1,771 research outputs found
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
- …