Picosecond Timing Resolution Detection of Gamma Photons Utilizing   Microchannel-plate Detectors: Experimental Tests of Quantum Nonlocality and   Photon Localization
  The concept and subsequent experimental verification of the proportionality between pulse amplitude and detector transit time for microchannel plate detectors is presented. This discovery has led to considerable improvement in the overall timing resolution for detection of high energy gamma photons. Utilizing a 22Na positron source, a full width half maximum (FWHM) timing resolution of 138 ps has been achieved. This FWHM includes detector transit-time spread for both chevron-stack type detectors, timing spread due to uncertainties in annihilation location, all electronic uncertainty, and any remaining quantum mechanical uncertainty. The first measurement of the minimum quantum uncertainty in the time interval between detection of the two annihilation photons is reported. The experimental results give strong evidence against instantaneous spatial-localization of gamma photons due to measurement-induced nonlocal quantum wave-function collapse. The experimental results are also the first that imply momentum is conserved only after the quantum uncertainty in time has elapsed [H. Yukawa, Proc. Phys. -Math. Soc. Japan, 17, 48 (1935)]. 
Victor D. Irby