A case study in decompounding for Bengali information retrieval

Decompounding has been found to improve information retrieval (IR) effectiveness for compounding languages such as Dutch, German, or Finnish. No previous studies, however, exist on the effect of decomposition of compounds in IR for Indian languages. In this case study, we investigate the effect of decompounding for Bengali, a highly agglutinative Indian language. Some unique characteristics of Bengali compounding are: i) only one constituent may be a valid word in contrast to the stricter requirement of both being so; and ii) the first character of the right constituent can be modified by the rules of sandhi in contrast to simple concatenation. While the standard approach of decompounding based on maximization of the total frequency of the constituents formed by candidate split positions has proven beneficial for European languages, our reported experiments in this paper show that such a standard approach does not work particularly well for Bengali IR. As a solution, we firstly propose a more relaxed decompounding where a compound word can be decomposed into only one constituent if the other constituent is not a valid word, and secondly we perform selective decompounding by employing a co-occurrence threshold to ensure that the constituent often co-occurs with the compound word, which in this case is representative of how related are the constituents with the compound. We perform experiments on Bengali ad-hoc IR collections from FIRE 2008 to 2012. Our experiments show that both the relaxed decomposition and the co-occurrence-based constituent selection proves more effective than the standard frequency-based decomposition. improving MAP up to 2:72% and recall up to 1:8%

Cryogenic setup for trapped ion quantum computing

We report on the design of a cryogenic setup for trapped ion quantum computing containing a segmented surface electrode trap. The heat shield of our cryostat is designed to attenuate alternating magnetic field noise, resulting in 120~dB reduction of 50~Hz noise along the magnetic field axis. We combine this efficient magnetic shielding with high optical access required for single ion addressing as well as for efficient state detection by placing two lenses each with numerical aperture 0.23 inside the inner heat shield. The cryostat design incorporates vibration isolation to avoid decoherence of optical qubits due to the motion of the cryostat. We measure vibrations of the cryostat of less than $\pm$20~nm over 2~s. In addition to the cryogenic apparatus, we describe the setup required for an operation with $^{\mathrm{40}}$Ca$^{\mathrm{+}}$ and $^{\mathrm{88}}$Sr$^{\mathrm{+}}$ ions. The instability of the laser manipulating the optical qubits in $^{\mathrm{40}}$Ca$^{\mathrm{+}}$ is characterized yielding a minimum of its Allan deviation of 2.4$\cdot$10$^{\mathrm{-15}}$ at 0.33~s. To evaluate the performance of the apparatus, we trapped $^{\mathrm{40}}$Ca$^{\mathrm{+}}$ ions, obtaining a heating rate of 2.14(16)~phonons/s and a Gaussian decay of the Ramsey contrast with a 1/e-time of 18.2(8)~ms

High-fidelity local addressing of trapped ions and atoms by composite sequences of laser pulses

A vital requirement for a quantum computer is the ability to locally address, with high fidelity, any of its qubits without affecting their neighbors. We propose an addressing method using composite sequences of laser pulses, which reduces dramatically the addressing error in a lattice of closely spaced atoms or ions, and at the same time significantly enhances the robustness of qubit manipulations. To this end, we design novel high-fidelity composite pulses for the most important single-qubit operations. In principle, this method allows one to beat the diffraction limit, for only atoms situated in a small spatial region around the center of the laser beam are excited, well within the laser beam waist.Comment: Optics Letters Vol. 36, No. 7 (2011