Abstract

The localization of an electron in a symmetric double quantum well by an intense laser pulse has been studied extensively in recent years.^1,3 In the presence of a strong driving field, an electron initially localized in one well will tunnel back and forth between the wells at a frequency equal to the transition frequency between the Floquet states of the system. For certain values of frequency and intensity of the driving field for which the Floquet states become degenerate, the tunneling process is suppressed and the initial localization is maintained. If, in addition to frequency and intensity, the rise time of a smoothly rising pulse action on the system is chosen appropriately, it is possible not only to maintain initial localization but also to localize an electron initially in a delocalized state.^2,3 We show that even-harmonic generation occurs for arbitrary initial conditions, and conclude that initial localization and pulse shaping are not required for symmetry breaking, although they can greatly enhance it in the extremely-strong-field regime.

© 1994 Optical Society of America