Phase-preserving amplification near the quantum limit with a Josephson ring modulator. - Bergeal, N.; Schackert, F.; Metcalfe, M.; Vijay, R.; Manucharyan, V. E.; Frunzio, L.; Prober, D. E.; Schoelkopf, R. J.; Girvin, S. M.; Devoret, M. H. (Nature, 2010)