Search via quantum walks with intermediate measurements

A modification of Tulsi's quantum search algorithm with intermediate measurements of the control qubit is presented. In order to analyze the effect of measurements in quantum searches, a different choice of the angular parameter is used. The study is performed for several values of time lapses between measurements, finding close relationships between probabilities and correlations (mutual information and cumulative correlation measure). The order of this modified algorithm is estimated, showing that for some time lapses the performance is improved, and becomes of order O(N) (classical brute-force search) when measurements are taken in every step. The results provide a possible way to analyze improvements to other quantum algorithms using one, or more, control qubits

Understanding Quantum Technologies 2022

Understanding Quantum Technologies 2022 is a creative-commons ebook that provides a unique 360 degrees overview of quantum technologies from science and technology to geopolitical and societal issues. It covers quantum physics history, quantum physics 101, gate-based quantum computing, quantum computing engineering (including quantum error corrections and quantum computing energetics), quantum computing hardware (all qubit types, including quantum annealing and quantum simulation paradigms, history, science, research, implementation and vendors), quantum enabling technologies (cryogenics, control electronics, photonics, components fabs, raw materials), quantum computing algorithms, software development tools and use cases, unconventional computing (potential alternatives to quantum and classical computing), quantum telecommunications and cryptography, quantum sensing, quantum technologies around the world, quantum technologies societal impact and even quantum fake sciences. The main audience are computer science engineers, developers and IT specialists as well as quantum scientists and students who want to acquire a global view of how quantum technologies work, and particularly quantum computing. This version is an extensive update to the 2021 edition published in October 2021.Comment: 1132 pages, 920 figures, Letter forma

Bounds on the entanglability of thermal states in liquid-state nuclear magnetic resonance

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 235-243).Theorists have recently shown that the states used in current nuclear magnetic resonance (NMIR) quantum computing experiments are not entangled. Yet it is widely believed that entanglement is a necessary resource in the implementation of quantum algorithms. The apparent contradiction might be resolved by the experimental realization of an entangled NMR state. Designing such an experiment requires us to know whether or not the initial NMR state is entanglable--that is, does there exist a unitary transform that entangles the state? This computational and theoretical thesis explores the entanglability of thermal states in N-[alpha] space where N specifies the number of qubits and [alpha] characterizes the polarization of the thermal state. The thermal state is transformed by the Bell unitary U[sub]b,s and the entanglement of the transformed state is measured by negativity. Here we present numerically generated negativity maps of N-[alpha] space (N [less than or equal to] 12) and explicit negativity formulas for U[sub]b,s-transformed thermal states. We also give a general method that uses the symmetry of a special mixed Bell state family to derive bounds on the entanglement of generic Bell-transformed thermal states. This approach yields analytical bounds on the entanglability of thermal states and gives an upper limit of N [less than or equal to] 20, 054 required to entangle a thermal state under ideal experimental conditions.by Terri M. Yu.M.Eng