Abstract
More than a century after the inception of quantum theory, the question of which traits and phenomena are fundamentally quantum remains under debate. Here we give an answer to this question for temporal processes which are probed sequentially by means of projective measurements of the same observable. Defining classical processes as those that can---in principle---be simulated by means of classical resources only, we fully characterize the set of such processes. Based on this characterization, we show that for non-Markovian processes (i.e., processes with memory), the absence of coherence does not guarantee the classicality of observed phenomena and furthermore derive an experimentally and computationally accessible measure for non-classicality in the presence of memory. We then provide a direct connection between classicality and the vanishing of quantum discord between the evolving system and its environment. Finally, we demonstrate that---in contrast to the memoryless setting---in the non-Markovian case, there exist processes that are genuinely quantum, i.e., they display non-classical statistics independent of the measurement scheme that is employed to probe them.
Highlights
Quantum coherence is considered to be one of the fundamental traits that distinguishes quantum from classical mechanics [1,2,3]
While this always holds true for processes in classical physics, as well as memoryless quantum processes, we show, by means of an explicit example, that this is not necessarily the case for quantum processes with memory; in the presence of quantum memory, there exists a fundamentally new class of processes, which we will call “genuinely quantum” processes, that lead to nonclassical statistics independent of how they are probed
Throughout this article, we define the classicality of a process based on observed multitime statistics Pnðxn; tn; Á Á Á ; x1; t1Þ for measurements at different times ft1; ...; tng
Summary
Quantum coherence is considered to be one of the fundamental traits that distinguishes quantum from classical mechanics [1,2,3]. In a similar manner to the analysis of coherences, our results will predominantly be phrased with respect to measurements in an arbitrary, but predetermined basis, i.e., with respect to a fixed observable, raising the issue of whether classicality is merely a question of perspective; in principle, for every process, there could exist a sequential measurement scheme that yields classical statistics While this always holds true for processes in classical physics, as well as memoryless quantum processes, we show, by means of an explicit example, that this is not necessarily the case for quantum processes with memory; in the presence of quantum memory, there exists a fundamentally new class of processes, which we will call “genuinely quantum” processes, that lead to nonclassical statistics independent of how they are probed.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
