Coherent Control in Atoms, Molecules and Solids

Pötz, Walter, W. Andreas Schroeder

Thomas C. Weinacht

Axel André, David P. DeMille, John M. Doyle +5 more

The challenge of building a scalable quantum processor requires consolidation of the conflicting requirements of achieving coherent control and preservation of quantum coherence in a large scale quantum system. Moreover, the system should be compatible with miniaturization and integration of quantum circuits. Mesoscopic solid state systems such as superconducting islands and quantum dots feature robust control techniques using local electrical signals and self-evident scaling based on advances in fabrication; however, in general the quantum states of solid state devices tend to decohere rapidly. In contrast, quantum optical systems based on trapped ions and neutral atoms exhibit dramatically better coherence properties, while miniaturization of atomic and molecular systems, and their integration with mesoscopic electrical circuits, remains an important challenge. Below we describe methods for the integration of a single particle system -- an isolated polar molecule -- with mesoscopic solid state devices in a way that produces robust, coherent, quantum-level control. The methods described include the trapping, cooling, detection, coherent manipulation and quantum coupling of isolated polar molecules at sub-micron dimensions near cryogenic stripline microwave resonators. We show that electrostatically trapped polar molecules can exhibit strong confinement and fast, purely electrical gate control. Furthermore, the effect of electrical noise sources, a key issue in quantum information processing, can be suppressed to very low levels via appropriate preparation and manipulation of the polar molecules. Our setup provides a scalable cavity QED-type quantum computer architecture, where entanglement of distant qubits stored in long-lived rotational molecular states is achieved via exchange of microwave photons.

Bruce W. Shore

The use of laser pulses to alter the internal quantum structure of individual atoms and molecules has applications in quantum information processing, the coherent control of chemical reactions and in quantum-state engineering. This book presents the underlying theory of such quantum-state manipulation for researchers and graduate students. The book provides the equations, and approaches for their solution, which can be applied to complicated multilevel quantum systems. It also gives the background theory for application to isolated atoms or trapped ions, simple molecules and atoms embedded in solids. Particular attention is given to the ways in which quantum changes can be displayed graphically to help readers understand how quantum changes can be controlled.

Keith Adam Nelson

Hiroyuki Katsuki, Kenji Ohmori

Coherent control is a technique to manipulate the amplitudes and phases of wave functions by exploiting the coherent property of light. It is of great importance for the development of quantum technologies including quantum information processing and chemical reaction control as well as for addressing fundamental problems in quantum mechanics such as the quantum–classical boundary. In this chapter, we describe the development and applications of coherent control based on wave-packet interferometry with attosecond precision, which has been made possible by tuning the delay between two laser pulses on the attosecond time scale. This technique has been applied to several different hierarchies from simple to complex quantum systems: (i) isolated iodine molecules in the gas phase, (ii) molecular crystals of para-hydrogen, and (iii) single crystals of bismuth. In system (i), we have controlled and visualized the interference of vibrational wave packets in the isolated iodine molecules, and that wave-packet interference has been utilized to develop a molecular computer, which executes ultrafast Fourier transform. In system (ii), we have manipulated vibrational wave-functions delocalized in a para-hydrogen crystal. The long coherence lifetime of para-hydrogen crystals is a promising resource to preserve quantum information in bulk solids. In system (iii), we have controlled the excitation ratio of two orthogonal coherent phonon modes, whose coherent superposition has allowed for active control of ultrafast two-dimensional atomic motions in a single crystal of bismuth. Those atomic motions have been visualized by density functional theory calculations. Finally, the coherent control of an ensemble of ultracold Rydberg atoms is briefly discussed as future perspectives for exploring the quantum–classical boundary.