information gain leads to higher measurement disturbance.

Experimental system validates the theoretical tradeoff between information and disturbance.

Abstract

The traditional formalism of quantum measurement (hereafter ``TQM'') describes processes where some properties of quantum states are extracted and stored as classical information. While TQM is a natural and appropriate description of how humans interact with quantum systems, it is silent on the question of how a more general, quantum, agent would do so. How do we describe the observation of a system by an observer with the ability to store not only classical information but quantum states in its memory? In this paper, we extend the idea of measurement to a more general class of sensors for quantum agents which interact with a system in such a way that the agent's memory stores information (classical or quantum) about the system under study. For appropriate sensory interactions, the quantum agent may ``learn'' more about the system than would be possible under any set of classical measurements -- but as we show, this comes at the cost of additional measurement disturbance. We experimentally demonstrate such a system and characterize the tradeoffs, which can be done by considering the information required to erase the effects of a measurement.