Quantum Information Processing with Continuous Variables and Atomic Ensembles

Abstract

This thesis presents three different results in quantum information theory. The first result addresses the theoretical foundations of quantum metrology. The Heisenberg limit considered as the ultimate limit in quantum metrology sets a lower bound on how precisely a physical quantity can be measured given a certain amount of resources in any possible measurement. Recently, however, several measurement procedures have been proposed in which the Heisenberg limit seemed to be surpassed. This led to an extensive debate over the question how the sensitivity scales with the physical resources and the computational resources that are used in estimation procedures. Here, we reconcile the physical definition of the relevant resources with the information-theoretical scaling in terms of the query complexity of a quantum network. This leads to a novel and ultimate Heisenberg limit that applies to all conceivable measurement procedures. The second result reveals a close relationship between quantum metrology and the Deutsch-Jozsa algorithm over continuous-variable quantum systems. Here, we develop a general procedure, characterized by two parameters, that unifies parameter estimation and the Deutsch-Jozsa algorithm. The procedure estimates a value of an unknown parameter with Heisenberg-limited precision or solves the Deutsch-Jozsa problem in a single run without the use of any entanglement. The third result illustrates how physical principles that govern interaction of light and matter can be efficiently employed to create a computational resource for a (one-way) quantum computer. More specifically, we demonstrate theoretically a scheme based on atomic ensembles and the dipole blockade mechanism for generation of the so-called cluster states in a single step. This procedure is significantly more efficient than any known robust probabilistic entangling operation.

PhD Thesis, University of Sheffield, UK (January 2011), 142 pages, 21 figures

References in corpus (36)

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• Single-shot read-out of an individual electron spin in a quantum dot
• Measurement-based quantum computation
• Multi-party entanglement in graph states
• Topological fault-tolerance in cluster state quantum computation
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• Generalized Limits for Single-Parameter Quantum Estimation
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• Long-range interactions and entanglement of slow single-photon pulses
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• Superconducting Qubits: A Short Review
• High purity bright single photon source
• Thresholds for topological codes in the presence of loss
• Spatially resolved observation of dipole-dipole interaction between Rydberg atoms
• Brokered Graph State Quantum Computing
• Quantum information processing with single photons and atomic ensembles in microwave coplanar waveguide resonators
• Multi-path entanglement of two photons
• On experimental procedures for entanglement verification
• Interfacing light and single atoms with a lens
• All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption
• Collisional decoherence during writing and reading quantum states
• Communication Links for Distributed Quantum Computation
• Entanglement is not a critical resource for quantum metrology
• Dynamics of Low-Density Ultracold Rydberg Gases
• High-efficiency cluster-state generation with atomic ensembles via the dipole-blockade mechanism
• Realization of Coherent Optically Dense Media via Buffer-Gas Cooling
• Cluster state preparation using gates operating at arbitrary success probabilities
• How much of one-way computation is just thermodynamics?
• Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
• Topological stability of stored optical vortices