Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence 1 . For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death 2,3 . Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing 4 , quantum cryptography 5 , quantum teleportation 6-8 and quantum metrology 9 . Here, we propose and demonstrate a scheme to protect entanglement from decoherence. Our entanglement protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death.One way to cope with decoherence is to make use of entanglement distillation protocols by which a pure maximally entangled state may be obtained from multiple copies of partially decohered states 4,10-14 . Note, however, that it is impossible to obtain an entangled state from copies of fully decohered (that is, separable) states by applying entanglement distillation 15 . Another method to deal with decoherence is to rely on the so-called decoherence-free subspace 16,17 . The decoherence-free subspace, however, requires the interaction Hamiltonian to have an appropriate symmetry, which might not always be present. The quantum Zeno effect may also be used to suppress decoherence 18,19 as well as to generate entanglement 20 under some specific situations.Our scheme for protecting entanglement from decoherence is based on the fact that weak quantum measurement can be reversed. The reversibility of weak quantum measurement was originally discussed in the context of quantum error correction 21 and was demonstrated for a single superconducting qubit and a single photonic qubit [22][23][24] . Recently, it was shown that weak measurement and quantum measurement reversal can effectively suppress amplitude-damping decoherence for a single qubit 25,26 . Here, we experimentally demonstrate a scheme for protecting entanglement from amplitude-damping decoherence using weak measurement and quantum measurement reversal. The scheme can reduce or even completely nullify the effect of decoherence as evidenced by increased concurrence of the two-qubit system.Consider a two-level quantum system (S) whose computational bases are |0 S and |1 S . The environment (E) is initially at |0 E . Amplitude-damping decoherence, in which a particular computational basis state is irreversibly and probabilistically transferred to the other, results from state-dependent coupling of the system qubit to the environment and is described by the following quantum map,where 0 ≤ D ≤ 1 is the magnitude of the decoherence andAmplitude-damping decoherence is highly relevant for many practical qubit systems. For instance, amplitudedamping decoherence is caused by photon loss for the vacuumsingle-photon qubit, by spontaneous decay for the atomic energy level qubit and by zero-temperat...

Taming decoherence is essential in realizing quantum computation and quantum communication. Here we experimentally demonstrate that decoherence due to amplitude damping can be suppressed by exploiting quantum measurement reversal in which a weak measurement and the reversing measurement are introduced before and after the decoherence channel, respectively. We have also investigated the trade-off relation between the degree of decoherence suppression and the channel transmittance.

An actively antagonistic bacterium that could be used as a biocontrol agent against Fusarium solani, which causes root rots with considerable losses in many important crops, was isolated from a ginseng rhizosphere and identified as a strain of Pseudomonas stutzeri. In several biochemical tests with culture filtrates of P. stutzeri YPL-1 and in mutational analyses of antifungal activities of reinforced or defective mutants, we found that the anti-F. solani mechanism of the bacterium may involve a lytic enzyme rather than a toxic substance or antibiotic. P. stutzeri YPL-1 produced extracellular chitinase and laminarinase when grown on different polymers such as chitin, laminarin, or F. solani mycelium. These lytic extracellular enzymes markedly inhibited mycelial growth rather than spore germination and also caused lysis of F. solani mycelia and germ tubes. Scanning electron microscopy revealed degradation of the F. solani mycelium. Abnormal hyphal swelling and retreating were caused by the lysing agents from P. stutzeri YPL-1, and a penetration hole was formed on the hyphae in the region of interaction with the bacterium; the walls of this region were rapidly lysed, causing leakage of protoplasm. Genetically bred P. stutzeri YPL-l was obtained by transformation of the bacterium with a broad-host-range vector, pKT230. Also, the best conditions for the transformation were investigated.

No abstract

We study the conditions for two-photon classical interference with coherent pulses. We find that the temporal overlap between optical pulses is not required for interference However, coherence within the same inputs is found to be essential for the interference.Comment: 5 pages, 4 figure

No abstract

In recent decades, a conducting polymer film: poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) has been employed as an essential component of flexible electronics used in practical products, owing to obvious advantages of its electrical and mechanical properties. Generally, the PEDOT:PSS shows an high electrical conductivity (>1000 S cm −1), deep work function (>5.0 eV), and good compatibility with other materials such as organic dopants, carbon nanomaterials, and inorganic nanowires, which has opened limitless possibilities for electronic application such as electrodes, charge transport layers, and thermoelectric active materials. [1-8] Some organic dopants include polar solvent additives such as dimethylsulfoxide (DMSO) and glycerol that contribute to a decrease in the Coulomb interactions between PEDOT and PSS chains and changed molecular arrangement of the PEDOT and PSS chains. [9] In addition, some non-ionic polymer surfactants have also been utilized to increase electrical conductivity of the PEDOT:PSS films by forming interconnected PEDOT networks in the PEDOT:PSS films. [10] Despite excellent electrical and mechanical properties, practical application of poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) face the challenge of ensuring air stability in electronic industry. Here, degradation mechanism of PEDOT:PSS-based films in air is clearly demonstrated through X-ray/ultraviolet photoelectron spectroscopy (XPS/ UPS) and its depth-profiling technique. As the duration of air-exposure increases, the PEDOT:PSS-based films alter molecular structures with the formation of SO x bond in PEDOT and CN x bond growth, changing ratios of insulating part (PSS − , PSSH, oxidized PEDOT) to conducting part and deteriorating their electrical conductivities. These transition behaviors are similar in all PEDOT:PSS-based films regardless of additives such as dopant or multi-walled carbon nanotube. Additionally, methanol treatment to various PEDOT:PSS-based films for inducing conformational change between PEDOT and PSS molecules, partly restore the electrical properties of the denatured PEDOT:PSS films. Finally, thermoelectric properties of the PEDOT:PSS-based films are characterized by investigating the effects of air-aging and methanol treatment on electrical conductivities, Seebeck coefficients, and power factors. To sum up, this study provides a useful guideline for establishing a strategy to ensure air stability of PEDOT:PSS-based films by clarifying the degradation mechanism and property recovery methods.

We demonstrate low-noise and efficient frequency conversion by sum-frequency mixing in a periodically poled LiNbO(3) (PPLN) waveguide. Using a 1556 nm pump, 1302 nm photons are efficiently converted to 709 nm photons. We obtain 70% conversion efficiency in the PPLN waveguide and >50% external conversion efficiency with 600 noise counts per second at peak conversion with continuous-wave pumping. We simultaneously achieve low noise and high conversion efficiency by careful spectral filtering. We discuss the impact of low-noise frequency translation on single-photon upconversion detection and quantum information applications.