This paper is the first step in an investigation of whether microscopic events can be reduced to a mereological composition of elementary events, especially in biological systems. The hypothesis is made that, between events in which quanta are exchanged, there is causal flow, but strictly speaking no events take place. A causal event is characterized by the possibility of an intervention or manipulation. Thus, three types of quantum mechanical events may be found: (1) detection of a quantum of energy; (2) confinement by an apparatus in a Glauber coherent state; (3) null result measurement (without exchange of quanta). The paper explores these three types of elementary causal events, e sets forth as the next step the investigation of the causal events involved in the action of a molecular motor.
This paper is the first step in an investigation of whether microscopic events can be reduced to a mereological composition of elementary events, especially in biological systems. The hypothesis is made that, between events in which quanta are exchanged, there is causal flow, but strictly speaking no events take place. A causal event is characterized by the possibility of an intervention or manipulation. Thus, three types of quantum mechanical events may be found: (1) detection of a quantum of energy; (2) confinement by an apparatus in a Glauber coherent state; (3) null result measurement (without exchange of quanta). The paper explores these three types of elementary causal events, e sets forth as the next step the investigation of the causal events involved in the action of a molecular motor.
Summary form only given. A causal order describes the order in which events occur, and how these different events can effect each other. Recently, a description of quantum mechanics making no assumption about the order of events was developed [1]. In this formalism, events are treated in terms of the ability to exchange information between each other. Applying this new formalism to quantum mechanics has shown that processes without a defined causal order can exist. Information can nonetheless be transferred through these processes. Extraordinarily, these processes can accomplish tasks which are not otherwise possible [2-4]. In our group, we have been studying methods to create and characterize one such process: the “quantum SWITCH” [5, 6]. We have shown that, using this process, one can obtain computational advantages [5]. We have also performed a specific sequence of measurements, which we used to determine just how “non-causal” our constructed process is [6].
Identifying causal relations plays an indispensable role in science, economics, medicine and everyday life. Interventionist causation associates the discovery of such relations with the possibility of manipulation or intervention. A causes B, if manipulating A in the right way can bring about changes in B. The main technical tool, the causal model, can be seen as a device for telling us how and why certain actions are more effective than others. Such models have found application in almost every scientific discipline. However, despite several decades of sophisticated analysis and a wealth of technical results, interventionist causal methods are known to fail in the quantum case. The quantum domain, with its peculiar, counterintuitive features, is widely considered an inhospitable environment in which to apply our usual causal discovery tools. This causal skepticism presents us with a puzzle. Physicists are now able to manipulate and control quantum systems, and the design and construction of quantum technology relies on an ability to identify when one strategy will work and another will fail. From the perspective of interventionist causation, it seems that a formal account of quantum causal modelling ought to be possible. The main contribution of this thesis is to provide an extension of interventionist methodology to the quantum case. In Chapter 1, I introduce interventionist causation from the perspective of two giants of the field: Judea Pearl and James Woodward. The Causal Markov Condition (CMC) and Faithfulness assumptions are presented, and I draw particular attention to the discovery of casual structure. I touch on some of the well-known problems with interventionist causation per se. In Chapter 2, I put this methodology to work in a quantum mechanical context. Following tradition, we examine one of the Bell experiments in order to determine how the classical interventionist framework fails. Noting that the usual response is to demand that one drops either the CMC or Faithfulness, I suggest that neither approach is particularly satisfactory and argue for an alternative. I discuss some reasons why the interventionist is forced to pursue this different path. In Chapter 3, I motivate the possibility of an interventionist account of quantum causation. I first look at how physicists represent quantum technology in order to make interventionist and counterfactual inferences: via the use of quantum circuit diagrams. Using three examples I demonstrate the manner in which these diagrams can be used to facilitate causal inference. In Chapter 4, I examine some recent attempts at characterising quantum causal models due to work from the quantum foundations community. I present three such accounts and explain why I endorse a fourth, the focus of the next chapter. In Chapter 5, I present a new framework that allows for the discovery of interventionist quantum causal structure. I finish the thesis with a summary and some suggestions for further work.
Quantum information technology is one of the fastest growing sectors within information technology. This paper is a conjecture about expected boundary conditions of nonlocal effects and shows the consequences of definite or indefinite causal order of entangled quantum events leading to causality. It focuses on nonlocal causality in relativistic systems, and introduces the notion of quantum causal coherence as a nonlocal property of relativistic causality, reflecting the relation of entanglement and the principle of least action. It is shown, that the principle of least action is the self-consistency mechanism of nonlocal causality in relativistic scenarios, especially in timelike scenarios of entangled quanta. From the view of relativistic scenarios, this paper examines the possibility of causal loops in quantum causal relations and investigates quantum causal relations in well established experiments.
