5,141 research outputs found
Two hybrid ARQ error control schemes for near earth satellite communications
Two hybrid automatic repeat request (ARQ) error control schemes are proposed for NASA near earth satellite communications. Both schemes are adaptive in nature, and employ cascaded codes to achieve both high reliability and throughput efficiency for high data rate file transfer
Scalable Quantum Networks based on Few-Qubit Registers
We describe and analyze a hybrid approach to scalable quantum computation
based on an optically connected network of few-qubit quantum registers. We show
that probabilistically connected five-qubit quantum registers suffice for
deterministic, fault-tolerant quantum computation even when state preparation,
measurement, and entanglement generation all have substantial errors. We
discuss requirements for achieving fault-tolerant operation for two specific
implementations of our approach.Comment: 4 pages, 3 figures (new figures 1 and 3
Exploring More-Coherent Quantum Annealing
In the quest to reboot computing, quantum annealing (QA) is an interesting
candidate for a new capability. While it has not demonstrated an advantage over
classical computing on a real-world application, many important regions of the
QA design space have yet to be explored. In IARPA's Quantum Enhanced
Optimization (QEO) program, we have opened some new lines of inquiry to get to
the heart of QA, and are designing testbed superconducting circuits and
conducting key experiments. In this paper, we discuss recent experimental
progress related to one of the key design dimensions: qubit coherence. Using
MIT Lincoln Laboratory's qubit fabrication process and extending recent
progress in flux qubits, we are implementing and measuring QA-capable flux
qubits. Achieving high coherence in a QA context presents significant new
engineering challenges. We report on techniques and preliminary measurement
results addressing two of the challenges: crosstalk calibration and qubit
readout. This groundwork enables exploration of other promising features and
provides a path to understanding the physics and the viability of quantum
annealing as a computing resource.Comment: 7 pages, 3 figures. Accepted by the 2018 IEEE International
Conference on Rebooting Computing (ICRC
Achieving the Heisenberg limit in quantum metrology using quantum error correction
Quantum metrology has many important applications in science and technology,
ranging from frequency spectroscopy to gravitational wave detection. Quantum
mechanics imposes a fundamental limit on measurement precision, called the
Heisenberg limit, which can be achieved for noiseless quantum systems, but is
not achievable in general for systems subject to noise. Here we study how
measurement precision can be enhanced through quantum error correction, a
general method for protecting a quantum system from the damaging effects of
noise. We find a necessary and sufficient condition for achieving the
Heisenberg limit using quantum probes subject to Markovian noise, assuming that
noiseless ancilla systems are available, and that fast, accurate quantum
processing can be performed. When the sufficient condition is satisfied, a
quantum error-correcting code can be constructed which suppresses the noise
without obscuring the signal; the optimal code, achieving the best possible
precision, can be found by solving a semidefinite program.Comment: 16 pages, 2 figures, see also arXiv:1704.0628
Automatic-repeat-request error control schemes
Error detection incorporated with automatic-repeat-request (ARQ) is widely used for error control in data communication systems. This method of error control is simple and provides high system reliability. If a properly chosen code is used for error detection, virtually error-free data transmission can be attained. Various types of ARQ and hybrid ARQ schemes, and error detection using linear block codes are surveyed
Phase gate and readout with an atom/molecule hybrid platform
We suggest a combined atomic/molecular system for quantum computation, which
takes advantage of highly developed techniques to control atoms and recent
experimental progress in manipulation of ultracold molecules. We show that two
atoms of different species in a given site, {\it e.g.}, in an optical lattice,
could be used for qubit encoding, initialization and readout, with one atom
carrying the qubit, the other enabling a gate. In particular, we describe how a
two-qubit phase gate can be realized by transferring a pair of atoms into the
ground rovibrational state of a polar molecule with a large dipole moment, and
allowing two molecules to interact via their dipole-dipole interaction. We also
discuss how the reverse process of coherently transferring a molecule into a
pair of atoms could be used as a readout tool for molecular quantum computers
Nonlinear feedback control of multiple robot arms
Multiple coordinated robot arms are modeled by considering the arms: (1) as closed kinematic chains, and (2) as a force constrained mechanical system working on the same object simultaneously. In both formulations a new dynamic control method is discussed. It is based on a feedback linearization and simultaneous output decoupling technique. Applying a nonlinear feedback and a nonlinear coordinate transformation, the complicated model of the multiple robot arms in either formulation is converted into a linear and output decoupled system. The linear system control theory and optimal control theory are used to design robust controllers in the task space. The first formulation has the advantage of automatically handling the coordination and load distribution among the robot arms. In the second formulation, by choosing a general output equation, researchers can superimpose the position and velocity error feedback with the force-torque error feedback in the task space simultaneously
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