56 research outputs found
The superadditivity effects of quantum capacity decrease with the dimension for qudit depolarizing channels
Quantum channel capacity is a fundamental quantity in order to understand how
good can quantum information be transmitted or corrected when subjected to
noise. However, it is generally not known how to compute such quantities, since
the quantum channel coherent information is not additive for all channels,
implying that it must be maximized over an unbounded number of channel uses.
This leads to the phenomenon known as superadditivity, which refers to the fact
that the regularized coherent information of channel uses exceeds one-shot
coherent information. In this article, we study how the gain in quantum
capacity of qudit depolarizing channels relates to the dimension of the systems
considered. We make use of an argument based on the no-cloning bound in order
to proof that the possible superadditive effects decrease as a function of the
dimension for such family of channels. In addition, we prove that the capacity
of the qudit depolarizing channel coincides with the coherent information when
. We conclude that when high dimensional qudits
experiencing depolarizing noise are considered, the coherent information of the
channel is not only an achievable rate but essentially the maximum possible
rate for any quantum block code.Comment: 7 pages, 2 figure
Very short-term parametric ambient temperature confidence interval forecasting to compute key control parameters for photovoltaic generators
Performance enhancement of surface codes via recursive MWPM decoding
The minimum weight perfect matching (MWPM) decoder is the standard decoding
strategy for quantum surface codes. However, it suffers a harsh decrease in
performance when subjected to biased or non-identical quantum noise. In this
work, we modify the conventional MWPM decoder so that it considers the biases,
the non-uniformities and the relationship between , and errors of
the constituent qubits of a given surface code. Our modified approach, which we
refer to as the recursive MWPM decoder, obtains an improvement in the
probability threshold under depolarizing noise. We also obtain
significant performance improvements when considering biased noise and
independent non-identically distributed (i.ni.d.) error models derived from
measurements performed on state-of-the-art quantum processors. In fact, when
subjected to i.ni.d. noise, the recursive MWPM decoder yields a performance
improvement of over the conventional MWPM strategy and, in some
cases, it even surpasses the performance obtained over the well-known
depolarizing channel
Decoding algorithms for surface codes
Quantum technologies have the potential to solve computationally hard
problems that are intractable via classical means. Unfortunately, the unstable
nature of quantum information makes it prone to errors. For this reason,
quantum error correction is an invaluable tool to make quantum information
reliable and enable the ultimate goal of fault-tolerant quantum computing.
Surface codes currently stand as the most promising candidates to build error
corrected qubits given their two-dimensional architecture, a requirement of
only local operations, and high tolerance to quantum noise. Decoding algorithms
are an integral component of any error correction scheme, as they are tasked
with producing accurate estimates of the errors that affect quantum
information, so that it can subsequently be corrected. A critical aspect of
decoding algorithms is their speed, since the quantum state will suffer
additional errors with the passage of time. This poses a connundrum-like
tradeoff, where decoding performance is improved at the expense of complexity
and viceversa. In this review, a thorough discussion of state-of-the-art
surface code decoding algorithms is provided. The core operation of these
methods is described along with existing variants that show promise for
improved results. In addition, both the decoding performance, in terms of error
correction capability, and decoding complexity, are compared. A review of the
existing software tools regarding surface code decoding is also provided.Comment: 54 pages, 31 figure
Immunosenescence in multiple sclerosis: the identification of new therapeutic targets
