Deterministic Photon-Photon interactions
In my PhD thesis, I work with single atoms trapped at the center of a high-finesse optical cavity. The atoms interact strongly with single photons reflected from the cavity. As was shown in previous experiments in the group of Prof. Rempe, a quantum gate between a single atom and a single photon can be implemented employing this experimental platform .
Artist´s view of the photon reflection process in the implementation of the photon-photon gate. The cavity contains a single atom (red sphere with yellow electron orbitals). Two photons are successively reflected from the cavity.
Based on this result, the implementation of a quantum gate between two photons mediated by
an atom was realized experimentally during my PhD thesis . This result was a long
standing goal in optical quantum information processing since it paves the way towards scalable optical quantum computing due to its deterministic nature. The implementation of such a gate is achieved by reflecting two photons (control and target) from the atom-cavity system successively. The gate requires a deterministic interaction of an atom and a photon which is so strong that a single control photon can influence a target photon by changing the state of the atom as an intermediate step. Afterwards, the target photon interacts with the atom and is influenced by its state. The nonlinear atom-cavity system provides the necessary platform to achieve this strong interaction.
 A. Reiserer, N. Kalb, G. Rempe, & S. Ritter “A quantum gate between a flying optical photon and a single trapped atom”, Nature, 508 237-240 (2014)
 B. Hacker, S. Welte, G. Rempe, S. Ritter, “A photon-photon quantum gate based on a single atom in an optical resonator”, Nature 536, 193-196 (2016)
 F. Meinert, C. Basler, A. Lambrecht, S. Welte, and H. Helm, “Quantitative analysis of the transient response of the refractive index to conditions of electromagnetically induced transparency”, Phys. Rev. A85, 013820 (2012)
 S. Welte, C. Basler, and H. Helm, “Studies of Berry’s phase and its sign in quantum superposition states of thermal 87Rb atoms”, Phys. Rev. A89, 023412 (2014)
2014: NIM workshop at Glocknerhaus (Austria), “Nondestructive detection of an optical photon” (talk)
2015: ExQM seminar (Munich), “Nondestructive detection of an optical photon” (talk)
2015: Young Atom Opticians conference (Zurich), “Optimisation of an atom-photon quantum gate” (poster)
2015: Resonator QED conference (Munich), “Optimisation of an atom-photon quantum gate” (poster)
2016: DPG spring meeting (Hannover), “A cavity-mediated photon-photon gate” (poster)
2016: ExQM seminar (Munich), “A photon-photon quantum gate” (talk)
2016: Gordon Conference on Quantum science (Stonehill College, USA), “A cavity-mediated photon-photon gate” (poster)
Short CV and project description
Max-Planck-Institute of Quantum Optics
85748 Garching bei München
phone: +49 89 3 29 05 – 398 // -371