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arXiv:1509.08094

A Quantum Paradox of Choice and Purported Classical Analogues

Emily Adlam, Adrian Kent

Published Sep 27, 2015• 1 citation
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Abstract

We recently considered the task of summoning an unknown quantum state and proved necessary and sufficient conditions for Alice to be able to guarantee to complete the task when there may be several possible calls, of which she need only respond to one. We showed that these are strictly stronger conditions than those previously established by Hayden and May for the case where Alice knows there will only be one call. We introduced the concept of a {\it quantum paradox of choice} to summarize the implications of these results: Alice is given more options to complete our version of the task, yet one can easily construct examples where our version is impossible and the apparently simpler version considered by Hayden-May is possible. Finkelstein has argued that one can identify analogous classical paradoxes of choice in a relativistic setting. We examine Finkelstein's proposed classical tasks and explain why they seem to us disanalogous.

DOI
10.48550/arxiv.1509.08094

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We recently considered the task of summoning an unknown quantum state and proved necessary and sufficient conditions for Alice to be able to guarantee to complete the task when there may be several possible calls, of which she need only respond to one. We showed that these are strictly stronger conditions than those previously established by Hayden and May for the case where Alice knows there will only be one call. We introduced the concept of a {\it quantum paradox of choice} to summarize the implications of these results: Alice is given more options to complete our version of the task, yet one can easily construct examples where our version is impossible and the apparently simpler version considered by Hayden-May is possible. Finkelstein has argued that one can identify analogous classical paradoxes of choice in a relativistic setting. We examine Finkelstein's proposed classical tasks and explain why they seem to us disanalogous.
The properties of quantum information in space-time can be investigated by studying operational tasks, such as ``summoning,'' in which an unknown quantum state is supplied at one point and a call is made at another for it to be returned at a third. Hayden and May [arXiv:1210.0913] recently proved necessary and sufficient conditions for guaranteeing successful return of a summoned state for finite sets of call and return points when there is a guarantee of at most one summons. We prove necessary and sufficient conditions when there may be several possible summonses and complying with any one constitutes success, and we demonstrate the existence of an apparent paradox: The extra freedom makes it strictly harder to complete the summoning task. This result has practical applications for distributed quantum computing and cryptography and implications for our understanding of relativistic quantum information and its localization in space-time.
If the concept of “free will” is reduced to that of “choice” all physical world share the latter quality. Anyway the “free will” can be distinguished from the “choice”: The “free will” involves implicitly certain preliminary goal, and the choice is only the mean, by which it can be achieved or not by the one who determines the goal. Thus, for example, an electron has always a choice but not free will unlike a human possessing both. Consequently, and paradoxically, the determinism of classical physics is more subjective and more anthropomorphic than the indeterminism of quantum mechanics for the former presupposes certain deterministic goal implicitly following the model of human freewill behavior.The choice is usually linked to very complicated systems such as human brain or society and even often associated with consciousness. In its background, the material world is deterministic and absolutely devoid of choice. However, quantum mechanics introduces the choice in the fundament of physical world, in the only way, in which it can exist: All exists in the “phase transition” of the present between the uncertain future and the well-ordered past. Thus the present is forced to choose in order to be able to transform the coherent state of future into the well-ordering of past. The concept of choice as if suggests that there is one who chooses. However quantum mechanics involves a generalized case of choice, which can be called “subjectless”: There is certain choice, which originates from the transition of the future into the past. Thus that kind of choice is shared of all existing and does not need any subject: It can be considered as a low of nature.There are a few theorems in quantum mechanics directly relevant to the topic: two of them are called “free will theorems” by their authors, Conway and Kochen, and according to them: “Do we really have free will, or, as a few determined folk maintain, is it all an illusion? We don’t know, but will prove in this paper that if indeed there exist any experimenters with a modicum of free will, then elementary particles must have their own share of this valuable commodity” “The import of the free will theorem is that it is not only current quantum theory, but the world itself that is non-deterministic, so that no future theory can return us to a clockwork universe”.Those theorems can be considered as a continuation of the so-called theorems about the absence of “hidden variables” in quantum mechanics.
Looking at conditional probability from the right perspective allows one to avoid classic paradoxical aspects of quantum mechanics. We discuss, as an elementary analogue of quan-tum states, a classical example (an urn of unknown composition) with similar (putative) paradoxical situ-ations, despite the fact that there is no quantum effect to which they could be ascribed. A crucial feature is that we look at them from an epis-temic point of view and not from the viewpoint of a (seemingly) ontologi-cal reality.
Since its discovery quantum teleportation has often been seen as a manifestation, indeed the epitome, of the very paradoxical and mysterious nature of quantum theory itself. It is commonly regarded as genuinely quantum and essentially paradoxical. Although a common approach to teleportation amongst physicists nowadays is a somewhat operational one, some researchers are making an effort to deflate the above views. On the one hand, it was recently argued that the paradox of information transfer taking place in teleportation is dissolved (Timpson, 2006) by appealing the very notion of information. On the other hand, it was demonstrated that some classical versions of teleportation retain its important features, which hitherto were considered genuinely quantum (Cohen, 2003; Collins&Popescu, 2002; Hardy, 1999; Mor, 2006; Spekkens, 2007). I will present a special version of a quantum teleportation protocol which is in a sense split into classical and quantum steps. This description provides us with a unified picture of teleportation in both domains. It will be explicitly shown how classical teleportation is embedded in the quantum protocol. Moreover, the classical step can be successfully accomplished even if the state shared by the parties is completely disentangled [this is consistent with the result obtained in (Wang, 2005)]. Yet, all the (apparent) paradoxical features usually associated with quantum teleportation are clearly present in this step. In particular, this demonstrates that entanglement cannot be ultimately responsible and not necessary for the (paradoxical?) information transfer. Thus, even if one considers teleportation as mysterious, all its mysteries are shifted from quantum domain into purely classical one.