Recognizing how some states are built, from mixed states to singlets

TL;DR

This paper demonstrates that certain experiments can distinguish between different preparations of the same mixed quantum state, challenging the common belief that such distinctions are impossible with measurement alone.

Contribution

It introduces experimental methods to differentiate mixed state preparations, providing new insights into quantum state distinguishability.

Findings

Some experiments can distinguish mixed state preparations

Challenges the belief that mixed states are indistinguishable by measurement

Implications for quantum cryptography protocols

Abstract

It is well known that different preparations of a mixed state cannot be distinguished by a measurement of that state. Yet we show that some other experiments let us make this distinction despite a very general belief that this would not be possible. Issues in quantum cryptography that prompted this work are only briefly mentioned in this letter.