Interaction-based quantum metrology showing scaling beyond the Heisenberg limit

Quantum metrology aims to use entanglement and other quantum resources to improve precision measurement. An interferometer using N independent particles to measure a parameter χ can achieve at best the standard quantum limit of sensitivity, δχ?∝?N(-1/2). However, using N entangled particles and exotic states, such an interferometer can in principle achieve the Heisenberg limit, δχ?∝?N(-1). Recent theoretical work has argued that interactions among particles may be a valuable resource for quantum metrology, allowing scaling beyond the Heisenberg limit. Specifically, a k-particle interaction will produce sensitivity δχ?∝?N(-k) with appropriate entangled states and δχ?∝?N(-(k-1/2)) even without entanglement. Here we demonstrate 'super-Heisenberg' scaling of δχ?∝?N(-3/2) in a nonlinear, non-destructive measurement of the magnetization of an atomic ensemble. We use fast optical nonlinearities to generate a pairwise photon-photon interaction (corresponding to k = 2) while preserving quantum-noise-limited performance. We observe super-Heisenberg scaling over two orders of magnitude in N, limited at large numbers by higher-order nonlinear effects, in good agreement with theory. For a measurement of limited duration, super-Heisenberg scaling allows the nonlinear measurement to overtake in sensitivity a comparable linear measurement with the same number of photons. In other situations, however, higher-order nonlinearities prevent this crossover from occurring, reflecting the subtle relationship between scaling and sensitivity in nonlinear systems. Our work shows that interparticle interactions can improve sensitivity in a quantum-limited measurement, and experimentally demonstrates a new resource for quantum metrology.     

Methylmercury sexual dimorphism in the mouse

Summary 5–8 days after a single nontoxic dose of radioactive methylmercury chloride adult male mouse kidneys contain twice as much radioactive mercury per unit wet wt as do kidneys of similarly dosed adult females.This investigation was supported in part by NSF (RANN) grants (GI-30097 and AEN75-14889), by Program Project grant (ES-01248) and Center grant (ES-01247) from the NIEHS, and in part by the US Department of Energy at the University of Rochester Department of Radiation Biology and Biophysics and has been assigned Report No. UR-3490-1308.     

Histone acetylation in scrapie-affected mouse brain

Zusammenfassung Im Gehirn von Mäusen mit Traberkrankheit (Scrapie) war die Azetylierung von Histonen um 25% erhöht. Diese chemische Änderung erschien weitaus früher als klinische Symptome und histologisch-pathologische Veränderungen. Die Beziehung von Azetyl-Histonen zu Deoxyribonukleinsäuren und ihre Verhältnisse zur Aktivierung von spezifischen Nervenzellen werden kurz besprochen.