Complementarity + Back-reaction is enough

We investigate a recent development of the black hole information problem, in which a practical paradox has been formulated to show that complementarity is insufficient. A crucial ingredient in this practical paradox is to distill information from the early Hawking radiation within the past lightcone of the black hole. By causality this action can back-react on the black hole. Taking this back-reaction into account, the paradox could be resolved without invoking any new physics beyond complementarity. This resolution requires a certain constraint on the S-matrix to be satisfied. Further insights into the S-matrix could potentially be obtained by effective-field-theory computations of the back-reaction on the nice slice.Comment: v2, 21 pages, 4 figure

Search for and study of extremely metal-deficient galaxies

We summarize the progress in identifying and observational study of extremely metal-deficient (XMD) gas-rich galaxies (BCGs, dIr and LSBDs). Due to volume limitations only following issues are addressed: sample creation, some statistical data, Colour-Magnitude Diagrams (CMD) and ages, the case of SBS 0335--052 system, and probable evolution paths of various XMD objects.Comment: 4 pages, 3 figures. To appear in the proceedings of Euroconference "The evolution of galaxies. III. From simple approaches to self-consistent models" Kiel, Germany, July 200

Readout methods and devices for Josephson-junction-based solid-state qubits

We discuss the current situation concerning measurement and readout of Josephson-junction based qubits. In particular we focus attention of dispersive low-dissipation techniques involving reflection of radiation from an oscillator circuit coupled to a qubit, allowing single-shot determination of the state of the qubit. In particular we develop a formalism describing a charge qubit read out by measuring its effective (quantum) capacitance. To exemplify, we also give explicit formulas for the readout time.Comment: 20 pages, 7 figures. To be published in J. Phys.: Condensed Matter, 18 (2006) Special issue: Quantum computin

Quantum Nonlocality without Entanglement

We exhibit an orthogonal set of product states of two three-state particles that nevertheless cannot be reliably distinguished by a pair of separated observers ignorant of which of the states has been presented to them, even if the observers are allowed any sequence of local operations and classical communication between the separate observers. It is proved that there is a finite gap between the mutual information obtainable by a joint measurement on these states and a measurement in which only local actions are permitted. This result implies the existence of separable superoperators that cannot be implemented locally. A set of states are found involving three two-state particles which also appear to be nonmeasurable locally. These and other multipartite states are classified according to the entropy and entanglement costs of preparing and measuring them by local operations.Comment: 27 pages, Latex, 6 ps figures. To be submitted to Phys. Rev. A. Version 2: 30 pages, many small revisions and extensions, author added. Version 3: Proof in Appendix D corrected, many small changes; final version for Phys. Rev. A Version 4: Report of Popescu conjecture modifie

An Investigation of AdS2_2 Backreaction and Holography

We investigate a dilaton gravity model in AdS$_2$ proposed by Almheiri and Polchinski and develop a 1d effective description in terms of a dynamical boundary time with a Schwarzian derivative action. We show that the effective model is equivalent to a 1d version of Liouville theory, and investigate its dynamics and symmetries via a standard canonical framework. We include the coupling to arbitrary conformal matter and analyze the effective action in the presence of possible sources. We compute commutators of local operators at large time separation, and match the result with the time shift due to a gravitational shockwave interaction. We study a black hole evaporation process and comment on the role of entropy in this model.Comment: 32 pages, 6 figures, v3: typos corrected and references added, matches published versio

Deterministic quantum teleportation between distant atomic objects

Quantum teleportation is a key ingredient of quantum networks and a building block for quantum computation. Teleportation between distant material objects using light as the quantum information carrier has been a particularly exciting goal. Here we demonstrate a new element of the quantum teleportation landscape, the deterministic continuous variable (cv) teleportation between distant material objects. The objects are macroscopic atomic ensembles at room temperature. Entanglement required for teleportation is distributed by light propagating from one ensemble to the other. Quantum states encoded in a collective spin state of one ensemble are teleported onto another ensemble using this entanglement and homodyne measurements on light. By implementing process tomography, we demonstrate that the experimental fidelity of the quantum teleportation is higher than that achievable by any classical process. Furthermore, we demonstrate the benefits of deterministic teleportation by teleporting a dynamically changing sequence of spin states from one distant object onto another