Increasing and decreasing entanglement characteristics for continuous variables by a local photon subtraction

We investigate how the entanglement characteristics of a non-Gaussian entangled state are increased or decreased by a local photon subtraction operation. The non-Gaussian entangled state is generated by injecting a single-mode non-Gaussian state and a vacuum state into a 50:50 beam splitter. We consider a photon-added coherent state and an odd coherent state as a single-mode non-Gaussian state. In the regime of small amplitude, we show that the performance of quantum teleportation and the second-order Einstein-Podolsky- Rosen-type correlation can both be enhanced, whereas the degree of entanglement decreases, for the output state when a local photon subtraction operation is applied to the non-Gaussian entangled state. The counterintuitive effect is more prominent in the limit of nearly zero amplitude.Comment: Published version, 7 pages, 3 figure

Quantum phase estimation using path-symmetric entangled states

We study the sensitivity of phase estimation using a generic class of path-symmetric entangled states $|\varphi\rangle|0\rangle+|0\rangle|\varphi\rangle$, where an arbitrary state $|\varphi\rangle$ occupies one of two modes in quantum superposition. This class of states includes the previously considered states, i.e. $NOON$ states and entangled coherent states, as special cases. With its generalization, we identify the practical limit of phase estimation under energy constraint that is characterized by the photon statistics of the component state $|\varphi\rangle$. We first show that quantum Cramer-Rao bound (QCRB) can be lowered with super-Poissonianity of the state $|\varphi\rangle$. By introducing a component state of the form $|\varphi\rangle=\sqrt{q}|1\rangle+\sqrt{1-q}|N\rangle$, we particularly show that an arbitrarily small QCRB can be achieved even with a finite energy in an ideal situation. For practical measurement schemes, we consider a parity measurement and a full photon-counting method to obtain phase-sensitivity. Without photon loss, the latter scheme employing any path-symmetric states $|\varphi\rangle|0\rangle+|0\rangle|\varphi\rangle$ achieves the QCRB over the entire range $[0,2\pi]$ of unknown phase shift $\phi$ whereas the former does so in a certain confined range of $\phi$. We find that the case of $|\varphi\rangle=\sqrt{q}|1\rangle+\sqrt{1-q}|N\rangle$ provides the most robust resource against loss among the considered entangled states over the whole range of input energy. Finally we also propose experimental schemes to generate these path-symmetric entangled states.Comment: 10 pages, 5 figures, published versio

Influence of reduced water availability on Pseudomonas putida unsaturated biofilms and the role of alginate in desiccation tolerance

Biofilms are aggregates of cells adhering to surfaces embedded in a matrix of extracellular polymeric substances of their own making. Microbial water availability in many terrestrial habitats is one of the most important factors influencing unsaturated biofilm development and biofilm cell survival and death. In general, Pseudomonas putida strain mt-2 unsaturated biofilm formation proceeds through three distinct developmental phases, culminating in the formation of a microcolony. The form and severity of reduced water availability alters cell morphology. The dehydration treatments resulted in biofilms comprised of smaller cells but they were taller and more porous, and had a thicker exopolysaccharide (EPS) layer at the air interface. In the osmotic stress treatments, cell filamentation occurred more frequently in the presence of high concentrations of ionic, but not non-ionic, solutes and these filamented cells drastically altered biofilm Architecture;P. putida produced more EPS in response to dehydration stress, but not thermodynamically equivalent osmotic stress. Carbohydrate composition analysis showed that alginate was a component of unsaturated biofilm EPS only in the presence of dehydration stress. The absence of alginate altered biofilm architecture in that biofilms were shorter, covered more surface area, and were less porous than when alginate was present. By measuring intracellular water potential changes and monitoring fatty acid alterations during dehydration stress, we demonstrated that alginate slows the rate of cellular dehydration. Alginate production also contributed to the ability of cells to survive a severe desiccation stress. These results suggest that an important consequence of cellular dehydration is alginate production, which contributes to the fitness of P. putida in water-limited environments.;Reduced water availability influenced the temporal and spatial localization of dead cells within unsaturated biofilms. Dead cells were organized in arrays of various lengths one cell width. In general, more dead cells were localized in the lower layers, while active, growing cells were localized primarily in the upper layers.;Taken together, reduction of water availability influences biofilm architecture, EPS production, and cell death patterns, which all reflect a status of adaptation of P. putida to dehydration stress. This study provides new insights into microbial dehydration physiology