Nonseparability and Counterfactuality

Riuji Mochizuki

In this study, we show that it is possible to explain the quantum measurement process within the framework of quantum mechanics without any additional postulates.We do not delve into a deep discussion regarding what the measurement problem actually is, and only examine the problems that seem to exist between classical and quantum physics.Relations between quantum and classical equations of motion are briefly reviewed to show that the transition from a superposition of quantum states to an eigenstate, namely, decoherence, is necessary to ensure that the expectation values in quantum mechanics obey the classical equations of motion.Several Bell-type inequalities and the Kochen-Specker theorem are also reviewed to clarify the concepts of nonseparability and counterfactual definiteness in quantum mechanics.The main objective of this study is to show that decoherence is an inherent characteristic of quantum states caused by the quantum uncertainty relation.We conclude that the quantum measurement process can indeed be explained within the framework of pure quantum mechanics.We also show that our conclusion is consistent with the counterfactual indefiniteness of quantum mechanics.

A. C. de la Torre, Pedro Jose Catuogno, Sebastián Ferrando

Bernard d’Espagnat

Lev Vaidman A

The counterfactuality of recently proposed protocols is analyzed. A definition of `counterfactuality' is offered and it is argued that an interaction-free measurement of the presence of an opaque object can be named `counterfactual', while proposed "counterfactual" measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name `counterfactual' is not appropriate for recent "counterfactual" protocols which transfer quantum states by quantum direct communication.

Lev Vaidman A

The counterfactuality of recently proposed protocols is analyzed. A definition of “counterfactuality” is offered and it is argued that an interaction-free measurement (IFM) of the presence of an opaque object can be named “counterfactual”, while proposed “counterfactual” measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name “counterfactual” is not appropriate for recent “counterfactual” protocols which transfer quantum states by quantum direct communication.

Richard Healey