Computation in generalised probabilisitic theories

From the general difficulty of simulating quantum systems using classical systems, and in particular the existence of an efficient quantum algorithm for factoring, it is likely that quantum computation is intrinsically more powerful than classical computation. At present, the best upper bound known...

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Veröffentlicht in:New journal of physics Jg. 17; H. 8; S. 83001 - 83020
Hauptverfasser: Lee, Ciarán M, Barrett, Jonathan
Format: Journal Article
Sprache:Englisch
Veröffentlicht: Bristol IOP Publishing 03.08.2015
Schlagworte:
Algorithms
Circuits
Complexity
Computation
Computational efficiency
Computer simulation
foundations of quantum theory
generalised probabilisitic theories
Inclusions
Information theory
Optimization
Physics
Polypropylenes
quantum computation
Quantum computing
Quantum theory
Upper bounds
ISSN:1367-2630, 1367-2630
Online-Zugang:Volltext
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Zusammenfassung:From the general difficulty of simulating quantum systems using classical systems, and in particular the existence of an efficient quantum algorithm for factoring, it is likely that quantum computation is intrinsically more powerful than classical computation. At present, the best upper bound known for the power of quantum computation is that , where is a classical complexity class (known to be included in , hence ). This work investigates limits on computational power that are imposed by simple physical, or information theoretic, principles. To this end, we define a circuit-based model of computation in a class of operationally-defined theories more general than quantum theory, and ask: what is the minimal set of physical assumptions under which the above inclusions still hold? We show that given only an assumption of tomographic locality (roughly, that multipartite states and transformations can be characterized by local measurements), efficient computations are contained in . This inclusion still holds even without assuming a basic notion of causality (where the notion is, roughly, that probabilities for outcomes cannot depend on future measurement choices). Following Aaronson, we extend the computational model by allowing post-selection on measurement outcomes. Aaronson showed that the corresponding quantum complexity class, , is equal to . Given only the assumption of tomographic locality, the inclusion in still holds for post-selected computation in general theories. Hence in a world with post-selection, quantum theory is optimal for computation in the space of all operational theories. We then consider whether one can obtain relativized complexity results for general theories. It is not obvious how to define a sensible notion of a computational oracle in the general framework that reduces to the standard notion in the quantum case. Nevertheless, it is possible to define computation relative to a 'classical oracle'. Then, we show there exists a classical oracle relative to which efficient computation in any theory satisfying the causality assumption does not include .
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ISSN:1367-2630
1367-2630
DOI:10.1088/1367-2630/17/8/083001