Quantum measurement optimization by decomposition of measurements into extremals

Using the convex structure of positive operator value measurements and of several quantities used in quantum metrology, such as quantum Fisher information or the quantum Van Trees information, we present an efficient numerical method to find the best strategy allowed by quantum mechanics to estimate a parameter. This method explores extremal measurements thus providing a significant advantage over previously used methods. We exemplify the method for different cost functions in a qubit and in a harmonic oscillator and find a strong numerical advantage when the desired target error is sufficiently small.Comment: 12 page

The importance of financial accounting in Business Administration and Management degrees at the Spanish universities

Este trabajo tiene como objetivo analizar si en el grado más ofertado por las universidades españolas como es el de Administración y Dirección de Empresas, puede haber diferencias relevantes de contenido, centrándonos en una de las áreas que forma parte de su columna vertebral como es la contabilidad y, más concretamente, la contabilidad financiera. Valoramos los créditos impartidos en todas la universidades, tanto públicas como privadas, comprobando que hay diferencias significativas y destacando aquellas en las que la materia adquiere una notable relevancia acorde con la importancia que tradicionalmente ha tenido en estos estudios (Sevilla, Almería, Granada, Pablo de Olavide, Las Palmas, León, Europea de Madrid, UNED, Navarra, Alicante, Extremadura, La Coruña, Islas Baleares, La Rioja, Miguel Hernández, Zaragoza, Cantabria, País Vasco, UDIMA, Murcia y Santiago de Compostela), frente a las que han reducido su presencia a la mínima expresión (Carlos III, IE Universidad, Autónoma de Barcelona, Valencia y Oviedo), lo que puede suponer una formación muy dispar dependiendo de la localización de la universidad. También se pone de manifiesto que las universidades que han ofertado de forma paralela el nuevo grado de Finanzas y Contabilidad han perdido peso en contabilidad financiera pero no de forma relevante.This study aims to analyse if in the most offered degree by Spanish universities, that is Business Administration and Management, there may be significant differences in content. We focus on one area that is part of its vertebral column such as the accounting and, more specifically, financial accounting. We make a valuation of taught credits in the state and private universities, observing that there are significant differences. We highlight those in which the subject acquires a remarkable relevance in agreement with the importance that it has traditionally had in these studies (Sevilla, Almería, Granada, Pablo de Olavide, Las Palmas, León, Europea de Madrid, UNED, Navarra, Alicante, Extremadura, La Coruña, Islas Baleares, La Rioja, Miguel Hernández, Zaragoza, Cantabria, País Vasco, UDIMA, Murcia y Santiago de Compostela), versus those that have reduced their presence to the bare minimum (Carlos III, IE Universidad, Autónoma de Barcelona, Valencia y Oviedo). This situation might cause a very different formation depending on the location of universities. This paper also shows that the universities that offer the new Finance and Accounting degree at the same time that ADE degree have influenced negatively in the financial accounting but not in a relevant way

Verification of Quantum Stable Sources

We introduce the problem of verification of stable sources in quantum systems. This problem is closely related to the problem of quantum verification first proposed by Pallister et. al. [1], however it extends the notion of the original problem. We introduce a family of states that come from a non-i.i.d. source which we call a Markov state. We prove in theorem 1 that these states are not well described with tensor products over a changing source. In theorem 2 we further provide a lower bound on the trace distance between two Markov states, which is the simplest way to solve the problem of verification of quantum stable sources.Comment: 6 pages, 4 figure

Classicality from Quantum Stochastic Processes

We develop a theory of classicality from quantum systems. This theory stems from the study of classical and quantum stationary stochastic processes. The stochastic processes are characterized by polyhedral (classical) and semidefinite representative (quantum) cones. Based on a previous result \cite{2209.06806v1} we expand the study of fixed points from quantum channels. We give a semidefinite program that characterizes a quantum channel separating into a core and a part that decays with many iterations. In general, the solution is non-separable in the space it is defined. We present a characterization of channels in terms of their fixed points for the separable case. A quantum simulation of a polyhedral cone can then be constructed.Comment: 12 pages, 1 figur

Quantum Stabilizer Channel for Thermalization

We study the problem of quantum thermalization from a very recent perspective: via discrete interactions with thermalized systems. We thus extend the previously introduced scattering thermalization program by studying not only a specific channel but allowing any possible one. We find a channel that solves a fixed point condition using the Choi matrix approach that is in general non-trace-preserving. We also find a general way to complement the found channel so that it becomes trace-preserving. Therefore we find a general way of characterizing a family of channels with the same desired fixed point. From a quantum computing perspective, the results thus obtained can be interpreted as a condition for quantum error correction that also reminds of quantum error avoiding.Comment: 6 pages,1 figur

Sequential Analysis of Chunks of Pure Qubits

We investigate an advantage for information processing of ordering a set of states over making a global quantum measurement with a fixed number of copies. The setting that we want to investigate is clearer if we introduce Alice and Bob, as usual. Suppose Alice has $N<\infty$ copies of one of two quantum states $\sigma_0$ or $\sigma_1$ and she gives this states to Bob. We find that there are situations where Bob has to make chunks of $l$ states and process them sequentially to optimally distinguish the two hypotheses. We find an expression for the optimal $l$ given some desired error constraints in the case of pure qubits. The results presented here also have relevance in the "it from qubit" program in the sense that they suggest that time arises from information processing.Comment: 5 pages, 2 figure