[1] Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA
[2] Texas A&M Univ, Dept Phys, College Stn, TX 77843 USA
[3] Hamamatsu Photon KK, Cent Res Labs, Hamakita Ku, Hamamatsu, Shizuoka 4348601, Japan
[4] Swiss Fed Inst Technol, Inst Quantum Elect, CH-8093 Zurich, Switzerland