Quantum phase estimation with lossy interferometers

We give a detailed discussion of optimal quantum states for optical two-mode interferometry in the presence of photon losses. We derive analytical formulae for the precision of phase estimation obtainable using quantum states of light with a definite photon number and prove that maximization of the precision is a convex optimization problem. The corresponding optimal precision, i.e. the lowest possible uncertainty, is shown to beat the standard quantum limit thus outperforming classical interferometry. Furthermore, we discuss more general inputs: states with indefinite photon number and states with photons distributed between distinguishable time bins. We prove that neither of these is helpful in improving phase estimation precision.Comment: 12 pages, 5 figure

Phonon Life-times from first principles self consistent lattice dynamics

Phonon lifetime calculations from first principles usually rely on time consuming molecular dynamics calculations, or density functional perturbation theory (DFPT) where the zero temperature crystal structure is assumed to be dynamically stable. Here a new and effective method for calculating phonon lifetimes from first principles is presented, not limited to crystal structures stable at 0 K, and potentially much more effective than most corresponding molecular dynamics calculations. The method is based on the recently developed self consistent lattice dynamical method and is here tested by calculating the bcc phase phonon lifetimes of Li, Na, Ti and Zr, as representative examples.Comment: 4 pages, 4 figur

Quantum frequency estimation with trapped ions and atoms

We discuss strategies for quantum enhanced estimation of atomic transition frequencies with ions stored in Paul traps or neutral atoms trapped in optical lattices. We show that only marginal quantum improvements can be achieved using standard Ramsey interferometry in the presence of collective dephasing, which is the major source of noise in relevant experimental setups. We therefore analyze methods based on decoherence free subspaces and prove that quantum enhancement can readily be achieved even in the case of significantly imperfect state preparation and faulty detections.Comment: 5 pages + 6 pages appendices; published versio

DETECTING PANIC POTENTIAL IN SOCIAL MEDIA TWEETS

A high degree of real-time interconnectedness can aid information transmission, particularly in disaster situations. However, it can have substantial negative consequences when information is emotionally laden and transmits these emotions, particularly the emotion of panic, to the individual across social media in an already grave situation. Prior research has shown that information laden with emotion spreads through social network faster than otherwise. Hence, we highlight the need to understand and curtail potentially panic-causing information, without compromising on good quality information from being available for effective crisis communication and management. With this research, we present the necessity of detecting the panic potential of social media messages, and aim to address two research questions: What are the features, and metrics necessary, to compute and evaluate the panic potential of a social media message (respectively)? Our planned analysis takes the case of the Munich shooting incident, 2016, based on user tweets immediately after the incident. Different features and evaluation metrics are proposed and discussed. The work aims to detect panic potential of messages in social media networks during disasters

Poxviral/Retroviral Chimeric Vectors Allow Cytoplasmic Production of Transducing Defective Retroviral Particles

AbstractDefective vaccinia viruses were constructed that express functional Moloney murine leukemia virus-based vector genomes, giving rise to substantial titers of transduction-competent retrovirus particles after infection of a retroviral packaging cell line. For this purpose, the proviral retrovirus genome, engineered into the vaccinia virus mutant, was subjected to several modifications, including the replacement of retroviral promoter sequences by vaccinia virus sequences and the precise fusion of the transcription stop signal downstream of and the removal of such signals within the transcription unit, allowing cytoplasmic transcription of distinct full-length retroviral transcripts. Vaccinia-mediated expression of retroviral vector particles could be observed as early as 3 h postinfection and resulted in stable transduction of NIH/3T3 target cells at higher titers than the control performed by conventional plasmid transfections. Thus at least part of the vaccinia life cycle and retroviral assembly can occur concomitantly. Due to the favorable properties of vaccinia vectors, including high coding capacity, stability, and wide host range, defective vaccinia viral/retroviral chimeric vectors are promising tools for gene therapy applications

Dynamics of a Quantum Phase Transition

We present two approaches to the dynamics of a quench-induced phase transition in quantum Ising model. The first one retraces steps of the standard approach to thermodynamic second order phase transitions in the quantum setting. The second one is purely quantum, based on the Landau-Zener formula for transition probabilities in avoided level crossings. We show that the two approaches yield compatible results for the scaling of the defect density with the quench rate. We exhibit similarities between them, and comment on the insights they give into dynamics of quantum phase transitions.Comment: 4 pages, 3 figures. Replaced by revised versio

Quantum computations with atoms in optical lattices: marker qubits and molecular interactions

We develop a scheme for quantum computation with neutral atoms, based on the concept of "marker" atoms, i.e., auxiliary atoms that can be efficiently transported in state-independent periodic external traps to operate quantum gates between physically distant qubits. This allows for relaxing a number of experimental constraints for quantum computation with neutral atoms in microscopic potential, including single-atom laser addressability. We discuss the advantages of this approach in a concrete physical scenario involving molecular interactions.Comment: 15 pages, 14 figure