Quantum theory in finite dimension cannot explain every general process with finite memory

Arguably, the largest class of stochastic processes generated by means of a finite memory consists of those that are sequences of observations produced by sequential measurements in a suitable generalized probabilistic theory (GPT). These are constructed from a finite-dimensional memory evolving under a set of possible linear maps, and with probabilities of outcomes determined by linear functions of the memory state. Examples of such models are given by classical hidden Markov processes, where the memory state is a probability distribution, and at each step it evolves according to a non-negative matrix, and hidden quantum Markov processes, where the memory state is a finite dimensional quantum state, and at each step it evolves according to a completely positive map. Here we show that the set of processes admitting a finite-dimensional explanation do not need to be explainable in terms of either classical probability or quantum mechanics. To wit, we exhibit families of processes that have a finite-dimensional explanation, defined manifestly by the dynamics of explicitly given GPT, but that do not admit a quantum, and therefore not even classical, explanation in finite dimension. Furthermore, we present a family of quantum processes on qubits and qutrits that do not admit a classical finite-dimensional realization, which includes examples introduced earlier by Fox, Rubin, Dharmadikari and Nadkarni as functions of infinite dimensional Markov chains, and lower bound the size of the memory of a classical model realizing a noisy version of the qubit processes.Comment: 18 pages, 0 figure

Efficient unitary approximations in quantum computing: the Solovay-Kitaev theorem

Treballs Finals de Grau de Matemàtiques, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2019, Director: Joana Cirici[en] Over the past few years, quantum computing has become more plausible due to the great advances in technology. While quantum computers are on their birth, the underlying mathematics have evolved to the point of proving that some quantum algorithms can solve problems that were unsolvable in classic computers. In order to implement these algorithms in a real machine, it is important to develop efficient ways to do it. The Solovay-Kitaev Theorem states that is possible. This work pretends to offer a complete review of the Solovay- Kitaev Theorem giving all the necessary tools to prove it. Moreover, we offer a brief introduction to the standard mathematical model of quantum computing, based on unitary operations

Scaling of the energy and entropy errors in quantum circuits

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2019, Tutor: José Ignacio LatorreQuantum algorithms based on simulating states of a quantum system cannot simulate these states without an error. This work studies the relations between the error of an approximated quantum circuit that simulates the ground state of a Hamiltonian and the error of the energy and Von Neumann entropy of this state. In addition, we relate the errors with the gate cost of the approximated quantum circuit using the Solovay-Kitaev theore

Scaling of variational quantum circuit depth for condensed matter systems

We benchmark the accuracy of a variational quantum eigensolver based on a finite-depth quantum circuit encoding ground state of local Hamiltonians. We show that in gapped phases, the accuracy improves exponentially with the depth of the circuit. When trying to encode the ground state of conformally invariant Hamiltonians, we observe two regimes. A finite-depth regime, where the accuracy improves slowly with the number of layers, and a finite-size regime where it improves again exponentially. The cross-over between the two regimes happens at a critical number of layers whose value increases linearly with the size of the system. We discuss the implication of these observations in the context of comparing different variational ansatz and their effectiveness in describing critical ground states

Thymus vulgaris subsp. mansanetianus subsp. nov. (Lamiaceae)

Se describe una nueva subespecie de Thymus vulgaris L. (Lamiaceae); Th. vulgaris subsp. mansanetianus subsp. nov., caracterizada por presentar un hábito postrado, tallos estoloníferos, decumbentes y radicantes, hojas muy estrechas y una floración otoñal

Effect of the heat dissipation system on hard-switching GaN-based power converters for energy conversion

The design of a cooling system is critical in power converters based on wide-bandgap (WBG) semiconductors. The use of gallium nitride enhancement-mode high-electron-mobility transistors (GaN e-HEMTs) is particularly challenging due to their small size and high power capability. In this paper, we model, study and compare the different heat dissipation systems proposed for high power density GaN-based power converters. Two dissipation systems are analysed in detail: bottom-side dissipation using thermal vias and top-side dissipation using different thermal interface materials. The effectiveness of both dissipation techniques is analysed using MATLAB/Simulink and PLECS. Furthermore, the impact of the dissipation system on the parasitic elements of the converter is studied using advanced design systems (ADS). The experimental results of the GaN-based converters show the effectiveness of the analysed heat dissipation systems and how top-side cooled converters have the lowest parasitic inductance among the studied power converters.This work was supported by the Industrial Doctorates Plan of the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya, the Centro para el Desarrollo Tecnológico Industrial (IDI-20200864), and the Ministerio de Ciencia, Innovación y Universidades of Spain within the project PID2019-111420RB-I00Peer ReviewedPostprint (published version

