Quantum Control of Photons, Atoms and Spins

The emerging area of quantum information science is based on exploiting quantum-mechanical effects for faster computing, secure communications, metrology, and simulations. Though several algorithms have been theoretically proposed to carry out these tasks, physical 
realizations are still at a rudimentary state of development. Of crucial importance is the ability to control objects like photons, atoms, electrons, spins etc. at the single-quantum level. Examples of such control include (i) the ability to prepare quantum systems in well-defined initial states, (ii) the ability to coherently manipulate these states, and (iii) the ability to protect these states from loss of coherence caused due to interactions with the environment. My talks will focus on experimental demonstrations of such quantum control

In this first talk I will give a brief overview of the field and then set the stage for tomorrow’s discussion. I will describe a scheme to generate time-frequency entangled pairs of photons in laser-cooled atomic ensembles using electromagnetically-induced transparency and slow light. These photons have linewidths that are much narrower than the widths of atomic transition lines and consequently, coherence lengths that can be as long as 1000 feet. Making a segue from the world of real atoms to that of “artificial” atoms, I will next give a brief introduction to Nitrogen-Vacancy (NV) colour centers. These are point defects in diamond that have attracted wide interest in recent years for their use as qubits for information processing and for ultra-sensitive and high-resolution metrology. I will discuss the 
physics of NV centers and highlight some recently demonstrated applications.