COIN – Coherence Observation by Interference Noise In the traditional wave packet interferometry, a coherent pair of phase-locked laser pulses is applied to a quantum transition in molecules (atoms), and the interference component of the total resulting excitation serves as a signal that reflects the coherent dynamics of the system. Conventional wave packet interferometry requires a good control over the relative phase between pulses, and needs highly stable interferometers. Several years ago we suggested (in collaboration with Y. Prior and his experimental group) the COIN (Coherence Observation by Interference Noise) technique, that concentrates on quantum fluctuations in the population of a quantum system excited by a pair of time-delayed, randomly phased short laser pulses. Although the interference is not present in the mean signal, the effect of quantum interferences can still be felt by measuring the fluctuations of the signal about its mean value. Our first COIN experiments were performed on atomic Potassium vapor. They measured the transverse decay time (T2) of an optical transition in Potassium, and observed oscillation beats in the noise intensity (at 580 fsec), which result from 4S-4P doublet energy splitting in the same atom. The method was shown to be robust, with inherent time resolution of a few optical cycles, despite the use of much longer laser pulses. Several spectroscopic measuring devices based on this principle were proposed and patented in Israel, Europe and the US. Recently, we extended the theoretical basis of the technique to the molecular wave packet interferometry, and showed how it is possible to monitor molecular vibrational dynamics by using COIN. First femtosecond experiments on molecular COIN were performed in the group of H. Kauffmann (University of Vienna, Austria).

• O.Kinrod, I.Sh. Averbukh and Yehiam Prior, "Measuring Coherence While Observing Noise", Phys.Rev.Lett. 75, 3822 - 3825 (1995).
• Y. Prior, O. Kinrod and I.Sh. Averbukh, Israel patent 11331195, European patent 96302444.3-2213,US patent No. 5,805,282.
• C. Leichtle, W.P. Schleich, I.Sh.Averbukh, and M. Shapiro, "Wavepacket interferometry without phase-locking", J.Chem.Phys. 108, 6057 - 6067 (1998).
• Ch. Warmuth, A. Tortschanoff, F. Milota, M. Shapiro, Y. Prior, I.Sh. Averbukh, W. Schleich, W. Jakubetz, and H.F. Kauffmann, "Studying vibrational wavepacket dynamics by measuring fluorescence interference fluctuations", J.Chem.Phys. 112, 5060-5069 (2000).
• Ch. Warmuth, A. Tortschanoff, F. Milota, M. Leibscher, M. Shapiro, Y. Prior, I.Sh. Averbukh, W. Schleich, W. Jakubetz, and H.F. Kauffmann, "Signatures of Molecular Quantum Dynamics in Thermal System: Fractional Wave Packet Revivals Probed by Random-Phase Fluorescence Interferometry", J. Chem. Phys. 114, 9901-9910 (2001).