Modeling quantum noise for efficient testing of fault-tolerant circuits

Understanding fault-tolerant properties of quantum circuits is important for the design of large-scale quantum information processors. In particular, simulating properties of encoded circuits is a crucial tool for investigating the relationships between the noise model, encoding scheme, and threshold value. For general circuits and noise models, these simulations quickly become intractable in the size of the encoded circuit. We introduce methods for approximating a noise process by one which allows for efficient Monte Carlo simulation of properties of encoded circuits. The approximations are as close to the original process as possible without overestimating their ability to preserve quantum information, a key property for obtaining more honest estimates of threshold values. We numerically illustrate the method with various physically relevant noise models.Comment: 6 pages, 1 figur

Quantum Gate Fidelity in Terms of Choi Matrices

We provide new results for computing and comparing the quantum gate fidelity of quantum channels via their Choi matrices. We extend recent work that showed there exist non-dual pairs of quantum channels with equal gate fidelity by providing an explicit characterization of all such channels. We use our characterization to show that when the dimension is 2 (or 3, under slightly stronger hypotheses), the gate fidelity of two channels is equal if and only if their difference equals the difference of some unital map and its dual -- a fact that has been shown to be false when the dimension is 4 or larger. We also present a formula for the minimum gate fidelity of a channel in terms of a well-studied norm on a compression of its Choi matrix. As a consequence, several new ways of bounding and approximating the minimum gate fidelity follow, including a simple semidefinite program to compute it for qubit channels.Comment: Minor corrections and updates since v1. 16 pages, 1 figur

Visual outcome in pediatric uveitis: A retrospective data review in 277 children

Purpose: This study aimed to describe visual outcomes in cases of pediatric uveitis in an Indian population and to analyze various factors affecting these outcomes. Methods: Single-center, retrospective chart review of 277 cases of uveitis in patients under the age of 18 years. Variables assessed included age and sex distribution, anatomical location of uveitis, systemic associations, complications, and various treatment strategies used, including long-term immunomodulation and surgical management of complications if required. The main outcome was the final visual acuity. Results: At the final visit, 51.5% of the eyes showed improvement in the final visual acuity, while vision remained stable in 28.7% and 19.7% of the eyes showed worsening of vision at the final follow-up. A total of 19.4% of patients were blind in at least one eye at the final visit, and 16 patients (5.77%) remained bilaterally blind at the final follow-up. The presence of cataract (p = 0), posterior uveitis (p = 0.005), and retinal detachment (p = 0.014) were the most significant risk factors for predicting worse visual outcomes. More than half (65.7%) of patients reported a complication at some point in their follow-up, and the most common complication was cataract. In total, 50.9% of patients required long-term immunomodulatory therapy. Conclusion: Pediatric uveitis remains a challenging condition to treat and follow-up, and the visual outcome remains guarded for most patients

Preferential attachment of Escherichia coli to different particle size fractions of an agricultural grassland soil.

This study reports on the attachment preference of a faecally derived bacterium, Escherichia coli, to soil particles of defined size fractions. In a batch sorption experiment using a clay loam soil it was found that 35% of introduced E. coli cells were associated with soil particulates >2 μm diameter. Of this 35%, most of the E. coli (14%) were found to be associated with the size fraction 15-4 μm. This was attributed to the larger number of particles within this size range and its consequently greater surface area available for attachment. When results were normalised with respect to estimates of the surface area available for bacterial cell attachment to each size fraction, it was found that E. coli preferentially attached to those soil particles within the size range 30-16 μm. For soil particles > 2 μm, E. coli showed at least 3.9 times more preference to associate with the 30-16 μm than any other fraction. We report that E. coli can associate with different soil particle size fractions in varying proportions and that this is likely to impact on the hydrological transfer of cells through soil and have clear implications for our wider understanding of the attachment dynamics of faecally derived bacteria in soils of different compositions