Indétermination causale et dynamicité en mécanique quantique La mécanique quantique permet la superposition des processus, entraînant une véritable absence de structure causale classique. Cette thèse étudie l'indétermination causale via le formalisme des matrices de processus, modélisant des processus où différentes parties respectent localement les lois quantiques sans supposer une structure causale globale bien définie, ce qui conduit à un ordre causal indéfini. Un exemple est le "quantum switch" (QS), où les opérations de deux parties A et B sont appliquées en superposition quantique des deux ordres causaux possibles. L'objectif principal de ce travail est de mieux comprendre les processus avec ordre causal indéfini ayant une interprétation physique claire, tant pratiquement, en explorant comment les réaliser et quels avantages en traitement de l'information ils offrent, que fondamentalement, en découvrant de nouvelles propriétés des processus avec trois parties ou plus.Nous commençons par rappeler que certaines implémentations expérimentales du QS ont été contestées car les opérations A et B étaient utilisées plusieurs fois, simulant ainsi un ordre causal indéfini plutôt que le réalisant vraiment. Bien que les deux processus soient indiscernables dans un régime d'énergie infinie, limiter l'énergie disponible introduit des imperfections permettant de distinguer les processus utilisant un nombre différent d'opérations. En comparant le QS à une de ses simulations naturelles dans un scénario contraint en énergie, nous trouvons que le QS est plus performant pour réaliser une tâche donnée, ce qui soulève de nouvelles questions sur les avantages énergétiques potentiels de l'indétermination causale.Nous abordons ensuite la métrologie quantique et affirmons que certaines revendications attribuant des avantages au QS par rapport à des processus à ordres causaux définis ne tiennent pas si une comparaison plus équitable est faite. En examinant les ''quantum circuits with quantum control"(QC-QC), nous trouvons divers exemples où des processus à ordre causal indéfini peuvent offrir (ou non) un avantage. Malgré l'avantage observé des QC-QC sur des circuits quantiques avec superposition causale, nous soulignons que des recherches supplémentaires sont nécessaires pour affirmer que l'ordre causal dynamique, caractéristique des QC-QC, est une ressource valable en métrologie quantique.Motivés par cette observation, nous formalisons la notion d'ordre causal dynamique, qui consiste en un ordre causal établi en cours de route plutôt que fixé a priori. Nous identifions une nouvelle manière pour l'ordre causal d'être dynamique : avec au moins quatre parties, il peut y avoir un ordre dynamique non influençable par le choix des parties passées. Cela nous conduit à introduire la notion d'ordre causal dynamique mais non influençable, pour les corrélations causales et les processus dans le formalisme des QC-QC. Cela permet de formaliser comment certains processus quantiques peuvent avoir des ordres causaux à la fois indéfinis et dynamiques, et de montrer que l'avantage des QC-QC en métrologie quantique ne peut être attribué à cette caractéristique.Enfin, nous réfléchissons à l'impact de la recherche scientifique sur la société. Après avoir analysé les implications politiques de la recherche scientifique, nous nous concentrons sur les technologies quantiques. Nous montrons qu'au-delà de quelques particularités quantiques, les enjeux éthiques associés aux technologies quantiques sont en fait plus généraux et déjà connus. Nous observons que, plus généralement, c'est le fonctionnement global de la recherche scientifique qui pourrait nécessiter une remise en question, notamment vis-à-vis des enjeux sociaux et environnementaux, ce qui nous pousse à proposer de nouvelles façons de pratiquer la recherche scientifique.
Quantum information technology is one of the fastest crowing sectors within information technology. This paper is a conjecture about expected boundary conditions of nonlocal effects and shows the consequences of definite or indefinite causal order of entangled quantum events leading to causality. It focuses on nonlocal causality in relativistic systems, and introduces the notion of quantum causal coherence as a nonlocal property of relativistic causality, reflecting the relation of entanglement and the principle of least action. It is shown, that the principle of least action is the self-consistency mechanism of nonlocal causality in relativistic scenarios, especially in timelike scenarios of entangled quanta. From the view of relativistic scenarios, this paper examines the possibility of causal loops in quantum causal relations and investigates quantum causal relations in well established experiments.
A short exposition is given of the foundation of the causal description in classical physics and the failure of the principle of causality in coping with atomic phenomena. It is emphasized that the individuality of the quantum processes excludes a separation between a behaviour of the atomic objects and their interaction with the measuring instruments denning the conditions under which the phenomena appear. This circumstance forces us to recognize a novel relationship, conveniently termed complementarity, between empirical evidence obtained under different experimental conditions. An appropriate tool for a complementary mode of description is provided by the quantum-mechanical formalism which allows us to account for regularities of definite or statistical character beyond the grasp of classical physical explanation. – N. B.