Artificial Coherent States of Light by Multiphoton Interference in a Single-Photon Stream.

Coherent optical states consist of a quantum superposition of different photon number (Fock) states, but because they do not form an orthogonal basis, no photon number states can be obtained from it by linear optics. Here we demonstrate the reverse, by manipulating a random continuous single-photon stream using quantum interference in an optical Sagnac loop, we create engineered quantum states of light with tunable photon statistics, including approximate weak coherent states. We demonstrate this experimentally using a true single-photon stream produced by a semiconductor quantum dot in an optical microcavity, and show that we can obtain light with g^{(2)}(0)→1 in agreement with our theory, which can only be explained by quantum interference of at least 3 photons. The produced artificial light states are, however, much more complex than coherent states, containing quantum entanglement of photons, making them a resource for multiphoton entanglement.

Intracellular pH and Survival of Listeria monocytogenes Scott A in Tryptic Soy Broth Containing Acetic, Lactic, Citric, and Hydrochloric Acids.

To study the effect of citric, acetic, lactic, and hydrochloric acids on Listeria monocytogenes Scott A, growth, survival, and intracellular pH (pHin) values were determined during growth in a pH-controlled fermentation vessel. Under the experimental conditions, L. monocytogenes Scott A grown in tryptic soy (plus yeast extract) broth survived even when the pH was reduced to 3.5. For most acids, L. monocytogenes maintained a pH gradient (intracellular pH-external pH) of about 1.0 pH unit and a pHin near 5.0. When the citric and lactic acid-treated cells at pH values 3.5, 4.0, and 4.5 were incubated for a longer time (24 h), both the pH gradient and the pHin values decreased. Although citric and lactic acids were more effective in lowering the pHin, acetic acid had the greatest effect on cell survival. A greater than 4-log reduction in cell number occurred when L. monocytogenes was held in acetic acid-treated broth for 24 h at pH 3.5 even though the pHin was 5.0. The results suggest that inhibition of L. monocytogenes by acids is caused not by a decrease in the intracellular pH, per se, but rather by specific effects of undissociated acid species on metabolic or other physiological activities.