Noise Auto-correlation Spectroscopy

Traditional methods of nonlinear laser spectroscopy rely on the coherence of laser pulses as it determines the resolution of a spectroscopic measurement. We have developed a new spectroscopic method in which noise and decoherence are introduced deliberately to increase spectral resolution, robustness and efficiency of CARS. Our approach combines the efficiency and resolution of a coherent process with the robustness of incoherent light, and can be implemented in a simple optical setup because it relies on random noise rather than on an accurate spectral or temporal pulse shaping.

Nature Physics 4, 125-129 (2008), arxiv.org:0710.3173

Narrowband Spectroscopy by Correlation of Broadband Pulses

High peak power ultrafast lasers are widely used in nonlinear spectroscopy but often limit its spectral resolution because of the broad frequency bandwidth of ultrashort laser pulses. Improving the resolution by achieving spectrally narrow excitation of, or emission from, the resonant medium by means of multi-photon interferences has been the focus of many recent developments in ultrafast spectroscopy. We have introduced an alternative approach, in which high resolution is exercised by all-optical detection of narrow spectral correlations between broadband excitation and emission optical fields.

Phys. Rev. A (Rap Comm) 79, 031801R (2009).arxiv.org:0808.1924

Piecewise Adiabatic Passage: Theory

We have developed a new method of executing complete population transfers between quantum states using a series of femtosecond laser pulses. The method can be applied to a large class of problems as it benefits from the high peak powers and large spectral bandwidths afforded by femtosecond pulses. The degree of population transfer is robust to a wide variation in the absolute and relative intensities, durations, and time ordering of the pulses.

Phys. Rev. Lett. Phys. 99, 033002 (2007)

In collaboration with the group of Moshe Shapiro

Piecewise Adiabatic Passage: Experiment

We have demonstrated a new technique of adaiabatic population transfer between two quantum states by piecewise chirping of ultrashort laser pulses. Coherent excitation of a two-level system with a train of laser pulses is shown to reproduce the effect of an adiabatic passage, conventionally achieved with a single frequency-chirped pulse. By properly adjusting the amplitudes and phases of the pulses in the excitation pulse train, we achieve complete and robust population transfer to the target state. We show that similarly to the conventional adiabatic passage, the piecewise process is insensitive to the total excitation energy as long as the adiabaticity conditions are satisfied. The piecewise nature of the process suggests that robust and selective population transfer could be implemented in a variety of complex quantum systems beyond the two-level approximation.

Phys. Rev. Lett. 100, 103004 (2008), arxiv.org:0710.3145

Adiabatic Passage into Shaped Wavepackets

The method of piecewise adiabatic passage allows us to match the temporal profile of the excitation field to the internal molecular dynamics, and as a result, to populate efficiently complex wavepackets instead of a single quantum state. The complexity of the excited wavepackets, e.g. the relative amplitudes and phases of the participating eigenstates, can be further controlled by the spectral shaping of the excitation pulses, thus enabling state-selective chemistry. Efficient population transfer into a particular set of states among many available molecular levels is also important for many applications of coherent control in cold molecules and the realization of quantum computing operations.

Phys. Rev. A. 79, 023422 (2009). In collaboration with the group of Moshe Shapiro

Dynamics of photon localization in random media

We are studying the propagation of ultrashort laser pulses in one-dimensional random media. Light becomes "trapped", or localized, in such layered structures due to the constructive interference of waves following time reversed paths. Though it is well known that localization can always be achieved in sufficiently large low-dimensional samples, the dynamics of this process is not well understood. "How localization happens in time?" is the central question of this project.

In collaboration with the group of Azriel Genack