Optically Engineered Quantum States in Ultrafast and Ultracold Systems

Sylvain de Léséleuc, Yuki Torii Chew, Takafumi Tomita +3 more

By combining techniques from the ultracold atom and ultrafast laser communities, we explore the interaction between Rydberg atoms in tweezers on the nanosecond timescale and open the path towards ultrafast quantum engineering with Rydberg atoms.

Ivan Deutsch

Hugo E. L. Martay, David J. McCabe, Duncan G. England +3 more

Calculations relating to two experiments that demonstrate coherent control of preformed rubidium-85 molecules in a magneto-optical trap using ultrafast laser pulses are presented. The two experiments are a step toward the stabilization of ultracold rubidium dimers using ultrafast lasers. In the first experiment, it is shown that preassociated molecules in an incoherent mixture of states can be made to oscillate coherently using a single ultrafast pulse. A mechanism that can transfer molecular population to more deeply bound vibrational levels is used in the second. Optimal parameters of the control pulse are presented for the application of the mechanism to molecules in a magneto-optical trap. The calculations make use of an experimental determination of the initial state of molecules photoassociated by the trapping lasers in the magneto-optical trap and use shaped pulses consistent with a standard ultrafast laser system. The experiment's purpose is to demonstrate and evaluate the use of ultrafast shaped pulses to manipulate ultracold rubidium dimers with a view to the eventual stabilization of the molecules.

Kang-Kuen Ni

Duncan G. England

In the ultracold regime, where the interactions between atoms become quantum mechanical in nature, we can investigate the fundamental properties of matter. A natural progression from the catalogue of pioneering experiments using ultracold atoms is to extend the size of our quantum system by producing ultracold molecules in prescribed low-energy internal states. Techniques for cold molecule production are split into two methods: direct and indirect cooling. While direct cooling methods have yet to realize ultracold temperatures, collisional relaxation in the molecules leads to low internal energy states. By contrast, indirect cooling — the association of molecules from pre-cooled atoms—has produced a range of molecules at ultracold temperatures; the challenge with this technique is to control the internal state.This thesis concentrates on a technique that is complementary to those already in existence: ultrafast photoassociation. Key to this technique is the formation of time non-stationary wavepackets in the excited-state in order to improve FranckCondon overlap of the excited state with deeply bound ground-state vibrational levels. A pump-probe experiment was designed and built to demonstrate the formation of bound excited-state dimers. In this work we show that the initial state from which the wavepacket originates is of critical importance to the evolution of excited-state population. We find that the internuclear separation of the wavepacket produced in a rubidium magneto-optical trap is too large to observe coherent oscillations in the excited state. The implications of this are discussed along with recommendations for future ultrafast photoassociation experiments. Consequently, a new ultracold atom apparatus was built utilizing magnetic and dipole-force trapping to increase the density of the atomic sample; this apparatus will enable future experiments combining the exciting fields of ultracold matter and ultrafast light.

Gyu-Boong Jo