Quantum information: How much information in a state vector?

TL;DR

This paper explores the unique properties of quantum information stored in nonorthogonal states, highlighting fundamental limits on measurement, copying, and predictability that distinguish quantum from classical information.

Contribution

It clarifies the fundamental limits of quantum information processing related to nonorthogonal states, emphasizing their implications for quantum measurement and cloning.

Findings

Nonorthogonal quantum states cannot be distinguished reliably.

Quantum states cannot be perfectly copied or cloned.

Quantum information exhibits properties fundamentally different from classical information.

Abstract

Quantum information refers to the distinctive information-processing properties of quantum systems, which arise when information is stored in or retrieved from nonorthogonal quantum states. More information is required to prepare an ensemble of nonorthogonal quantum states than can be recovered from the ensemble by measurements. Nonorthogonal quantum states cannot be distinguished reliably, cannot be copied or cloned, and do not lead to exact predictions for the results of measurements. These properties contrast sharply with those of information stored in the microstates of a classical system.