Autoimmunitat; ImmunosenescĂšncia; Esclerosi mĂșltipleAutoinmunidad; Inmunosenescencia; Esclerosis mĂșltipleAutoimmunity; Immunosenescence; Multiple sclerosisThe number of elderly multiple sclerosis (MS) patients is growing, mainly due to the increase in the life expectancy of the general population and the availability of effective disease-modifying treatments. However, current treatments reduce the frequency of relapses and slow the progression of the disease, but they cannot stop the disability accumulation associated with disease progression. One possible explanation is the impact of immunosenescence, which is associated with the accumulation of unusual immune cell subsets that are thought to have a role in the development of an early ageing process in autoimmunity. Here, we provide a recent overview of how senescence affects immune cell function and how it is involved in the pathogenesis of autoimmune diseases, particularly MS. Numerous studies have demonstrated age-related immune changes in experimental autoimmune encephalomyelitis models, and the premature onset of immunosenescence has been demonstrated in MS patients. Therefore, potential therapeutic strategies based on rejuvenating the immune system have been proposed. Senolytics and regenerative strategies using haematopoietic stem cells, therapies based on rejuvenating oligodendrocyte precursor cells, microglia and monocytes, thymus cells and senescent B and T cells are capable of reversing the process of immunosenescence and could have a beneficial impact on the progression of MS.This work was supported by the Fondo de InvestigaciĂłn Sanitaria, Instituto de Salud Carlos III , and co-funded by the European Union ( European Regional Development Fund / European Social Fund ), âA way to build Europeâ, under Grant PI18/01146 and RD16/0015/004 and the â AgĂšncia de GestiĂł d'Ajuts Universitaris i de Recerca â (AGAUR; Generalitat de Catalunya ) under Grant 2017SGR527
Multi-qubit time-varying quantum channels for NISQ-era superconducting quantum processors
Recent experimental studies have shown that the relaxation time () and
the dephasing time () of superconducting qubits fluctuate considerably
over time. To appropriately consider this time-varying nature of the and
parameters, a new class of quantum channels, known as Time-Varying
Quantum Channels (TVQCs), has been proposed. In previous works, realizations of
multi-qubit TVQCs have been assumed to be equal for all the qubits of an error
correction block, implying that the random variables that describe the
fluctuations of and are block-to-block uncorrelated, but qubit-wise
perfectly correlated for the same block. Physically, the fluctuations of these
decoherence parameters are explained by the incoherent coupling of the qubits
with unstable near-resonant two-level-systems (TLS), which indicates that such
variations may be local to each of the qubits of the system. In this article,
we perform a correlation analysis of the fluctuations of the relaxation times
of multi-qubit quantum processors ibmq\_quito, ibmq\_belem, ibmq\_lima,
ibmq\_santiago and ibmq\_bogota. Our results show that it is reasonable to
assume that the fluctuations of the relaxation and dephasing times of
superconducting qubits are local to each of the qubits of the system. Based on
these results, we discuss the multi-qubit TVQCs when the fluctuations of the
decoherence parameters for an error correction block are qubit-wise
uncorrelated (as well as from block-to-block), a scenario we have named the
Fast Time-Varying Quantum Channel (FTVQC). Furthermore, we lower bound the
quantum capacity of general FTVQCs based on a quantity we refer to as the
ergodic quantum capacity. Finally, we use numerical simulations to study the
performance of quantum error correction codes (QECC) when they operate over
FTVQCs.Comment: 21 page
Multiqubit time-varying quantum channels for NISQ-era superconducting quantum processors
Time-varying quantum channels (TVQCs) have been proposed as a model to include fluctuations of the relaxation (T1) and dephasing times (T2). In previous works, realizations of multiqubit TVQCs have been assumed to be equal for all the qubits of an error correction block, implying that the random variables that describe the fluctuations of T1 and T2 are block-to-block uncorrelated but qubit-wise perfectly correlated for the same block. In this article, we perform a correlation analysis of the fluctuations of the relaxation times of five multiqubit quantum processors. Our results show that it is reasonable to assume that the fluctuations of the relaxation and dephasing times of superconducting qubits are local to each of the qubits of the system. Based on these results, we discuss the multiqubit TVQCs when the fluctuations of the decoherence parameters for an error correction block are qubit-wise uncorrelated (as well as from block-to-block), a scenario we have named the fast time-varying quantum channel (FTVQC). Furthermore, we lower-bound the quantum capacity of general FTVQCs based on a quantity we refer to as the ergodic quantum capacity. Finally, we use numerical simulations to study the performance of quantum error correction codes when they operate over FTVQCs.This work was supported by the Spanish Ministry of Econ-omy and Competitiveness through the ADELE project (Grant