60 research outputs found
Currencies in resource theories
How may we quantify the value of physical resources, such as entangled
quantum states, heat baths or lasers? Existing resource theories give us
partial answers; however, these rely on idealizations, like perfectly
independent copies of states or exact knowledge of a quantum state. Here we
introduce the general tool of currencies to quantify realistic descriptions of
resources, applicable in experimental settings when we do not have perfect
control over a physical system, when only the neighbourhood of a state or some
of its properties are known, or when there is no obvious way to decompose a
global space into subsystems. Currencies are a special set of resources chosen
to quantify all others - like Bell pairs in LOCC or a lifted weight in
thermodynamics. We show that from very weak assumptions on the theory we can
already find useful currencies that give us necessary and sufficient conditions
for resource conversion, and we build up more results as we impose further
structure. This work is an application of Resource theories of knowledge
[arXiv:1511.08818], generalizing axiomatic approaches to thermodynamic entropy,
work and currencies made of local copies.Comment: 13 pages + appendix. Contains a one-page summary of the paper
Resource theories of knowledge [arXiv:1511.08818
Extremal distributions under approximate majorization
Although an input distribution may not majorize a target distribution, it may majorize a distribution which is close to the target. Here we consider a notion of approximate majorization. For any distribution, and given a distance δ, we find the approximate distributions which majorize (are majorized by) all other distributions within the distance δ. We call these the steepest and flattest approximation. This enables one to compute how close one can get to a given target distribution under a process governed by majorization. We show that the flattest and steepest approximations preserve ordering under majorization. Furthermore, we give a notion of majorization distance. This has applications ranging from thermodynamics, entanglement theory, and economics
NOMA-based improper signaling for multicell MISO RIS-assisted broadcast channels
In this paper, we study the performance of reconfigurable intelligent surfaces (RISs) in a multicell broadcast channel (BC) that employs improper Gaussian signaling (IGS) jointly with non-orthogonal multiple access (NOMA) to optimize either the minimum-weighted rate or the energy efficiency (EE) of the network. We show that although the RIS can significantly improve the system performance, it cannot mitigate interference completely, so we have to employ other interference-management techniques to further improve performance. We show that the proposed NOMA-based IGS scheme can substantially outperform proper Gaussian signaling (PGS) and IGS schemes that treat interference as noise (TIN) in particular when the number of users per cell is larger than the number of base station (BS) antennas (referred to as overloaded networks). In other words, IGS and NOMA complement to each other as interference management techniques in multicell RIS-assisted BCs. Furthermore, we consider three different feasibility sets for the RIS components showing that even a RIS with a small number of elements provides considerable gains for all the feasibility sets.The associate editor coordinating the review of this manuscript and approving it for publication was Prof. Sangarapillai Lambotharan. The work of Ignacio Santamaria was supported by the Project ADELE funded by MCIN/ AEI /10.13039/501100011033, under Grant PID2019-104958RB-C43. The work of Eduard Jorswieck was supported by the Federal Ministry of Education and Research (BMBF, Germany) through the Program of Souverän. Digital. Vernetzt.” joint Project 6G-RIC, under Grants 16KISK020K and 16KISK031
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