Attosecond ionization time delays (Prof. U. Keller)

The general issue is that time is not an operator in quantum mechanics, and therefore not a direct observable. Following the peak of a wavepacket, for example, can be tricky and often misleading. In contrast to a light pulse, an electron wavepacket disperses even in vacuum. Since the propagation of the peak of the wavepacket is defined by the group delay, almost any group delay can be measured during propagation in combination with an appropriate energy-dependent transmission filter.In principle, time dependent-processes in quantum mechanics are described by the time-dependent Schrödinger Equation (TDSE). The challenge is that the TDSE in most cases cannot be solved without approximations. Semi-classical models, on the other hand, seem to explain – suprisingly well - many current attosecond measurements.  However, there is a strong debate regarding how far such semi-classical models are justified and are not in contradiction with fundamental principles of quantum mechanics. At the same time, attosecond measurements have advanced rapidly with reproducable and high-quality data, allowing for very fundamental tests for our current understanding and models in time-dependent quantum mechanics. This talk will review the recent attosecond ionization dynamics ranging from single-photon [2] to multi-photon emission in the tunneling regime [3, 4]. 

References:
[1]    S. R. Leone, C. W. McCurdy, J. Burgdörfer, L. S. Cederbaum, Z. Chang, N. Dudovich, J. Feist, C. H. Greene, M. Ivanov, R. Kienberger, U. Keller, M. F. Kling, Z. H. Loh, T. Pfeifer, A. N. Pfeiffer, R. Santra, K. Schafer, A. Stolow, U. Thumm, M. J. J. Vrakking, “Attosecond science – What will it take to observe processes “in real time”?”, Nature Photonics, vol. 8, No 3, pp. 162-166, 2014
[2]    M. Sabbar, S. Heuser, R. Boge, M. Lucchini, T. Carette, E. Lindroth, L. Gallmann, C. Cirelli, U. Keller          “Resonance effects in photoemission time delays in argon and neon”, Phys. Rev. Lett., submitted 13. Feb. 2015
[3]    A. S. Landsman, U. Keller, “Attosecond science and the tunneling time problem”, Physics Reports, vol. 547, pp.      1-24, 2015
[4]    A. S. Landsman, M. Weger, J. Maurer, R. Boge, A. Ludwig, S. Heuser, C. Cirelli, L. Gallmann, U. Keller          “Ultrafast resolution of tunneling delay time”, Optica, vol. 1, No. 5, pp. 343-349, 2014