Observation of ground-state quantum beats in atomic spontaneous emission

We report ground-state quantum beats in spontaneous emission from a continuously driven atomic ensemble. Beats are visible only in an intensity autocorrelation and evidence spontaneously generated coherence in radiative decay. Our measurement realizes a quantum eraser where a first photon detection prepares a superposition and a second erases the "which-path" information in the intermediate state.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter

Feedback in a cavity QED system for control of quantum beats

Conditional measurements on the undriven mode of a two-mode cavity QED system prepare a coherent superposition of ground states which generate quantum beats. The continuous system drive induces decoherence through the phase interruptions from Rayleigh scattering, which manifests as a decrease of the beat amplitude and an increase of the frequency of oscillation. We report recent experiments that implement a simple feedback mechanism to protect the quantum beat. We continuously drive the system until a photon is detected, heralding the presence of a coherent superposition. We then turn off the drive and let the superposition evolve in the dark, protecting it against decoherence. At a later time we reinstate the drive to measure the amplitude, phase, and frequency of the beats. The amplitude can increase by more than fifty percent, while the frequency is unchanged by the feedback.Comment: 13 pages, 5 figures, ICAP 2012 23rd International Conference on Atomic Physic

Bacteriocin Producing Lactobacilli Strains as a Biological Strategy to Control Listerial Growthc

Listeria monocytogenes causes listeriosis in humans and animals, and is predominantly transmitted by ingestion of contaminated food. Its severity and high mortality rate make listeriosis a relevant foodborne disease. Currently, biological strategies using probiotic lactobacilli to prevent and control infectious diseases are being globally investigated. The biocontrol exerted by certain Lactobacillus spp. is mainly due to the production of a variety of antimicrobial substances. The aims of this work were (1) to investigate the presence of Listeria spp. in raw cow milk and (2) to determine the inhibitory activity of bacteriocin-like inhibitory substances (BLIS-es) produced by Lactobacillus fermentum L23 and Lactobacillus rhamnosus L60 on L. monocytogenes and other listerial species isolated from food and clinical samples. The presence of Listeria spp. in raw milk was evaluated in 814 samples from 238 cows. The listerial prevalence in cattle was 0.84% and the isolates were identified as L. innocua (LI1) and L. welshimeri (LW1). A total of 29 listerial strains were used as indicator microorganisms to evaluate the antimicrobial activity of BLIS-es L23 and L60. Bioactive metabolites produced by these lactobacilli strains were able to inhibit the listerial growth. This biological activity was mainly attributed to the BLIS-es L23 and L60 which, even at low concentration, were active on 100% of listerial strains. This study reveals a strong potential for the biotechnological use of these bacteriocin producing lactobacilli as a biostrategy against Listeria spp

From quantum feedback to probabilistic error correction: Manipulation of quantum beats in cavity QED

It is shown how to implement quantum feedback and probabilistic error correction in an open quantum system consisting of a single atom, with ground- and excited-state Zeeman structure, in a driven two-mode optical cavity. The ground state superposition is manipulated and controlled through conditional measurements and external fields, which shield the coherence and correct quantum errors. Modeling of an experimentally realistic situation demonstrates the robustness of the proposal for realization in the laboratory

Conditional control of quantum beats in a cavity QED system

We probe a ground-state superposition that produces a quantum beat in the intensity correlation of a two-mode cavity QED system. We mix drive with scattered light from an atomic beam traversing the cavity, and effectively measure the interference between the drive and the light from the atom. When a photon escapes the cavity, and upon detection, it triggers our feedback which modulates the drive at the same beat frequency but opposite phase for a given time window. This results in a partial interruption of the beat oscillation in the correlation function, that then returns to oscillate.Comment: 9 pages, 5 figures, XVII Reuni\'on Iberoamericana de \'Optica, X Encuentro de \'Optica, L\'aseres y Aplicaciones (RIAO-OPTILAS-2010