No. PID2019-104958RB-C44), by the Spanish Ministry of Science and Innovation through the proyect. Few-qubit quantum hardware, algorithms and codes, on photonic and solid-state systems (PLEC2021-008251), by the DiputaciĂłn Foral de Gipuzkoa through the DECALOQC Project No. E 190 / 2021 (ES), by the Ministry of Economic Affairs and Digital Transformation of the Spanish Government through the QUANTUM ENIA project call - QUANTUM SPAIN project, and by the European Union through the Recov-ery, Transformation and Resilience Plan - NextGenerationEU within the framework of the Digital Spain 2025 Agenda. This work was funded in part by NSF Award No. CCF-2007689. This work was partly funded by the Spanish Ministry of Economy and Competitiveness through the MADDIE project (Grants No. PID2022-137099NB-C41 and No. PID2022- 137099NB-C44).Peer ReviewedPostprint (published version
Social Economy in the Basque Country
In the social economy area and, more concretely, in the cooperative field, the Basque Country has, no doubt unintentionally, become a worldwide benchmark. The dynamism that energizes Basque social initiatives has resulted in outstanding examples of good practices where firms' priorities are guided by social aims that respond to social needs, steering clear of the commercial profit mechanisms that are the main global driver of private economic initiative. This work, in nine chapters, addresses a wide range of contemporary aspects of the contemporary Basque social sector; legal framework; reality and development in the Autonomous Community of Euskadi; promotion of the Social Economy in Navarre; typology of public policies for the advancement of the Social Economy in Europe; associated work cooperatives in the Northern Basque Country; viability of globalization of cooperatives without risking loss of their hallmark principles and values; and tenant cooperatives. With this book we hope to make a modest contribution to encourage knowledge and reflection on the rich and complex dynamic that informs the Basque social economy today.This book looks at the social economy in the Basque Country, gathering scholars on the social economic structure, its framework, public policies and the viability of globalization of cooperative.This book was published with generous financial support from the Basque Government
An epidemiological model for prediction of endometrial cancer risk in Europe
Endometrial cancer (EC) is the fourth most frequent cancer in women in Europe, and as its incidence is increasing, prevention strategies gain further pertinence. Risk prediction models can be a useful tool for identifying women likely to benefit from targeted prevention measures. On the basis of data from 201,811 women (mostly aged 30â65 years) including 855 incident EC cases from eight countries in the European Prospective Investigation into Cancer and Nutrition cohort, a model to predict EC was developed. A step-wise model selection process was used to select confirmed predictive epidemiologic risk factors. Piece-wise constant hazard rates in 5-year age-intervals were estimated in a cause-specific competing risks model, five-fold-cross-validation was applied for internal validation. Risk factors included in the risk prediction model were body-mass index (BMI), menopausal status, age at menarche and at menopause, oral contraceptive use, overall and by different BMI categories and overall duration of use, parity, age at first full-term pregnancy, duration of menopausal hormone therapy and smoking status (specific for pre, peri- and post-menopausal women). These variables improved the discriminating capacity to predict risk over 5 years from 71 % for a model based on age alone to 77 % (overall C statistic), and the model was well-calibrated (ratio of expected to observed cases = 0.99). Our model could be used for the identification of women at increased risk of EC in Western Europe. To achieve an EC-risk model with general validity, a large-scale cohort-consortium approach would be needed to assess and adjust for population variation
Empty Urbanism: the bursting of the Spanish housing bubble
The depth of the Spanish housing crisis manifests itself in the collapse of construction activity and in the amount of housing and land stocks. The geography of the crisis shows its widespread nature, and the intensity of the previous bubble explains spatial differences. Resulting from this collapse are some problematic areas of 'empty urbanism'. An enormous land bubble, emerging from the peculiar Spanish urban development model, was a key factor in the impacts - caused by the crisis - on the territory and land-use plans. The crisis has demonstrated the unsustainability of this and the urgency of change in the existing land-use plans
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