Wave packet (WP) interferometry is a clear manifestation of wave nature of matter, and is a basic scheme of controlling a variety of quantum systems from simple atoms to nano structures with possible applications to novel quantum technologies such as bond-selective chemistry and quantum computation. The key technique in the WP interferometry is fine tuning of the delay between two light pulses that produce a pair of WP's with a precision far better than the quantum oscillation cycle of the WP's, say few femtoseconds (fs) to attoseconds (as). The WP's are then phase-locked and produce stable interference. Kenji Ohmori of IMS in Japan and his colleagues (Y. Sato, E. E. Nikitin, S. A. Rice) have constructed an “attosecond phase modulator (APM)”: a device for tuning the delay between two UV fs pulses with sub-10 as precision. They have utilized this APM to create an unprecedented high-precision WP interferometer with a dilute ensemble of the HgAr van der Waals complex; their interferometer displayed almost 100% fringe contrast as a function of the delayτ between two UV fs pulses around 250 nm. Moreover they have demonstrated the dephasing and rephasing of the interferograms of consecutive vibrational eigenstates within WP's, which arise from a subtle difference in the quantum oscillation cycles of each eigenstates, different from the well-known collapse and revival of the electron WP's in atoms (see Yeazell et al., Physical Review Letters 23 April, 1990). Their high precision interferometer makes it possible to create virtually arbitrary relative superpositions of the three vibrational eigenstates within a WP only by tuning a single parameterτ. It is pointed out that the interference structure can be retrieved from the population information stored in the thermal ensemble of molecules even after the coherence is wiped out. All these features are quite general in WP interference and therefore provide basis for opening new perspective of coherent control in a wide variety of quantum systems. (Ohmori et al., Physical Review Letters 91, 243003 (2003); contact Kenji Ohmori, ohmori_at_ims.ac.jp, 81-564-55-7361)
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Fig. 1. An example of the quantum interferograms of two molecular wave packets moving on the A(30+)-state potential curve of the Hg-Ar vdW complex. The quantity τ0 denotes the value for the inter-pulse delay τ at the left edge of the graph. The interferogram displays almost 100% fringe contrast as a function of τ tuned with sub-10 attoseconds precision. Its top and bottom represent amplification and annihilation of the wave packet, which are also shown in the theoretical simulations.
Professor Kenji Ohmori
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