Speeding up Thermalisation via Open Quantum System Variational Optimisation

Optimizing open quantum system evolution is an important step on the way to achieving quantum computing and quantum thermodynamic tasks. In this article, we approach optimisation via variational principles and derive an open quantum system variational algorithm explicitly for Lindblad evolution in Liouville space. As an example of such control over open system evolution, we control the thermalisation of a qubit attached to a thermal Lindbladian bath with a damping rate $\gamma$. Since thermalisation is an asymptotic process and the variational algorithm we consider is for fixed time, we present a way to discuss the potential speedup of thermalisation that can be expected from such variational algorithms.Comment: 10 pages, 4 figures, comments welcom

Comparative effectiveness of sitagliptin and vildagliptin in the management of patients with type 2 diabetes mellitus undergoing haemodialysis: an Indian rural tertiary care centre experience

Background: The prevalence of chronic kidney disease is increasing with diabetic nephropathy as the common underlying cause. Although numerous drugs are being used to improve glycaemic control, evidence in patients with diabetic nephropathy is sparse. The aim of the present was to evaluate the effectiveness of sitagliptin or vildagliptin addition on glycaemic control in patients with T2DM undergoing haemodialysis as part of their routine care in a rural tertiary care setting.Methods: Type 2 diabetic patients on maintenance haemodialysis as part of routine care and whose glycaemia was not controlled adequately and prescribed one of the oral gliptins once daily in addition to existing therapy for a period of 24 weeks were included in the present study. Effectiveness was assessed in terms of glycaemic control as measured by the change over time in glycated haemoglobin. Data analysis included glycated haemoglobin, body weight, serum creatinine, urine albumin creatinine ratio and the occurrence of hypoglycaemia.Results: Significant reduction in glycated haemoglobin values were noted after 24 weeks of therapy with gliptins similar to insulin glargine with a small weight loss. There was an insignificant decrease in the serum creatinine and urine albumin excretion levels after treatment with vildagliptin with Vildagliptin producing a slightly higher decrease but there was no correlation with changes in A1c levels. The overall incidence of adverse experiences was low and generally mild in both groups.Conclusions: In a group of Asian Indian patients with diabetic nephropathy due to T2DM undergoing haemodialysis in whom glycaemia was not controlled adequately, addition of gliptins helped to achieve glycaemic control to a similar extent as insulin glargine but with a marginal weight advantage

Phase change materials in light modulating applications beyond data storage

Invited paper presented at the European\Phase Change and Ovonics Symposium 2015, 2015-09-06, 2015-09-08, AmsterdamThe use of phase change materials in applications that manipulate light reflectivity and transmissivity would appear to be both obvious and completely infeasible at the same time. It is obvious simply because many of these materials were developed with the primary aim of being able to store optically accessible data, which relied on the optical refractive index contrast between the two reversibly accessible solid states of the material. It would appear infeasible upon further consideration because, not only is the change in the refractive index not very large in the visible wavelengths, but also because the absorption of the material in both states resembles a metallic element as opposed to a dielectric, which would greatly reduce contrast. Over the last two and a half years, we have combined thin film optics concepts with phase change materials to essentially enable the use of such materials in light modulation applications such as displays, smart glazing and security markings. In this abstract, we also show some additional work done on two types of phase change materials, demonstrating that new areas of technological development for phase change materials are perhaps in some ways even more exciting than existing ones

Reconfigurable nanophotonic devices using phase-change materials

This is the final version of the article. Available from E\PCOS via the URL in this record.Nanophotonic integrated circuits enable realizing functional optical devices using efficient design and fabrication routines. Their inherent stability and scalability makes them attractive for applications where optical signal processing is combined with coupling to external light stimuli. A majority of nanophotonic devices is, however, based on passive materials, which do not provide low-power tuning options or knobs for reconfigurability. We address this shortcoming by combining passive silicon nitride photonic devices with tunable phase-change materials [1]. Such a platform allows realizing both on-chip optical data storage [2] and active photonic components. Implementing on-chip photonic memories has been pursued for a long time, in particular for fabricating memory devices which are able to retain their state after the storage process. Photonic data storage would dramatically improve performance in existing computing architectures by reducing the latencies associated with electrical memories and potentially eliminating optoelectronic conversions. Furthermore, multi-level photonic memories with random access would allow for leveraging even greater computational capability. Thus far, photonic memories have been predominantly volatile, meaning that their state is lost once the input power is removed. We exploit hybrid photonic-phasechange materials to implement robust, non-volatile, all-photonic memories. By using optical near-field coupling within on-chip waveguides, we realize bit storage of up to eight levels in a single device that readily switches between intermediate states. We show that individual memory elements can be addressed using a wavelength multiplexing scheme. Such multi-level, multi-bit devices provide a pathway towards eliminating the von Neumann bottleneck and portend a new paradigm in all-photonic memory and non-conventional computing. We further show that such devices can be operated with short optical pulses, both for write and read operations

On-chip photonic synapse

This is the final version of the article. Available from the American Association for the Advancement of Science via the DOI in this record.The search for new "neuromorphic computing" architectures that mimic the brain's approach to simultaneous processing and storage of information is intense. Because, in real brains, neuronal synapses outnumber neurons by many orders of magnitude, the realization of hardware devices mimicking the functionality of a synapse is a first and essential step in such a search. We report the development of such a hardware synapse, implemented entirely in the optical domain via a photonic integrated-circuit approach. Using purely optical means brings the benefits of ultrafast operation speed, virtually unlimited bandwidth, and no electrical interconnect power losses. Our synapse uses phase-change materials combined with integrated silicon nitride waveguides. Crucially, we can randomly set the synaptic weight simply by varying the number of optical pulses sent down the waveguide, delivering an incredibly simple yet powerful approach that heralds systems with a continuously variable synaptic plasticity resembling the true analog nature of biological synapses.This research was supported via the Engineering and Physical Sciences Research Council Manufacturing Fellowship EP/J018694/1, the Wearable and Flexible Technologies (WAFT) collaboration (EP/M015173/1), and the Chalcogenide Advanced Manufacturing Partnership (EP/M015130/1)