SEMINAR: Physics Seminar

Single photons and single atoms are important carriers of quantum information. Using a network of atoms that are coupled to one another by single photons [1], it is possible to generate a cluster state: a highly entangled state that can be used as a resource for quantum computation.

We have developed a deterministic source of single photons based on a single atom strongly coupled to an optical cavity [2]. The atom is driven to emit single photons in to the cavity mode using the coherent process of vacuum-STIRAP. Furthermore, by changing the driving laser pulse, we can precisely control the amplitude and phase of the photon wavepacket. We observe the effect of changing the phase of the photon on the Hong-Ou-Mandel interference between two successive photons. Using the reverse process, we aim to reabsorb these single photons with a second atom-cavity system, thus generating an entangled state between two distant atoms.

In addition, we are working on a method to trap and control single atoms with optical tweezers [3]. The tweezers are based on a highly focussed red-detuned dipole trapping laser. The shape of the trapping beam is controlled using a spatial light modulator (SLM) in order to produce arbitrarily-shaped trapping potentials. We demonstrate the ability of this setup to trap and dynamically transport small clouds of atoms, and show how this can be integrated with a network of fibre-tip optical cavities

[1] A. Kuhn and D. Ljunggren, Cavity-based single-photon sources, Contemporary Physics 51, 289 (2010)

[2] Peter B R Nisbet-Jones et al, Highly efficient source for indistinguishable single photons of controlled shape, New J. Phys. 13 103036 (2011)

[3] Cecilia Muldoon et al, Control and Manipulation of Cold Atoms in Optical Tweezers, arXiv:1109.0657 (2011)