A Large Bandwidth Room Temperature Single Photon Source

• Applicant: Dr. Robert Löw
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428456730

This project is dedicated to the realization of a single photon source based on strong interactions between Rydberg atoms in a thermal vapour. The possibility to produce anti-bunched photons in a gas of Rubidium atoms has been shown very recently in a proof of principle experiment by the applicants. In this experiment we have shown that, in a micron sized excitation volume, the blockade effect is sufficient to allow for only one Rydberg excitation, which can then be transferred to a light mode in a four-wave mixing scheme. This conversion has to happen within the lifetime of the strongly correlated many body state. In our excitation scheme the coherence time is limited by the motion of the atoms to roughly one nano-second. This means that sufficient strong laser pulses are required to achieve GHz Rabi-frequencies. One of the bottlenecks in our experiment is the small repetition rate (50Hz) of our laser-system. In this proposal we want to realize a second generation of the vapour based single photon source, which will be much closer to real applications. First of all, we will switch to a different four-wave mixing scheme, where we can operate the lasers at rates well above 100kHz giving much better photon statistics. Also parts of the optics will be integrated in the vapour cells as solid immersion lenses. To improve the atom-light coupling, we will also add optical coatings to produce low to medium finesse cavities. This coatings will also include protective coatings to a void chemical reactions. On the material side we will investigate how different Rydberg atoms interact with the close by walls made of Quartz, Sapphire, etc. With the new laser system we will also obtain control over the actual pulse shapes down to the 50ps scale, which will require extended numerical simulations to obtain an optimal sequence. Finally we want to prove the scalability of our approach by realizing two single photon sources in one cell and characterize the indistinguishability of the emitted photons in a Hong-Ou-Mandel interferometer.A notable part of this project will be the cooperation with Dr. Ofer Firstenberg (Weizmann Institute of Science, Israel). His group has broad expertise on Rydberg atoms as well as on the spectroscopy on thermal vapours. As both groups have a strong need for vapour cells featuring optical coatings we will develop together the fabrication of such cells.All these measures will increase the photon rate as well the fidelity of our source. One application would be a purely vapour based quantum repeater scheme, where the wavelength and the bandwidth of the single photon source and of the storage is naturally matched. Another application lies in linear quantum computation or in the creation of more complex photon states (higher Fock states, noon-states,...).

• DFG Programme: Priority Programmes
• Subproject of: SPP 1929: Giant Interactions in Rydberg Systems (GiRyd)
• International Connection: Israel
• Co-Investigator: Professorin Dr. Hadiseh Alaeian
• Cooperation Partner: Dr. Ofer Firstenberg