Sobre l’enquadrament sintaxonòmic dels brugars valencians

Es realitza una nova proposta sintaxonòmica per a les comunitats dominades per Erica scoparia i Erica arborea dels sectors Setabenc i Valenciano-Tarraconenc (província Catalano-Provençal-Balear), amb la descripció de les associacions Thymo piperellae-Ericetum scopariae i Centaureo saguntinae-Ericetum arboreae, de les quals es fa una caracterització florística, ecològica i corològica.A new syntaxonomic proposal is made for the communities dominated by Erica scoparia and Erica arborea in the Setabensian and Valencian-Tarraconensian sector (Catalonian-Provencian-Balear province), with the description of the associations Thymo piperellae-Ericetum scopariae and Centaureo saguntinae-Ericetum arboreae, and which floristic, ecologic and chorologic characteristics are defined

Preserved Error-Monitoring in Borderline Personality Disorder Patients with and without Non-Suicidal Self-Injury Behaviors

Background: The presence of non-suicidal self-injury acts in Borderline Personality Disorder (BPD) is very prevalent. These behaviors are a public health concern and have become a poorly understood phenomenon in the community. It has been proposed that the commission of non-suicidal self-injury might be related to a failure in the brain network regulating executive functions. Previous studies have shown that BPD patients present an impairment in their capacity to monitor actions and conflicts associated with the performance of certain actions, which suppose an important aspect of cognitive control. Method: We used Event Related Potentials to examine the behavioral and electrophysiological indexes associated with the error monitoring in two BPD outpatients groups (17 patients each) differentiated according to the presence or absence of non-suicidal self-injury behaviors. We also examined 17 age- and intelligence- matched healthy control participants. Results: The three groups did not show significant differences in event-related potentials associated with errors (Error-Related Negativity and Pe) nor in theta power increase following errors. Conclusions: This is the first study investigating the behavioral and electrophysiological error monitoring indexes in BPD patients characterized by their history of non-suicidal self-injury behaviors. Our results show that error monitoring is preserved in BPD patients and suggest that non-suicidal self-injury acts are not related to a dysfunction in the cognitive control mechanisms

Conservation status of Narcissus perezlarae Font Quer (Amaryllidaceae) in the Valencian Community

Narcissus perezlarae está incluido en el Catálogo Valenciano de Especies de Flora Amenazadas de la Comunidad Valenciana (Orden 6/2013) en la categoría "En peligro de extinción". Estudios recientes han demostrado su origen híbrido (= N. cavanillesii × N. miniatus [= N. serotinus auct.]). Por otro lado, el mayor especialista y monografía del género reclamó recientemente su autonomía como especie independiente, como N. piifontianus. Esta especie es endémica de la península Ibérica, presente en Alto Alentejo (Portugal), Sevilla y Cádiz (España), y en la parte oriental de la Cordillera Bética, entre Alicante y Valencia. Sin embargo, si se tratara como una especie independiente, sería un endemismo exclusivamente restringido a la Comunidad Valenciana. Siete poblaciones naturales han sido monitoreadas, cuyos datos censales oscilan anualmente. El último censo contiene 1.634 plantas. Desde 2010, se han llevado a cabo cinco experiencias de translocación en la provincia de Alicante. De un total de 8.970 ejemplares introducidos se ha registrado una tasa de supervivencia del 28,4% (2.545 plantas) en el último censo. Las poblaciones recién creadas aumentan el número de localidades conocidas de la especie en la Comunidad Valenciana y amplían considerablemente su distribución a lo largo del territorio.Narcissus perezlarae is included in the Valencian Catalogue of Threatened Species of the Valencian Community (Order 6/2013) in the category "In danger of extinction". Recent studies have demonstrated its hybridogenic origin (= N. cavanillesii × N. miniatus [= N. serotinus auct.]). On the other hand, the greatest specialist and monograph of the genus has most recently claimed its autonomy as an independent species, as N. piifontianus. This species is endemic to the Iberian Peninsula, present in Alto Alentejo (Portugal), Sevilla and Cadiz (Spain), and in the eastern part of the Baetic Mountains, between Alicante and Valencia. However, if treated as an independent species, it would be an endemism exclusively restricted to the Valencian Community. Seven natural populations have been monitored, whose census data oscillate annually. The latest census contains 1634 plants. Since 2010, five translocation experiences have been carried out in Alicante province. A total amount of 8,970 plants were translocated and a survival rate of 28,4% (2,545 plants) was observed in the latest census. The newly created populations increase the number of known locations of the species in the Valencian Community and considerably expand their distribution range along the territory