Generalized Teleportation Protocol

A generalized teleportation protocol (GTP) for N qubits is presented, where the teleportation channels are non-maximally entangled and all the free parameters of the protocol are considered: Alice's measurement basis, her sets of acceptable results, and Bob's unitary operations. The full range of Fidelity (F) of the teleported state and the Probability of Success (P_{suc}) to obtain a given fidelity are achieved by changing these free parameters. A channel efficiency bound is found, where one can determine how to divide it between F and P_{suc}. A one qubit formulation is presented and then expanded to N qubits. A proposed experimental setup that implements the GTP is given using linear optics.Comment: 4 pages, 2 figures, RevTex4, published versio

Universal Dephasing Control During Quantum Computation

Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in quantum systems and the corruption of quantum information. We present a universal dynamical control approach to combat dephasing during all stages of quantum computation, namely, storage, single- and two-qubit operators. We show that (a) tailoring multi-frequency gate pulses to the dephasing dynamics can increase fidelity; (b) cross-dephasing, introduced by entanglement, can be eliminated by appropriate control fields; (c) counter-intuitively and contrary to previous schemes, one can increase the gate duration, while simultaneously increasing the total gate fidelity.Comment: 4 pages,3 figure

Optimal Dynamical Decoherence Control of a Qubit

A theory of dynamical control by modulation for optimal decoherence reduction is developed. It is based on the non-Markovian Euler-Lagrange equation for the energy-constrained field that minimizes the average dephasing rate of a qubit for any given dephasing spectrum.Comment: 6 pages, including 2 figures and an appendi

Non-Markovian control of qubit thermodynamics by frequent quantum measurements

We explore the effects of frequent, impulsive quantum nondemolition measurements of the energy of two-level systems (TLS), alias qubits, in contact with a thermal bath. The resulting entropy and temperature of both the system and the bath are found to be completely determined by the measurement rate, and unrelated to what is expected by standard thermodynamical rules that hold for Markovian baths. These anomalies allow for very fast control of heating, cooling and state-purification (entropy reduction) of qubits, much sooner than their thermal equilibration time.Comment: 8 pages, 9 figure

Universal dynamical decoherence control of noisy single-and multi-qubit systems

In this article we develop, step by step, the framework for universal dynamical control of two-level systems (TLS) or qubits experiencing amplitude- or phase-noise (AN or PN) due to coupling to a thermal bath. A comprehensive arsenal of modulation schemes is introduced and applied to either AN or PN, resulting in completely analogous formulae for the decoherence rates, thus underscoring the unified nature of this universal formalism. We then address the extension of this formalism to multipartite decoherence control, where symmetries are exploited to overcome decoherence.Comment: 28 pages, 4 figure