Two-dimensional Fourier transform spectroscopy paper in PRL

Two-dimensional Fourier transform spectroscopy (2dFTS) reveals information about the quantum pathways via which energy is carried through a molecule, or through a complex ensemble of interacting components. 2dFTS can chart the routes taken by quanta of solar energy through complex biological molecules, or reveal the transition of quanta through quantum information architectures. It can reveal the characteristic quantum phase information which is the basis of technological proposals for the development of quantum computing devices, or the dynamical information which could be used to devise biomimetic energy sources.

In this paper we demonstrate a technique to obtain the complete time-dependent polarizability from intensity measurements alone using a phase retrieval technique. The effect is to simplify the experimental setup for 2dFTS and thereby make it more generally applicable. For example, this will allow a complete picture to be obtained from experiments with multi-colour excitation, which otherwise would not be possible.

The details of this technique can be found in Phys. Rev. Lett. 100, 227401 (2008).

The figure shows (a) the 2D correlation spectrum from simulations of a 3-level system, and (b) the equivalent spectrum obtained from the spectrally resolved intensity data alone, using our phase retrieval technique. The agreement between the two is good, but not ideal, and work is progressing well to improve the phase retrieval algorithm and the reconstructed data.