A non-Markovian optical signature for detecting entanglement in coupled excitonic qubits

We identify an optical signature for detecting entanglement in experimental nanostructure systems comprising coupled excitonic qubits. This signature owes its strength to non-Markovian dynamical effects in the second-order temporal coherence function of the emitted radiation. We calculate autocorrelation and cross-correlation functions for both selective and collective light excitation, and prove that the coherence properties of the emitted light do indeed carry information about the entanglement of the initial multi-qubit state. We also show that this signature can survive in the presence of a noisy environment.Comment: 4 pages, 4 color figures. Minor changes. Accepted version to be published in Europhysics Letter

Ultrafast optical signature of quantum superpositions in a nanostructure

We propose an unambiguous signature for detecting quantum superposition states in a nanostructure, based on current ultrafast spectroscopy techniques. The reliable generation of such superposition states via Hadamard-like quantum gates is crucial for implementing solid-state based quantum information schemes. The signature originates from a remarkably strong photon antibunching effect which is enhanced by non-Markovian dynamics.Comment: 4 pages, 2 figures. Published in Phys. Rev. B (Rapid Communications

Corporate ethical policies: evidence from large firms in Chile

This study explores the current status of corporate ethical policies in the large-size firms currently operating in Chile and focus on the edition of formal documents on corporate ethics by means of a survey sent to the companies whose manning table exceeds 350 employees (460 firms), using for this selection the 2005 Directorio ITV de Empresas en Chile (ITV Directory of Corporations in Chile). The results obtained from the 116 responses received reveal that almost 60% of the firms possess ethics corporate documents; that in general there is consensus about the need to bear in mind the ethical conduct in the personnel selection, promotion and bonuses; and that generally a greater proportion of foreign firms have documents on ethics, as compared with the domestic firms. Likewise, a statistical verification was performed –whose results are only extrapolated to the large-size firms– on the correlation between possession of formal ethics documents and performance (measured as the value of 2005 sales), which had positive results and was statistically significant; at the same time, evidence was found, although somewhat weaker, to support the hypothesis of statistically positive correlation between such documents possession and the number of employees.Corporate ethical documents; Business ethics policy; Codes of conduct; Chile

A robust one-step catalytic machine for high fidelity anti-cloning and W-state generation in a multi-qubit system

We propose a physically realizable machine which can either generate multiparticle W-like states, or implement high fidelity $1 \to M$ ($M=1,2,... \infty$) anti-cloning of an arbitrary qubit state, in a single step. Moreover this universal machine acts as a catalyst in that it is unchanged after either procedure, effectively resetting itself for its next operation. It also possesses an inherent {\em immunity} to decoherence. Most importantly in terms of practical multi-party quantum communication, the machine's robustness in the presence of decoherence actually {\em increases} as the number of qubits $M$ increases.Comment: 4 pages, 2 figure

Ultrafast deterministic generation of entanglement in a time-dependent asymmetric two-qubit-cavity system

We present an efficient scheme for the controlled generation of pure two-qubit states possessing {\em any} desired degree of entanglement and a {\em prescribed} symmetry in two cavity QED based systems, namely, cold trapped ions and flying atoms. This is achieved via on-resonance ion/atom-cavity couplings which are time-dependent and asymmetric, leading to a trapping vacuum state condition which does not arise for identical couplings. A duality in the role of the coupling ratio yields states with a given concurrence but opposing symmetries. The experimental feasibility of the proposed scheme is also discussed.Comment: 4 pages, 4 figure

New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions

We reveal universal dynamical scaling behavior across adiabatic quantum phase transitions (QPTs) in networks ranging from traditional spatial systems (Ising model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our findings, which lie beyond traditional critical exponent analysis and adiabatic perturbation approximations, are applicable even where excitations have not yet stabilized and hence provide a time-resolved understanding of QPTs encompassing a wide range of adiabatic regimes. We show explicitly that even though two systems may traditionally belong to the same universality class, they can have very different adiabatic evolutions. This implies more stringent conditions need to be imposed than at present, both for quantum simulations where one system is used to simulate the other, and for adiabatic quantum computing schemes.Comment: 5 pages, 3 figures, plus supplementary material (6 pages, 1 figure

Large dynamic light-matter entanglement from driving neither too fast nor too slow

A significant problem facing next-generation quantum technologies is how to generate and manipulate macroscopic entanglement in light and matter systems. Here we report a new regime of dynamical light-matter behavior in which a giant, system-wide entanglement is generated by varying the light-matter coupling at \emph{intermediate} velocities. This enhancement is far larger and broader-ranged than that occurring near the quantum phase transition of the same model under adiabatic conditions. By appropriate choices of the coupling within this intermediate regime, the enhanced entanglement can be made to spread system-wide or to reside in each subsystem separately.Comment: 7 pages, 7 figure

Robust quantum correlations in out-of-equilibrium matter-light systems

High precision macroscopic quantum control in interacting light-matter systems remains a significant goal toward novel information processing and ultra-precise metrology. We show that the out-of-equilibrium behavior of a paradigmatic light-matter system (Dicke model) reveals two successive stages of enhanced quantum correlations beyond the traditional schemes of near-adiabatic and sudden quenches. The first stage features magnification of matter-only and light-only entanglement and squeezing due to effective non-linear self-interactions. The second stage results from a highly entangled light-matter state, with enhanced superradiance and signatures of chaotic and highly quantum states. We show that these new effects scale up consistently with matter system size, and are reliable even in dissipative environments.Comment: 14 pages, 6 figure