22 research outputs found

    Optical nonlinearities near single photon level with a quantum dot coupled to a photonic crystal cavity

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    Over the last decade, exponential increase of information bandwidth over the internet and other communication media has increased the total power consumed by the devices associated with information exchange. With ever increasing number of users, and packing of a higher number of devices onto a chip, there is a great need for reduction in not only the power consumption of the devices but also the costs associated with information transfer. Currently, the benchmark in the energy consumption per logic operation is at femtojoule level and is set by the CMOS industry. However, optical devices based on single photon emitters coupled to a microcavity have the potential to reduce the optical power dissipation down to attojoule levels wherein only few 10s of photons are consumed for a logic operation. This work presents our theoretical and experimental efforts towards realization of all optical device based on the enhanced nonlinearities of a single photon emitter in a photonic crystal cavity. We show that a single quantum dot coupled to a photonic crystal cavity can be used to route an incoming optical beam with optical power dissipation of 14 attojoules, corresponding to only 65 photons. This value is well below the operational level for current CMOS devices indicating the potential for chip based optical transistors for reduction in energy consumption. The single photon emitters that we use to create the nonlinearity are the quantum dots, which are semiconductor nanostructures that exhibit a discrete energy spectrum. The interaction of the quantum dot, with light confined inside a photonic crystal cavity, results in strong atom-photon interactions which can be used for ultra-low power all optical switching. The strong interactions between a quantum dot and photonic crystal cavity can be further utilized to realize quantum computation schemes on a chip. I also describe techniques for integrating this transistor into an optical circuit, and discuss methods for post fabrication tuning to make reconfigurable active photonic devices that implement optical data processing at low light levels

    Generating entanglement between quantum dots with different resonant frequencies based on Dipole Induced Transparency

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    We describe a method for generating entanglement between two spatially separated dipoles coupled to optical micro-cavities. The protocol works even when the dipoles have different resonant frequencies and radiative lifetimes. This method is particularly important for solid-state emitters, such as quantum dots, which suffer from large inhomogeneous broadening. We show that high fidelities can be obtained over a large dipole detuning range without significant loss of efficiency. We analyze the impact of higher order photon number states and cavity resonance mismatch on the performance of the protocol

    Application of Ultrasonic Technique for Measurement of Instantaneous Burn Rate of Solid Propellants .

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    The ultrasonic pulse-echo technique has been applied for the measurement of instantaneous burnrate of aluminised composite solid propellants. The tests have been carried out on end-burning 30 mmthick propellant specimens at nearly constant pressure of about 1.9 MPa. Necessary software forpost-test data processing and instantaneous burn rate computations have been developed. The burnrates measured by the ultrasonic technique have been compared with those obtained from ballisticevaluation motor tests on propellant from the same mix. An accuracy of about +- 1 per cent ininstantaneous burn rate measurements and reproducibility of results have been demonstrated byapplying ultrasonic technique

    Munchausen Syndrome Masquerading as Bleeding Disorder in a Group of Pediatric Patients

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    This short communication is about Munchausen's syndrome in a group of pediatric patients and co morbid Munchausen's syndrome by proxy. A 7-year-old girl presented with spontaneous bleeding from forehead, eyes and scalp. The girl was investigated thoroughly by pediatricians at a tertiary care hospital in western India for all possible bleeding disorders, but there was no conclusive diagnosis. After two days, cases with similar complaints were reported among children residing in the same locality and with similar socioeconomic background. All of them were investigated in detail for possible causes of bleeding but nothing came out. There was a media reporting of the cases as a mysterious bleeding disorder. At this point of time, an expert opinion from the psychiatrist was demanded. Covert video surveillance and series of interviews revealed Munchausen's syndrome and possible Munchausen's syndrome by proxy. An in-depth literature review with special reference to Munchausen's syndrome was carried out to come to a final conclusive diagnosis

    LDPC block and convolutional codes based on circulant matrices

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    A class of algebraically structured quasi-cyclic (QC) low-density parity-check (LDPC) codes and their convolutional counterparts is presented. The QC codes are described by sparse parity-check matrices comprised of blocks of circulant matrices. The sparse parity-check representation allows for practical graph-based iterative message-passing decoding. Based on the algebraic structure, bounds on the girth and minimum distance of the codes are found, and several possible encoding techniques are described. The performance of the QC LDPC block codes compares favorably with that of randomly constructed LDPC codes for short to moderate block lengths. The performance of the LDPC convolutional codes is superior to that of the QC codes on which they are based; this performance is the limiting performance obtained by increasing the circulant size of the base QC code. Finally, a continuous decoding procedure for the LDPC convolutional codes is described