Hagiography and History - The Life of Gregory-Thaumaturgus

Classic

Two-qubit Stabilizer Circuits with Recovery II: Analysis

We study stabilizer circuits that use non-stabilizer qubits and Z-measurements to produce other non-stabilizer qubits. These productions are successful when the correct measurement outcome occurs, but when the opposite outcome is observed, the non-stabilizer input qubit is potentially destroyed. In preceding work [arXiv:1803.06081 (2018)] we introduced protocols able to recreate the expensive non-stabilizer input qubit when the two-qubit stabilizer circuit has an unsuccessful measurement outcome. Such protocols potentially allow a deep computation to recover from such failed measurements without the need to repeat the whole prior computation. Possible complications arise when the recovery protocol itself suffers from a failed measurement. To deal with this, we need to use nested recovery protocols. Here we give a precise analysis of the potential advantage of such recovery protocols as we examine its optimal nesting depth. We show that if the expensive input qubit has cost d, then typically a depth O(log d) recovery protocol is optimal, while a certain special case has optimal depth O(sqrt{d}). We also show that the recovery protocol can achieve a cost reduction by a factor of at most two over circuits that do not use recovery

Two-qubit Stabilizer Circuits with Recovery I: Existence

In this paper, we further investigate the many ways of using stabilizer operations to generate a single qubit output from a two-qubit state. In particular, by restricting the input to certain product states, we discover probabilistic operations capable of transforming stabilizer circuit outputs back into stabilizer circuit inputs. These secondary operations are ideally suited for recovery purposes and require only one extra resource input to proceed. As a result of reusing qubits in this manner, we present an alternative to the original state preparation process that can lower the overall costs of executing a two-qubit stabilizer procedure involving non-stabilizer resources

Towards 3D Facial Reconstruction from Uncalibrated CCTV Footage

Facial comparison in 2D is an accepted method in law enforcement and forensic investigation, but pose variations, varying light conditions and low resolution video data can reduce the evidential value of the comparison. Some of these problems might be solved by comparing 3D face models: a face model derived from CCTV camera footage and a reference face model acquired from a suspect. In our case we will assume uncalibrated CCTV footage, because the original camera setup may be destroyed or replaced after the incident, so precise camera information is no longer available. In contrast to other statistical methods, like Morphable Models, we would like to use no additional statistical information at all. Our method is based on a projective reconstruction of landmarks on the face and an auto-calibration step to obtain a 3D face model in a Euclidean space. In our experiment the effect of the number of frames and noise on the landmarks is explored for 3D face reconstruction based on landmarks. An estimation of the 3D face shape can already be obtained using 25 points in 30 frames

Model-free 3D face shape reconstruction from video sequences

In forensic comparison of facial video data, often only the best quality frontal face frames are selected, and hence much video data is ignored. To improve 2D facial comparison for law enforcement and forensic investigation, we introduce a model-free 3D shape reconstruction algorithm based on 2D landmarks. The algorithm uses around 20 landmarks on the face and combines the structure information of multiple frames. Model based 3D reconstruction methods, such as Morphable Models, reconstruct a 3D face shape model that is strongly biased towards the average face. Therefore, we don't use statistical face shape models in our model-free approach. The 3D landmark reconstruction algorithm simultaneously estimates the shape, pose and position of the face, based only on the fact that all images in the sequence are recorded using a single calibrated camera. The algorithm iteratively updates the reconstruction by including new frames, while maintaining the consistency of the reconstruction. We demonstrate the convergence properties of the method reflected in the 2D reprojection error and the 3D error with respect to a ground truth model. We show that the quality of the reconstruction depends on the noise on the landmarks. In a second experiment we show that the method can be used on realistic face shape data with a styrofoam head model

Exponential speed-up with a single bit of quantum information: Testing the quantum butterfly effect

We present an efficient quantum algorithm to measure the average fidelity decay of a quantum map under perturbation using a single bit of quantum information. Our algorithm scales only as the complexity of the map under investigation, so for those maps admitting an efficient gate decomposition, it provides an exponential speed up over known classical procedures. Fidelity decay is important in the study of complex dynamical systems, where it is conjectured to be a signature of quantum chaos. Our result also illustrates the role of chaos in the process of decoherence.Comment: 4 pages, 2 eps figure

The experiences of people with young-onset dementia : a meta-ethnographic review of the qualitative literature

Dementia is usually diagnosed in later life but can occur in younger people. The experiences of those with older-onset dementia are relatively well understood but little is known about the experiences of those with young-onset dementia (aged less than 65 years). This meta-ethnography therefore synthesised qualitative literature investigating the experiences of people with young-onset dementia (YOD). Six electronic databases were searched and 1155 studies were identified, of which eight fitted the inclusion criteria. These studies were all from Western countries, were mostly recent (2004-2015) and included the experiences of 87 people with YOD. Participants were generally in their fifties or early sixties and were living at home with others. Many reported difficulties both in the process of receiving a diagnosis and afterwards. Diagnosis felt unexpected, 'out of time' and led to changes in self-identity, powerlessness and changes in relationships. Social exclusion was common. Loss of meaningful activity exacerbated a difficult situation. However, the diagnosis did not mean people's lives were over and many with YOD try to regain control by seeking connections with others with the same condition - sometimes a very important source of support. Overall, people living with YOD face unique social challenges which go beyond those of older people living with dementia and which result in an even greater negative impact on their lives. Interventions that facilitate peer support and allow people with YOD to engage in meaningful activity should be developed and could perhaps be provided by the voluntary sector

Molecular techniques reveal cryptic life history and demographic processes of a critically endangered marine turtle

The concept of ‘effective population size’ (Ne), which quantifies how quickly a population will lose genetic variability, is one of the most important contributions of theoretical evolutionary biology to practical conservation management. Ne is often much lower than actual population size: how much so depends on key life history and demographic parameters, such as mating systems and population connectivity, that often remain unknown for species of conservation concern. Molecular techniques allow the indirect study of these parameters, as well as the estimation of current and historical Ne. Here, we use genotyping to assess the genetic health of an important population of the critically endangered hawksbill turtle (Eretmochelys imbricata), a slow-to-mature, difficult-to-observe species with a long history of severe overhunting. Our results were surprisingly positive: we found that the study population, located in the Republic of Seychelles, Indian Ocean, has a relatively large Ne, estimated to exceed 1000, and showed no evidence of a recent reduction in Ne (i.e. no genetic bottleneck). Furthermore, molecular inferences suggest the species' mating system is conducive to maintaining a large Ne, with a relatively large and widely distributed male population promoting considerable gene flow amongst nesting sites across the Seychelles area. This may also be reinforced by the movement of females between nesting sites. Our study underlines how molecular techniques can help to inform conservation biology. In this case our results suggest that this important hawksbill population is starting from a relatively strong position as it faces new challenges, such as global climate change