Quantum Network Node

Neutral atoms interacting with single photons are a fascinating experimental platform that has been explored in the last decades for a series of applications in quantum science. A highlight in the history of this research was the awarding of the Nobel Prize to Serge Haroche in 2012. Over the last years, it turned out that neutral atoms trapped at the center of an optical cavity are a promising platform for the implementation of a novel kind of communication network that is based on the laws of quantum mechanics. The practical implementation of this quantum internet is an open challenge tackled by many research groups worldwide. The general idea is to employ the strong atom-light interaction provided by the cavity to implement an efficient interface between atoms and photons. This allows processing of quantum information within the network nodes. Additionally, the photons may also propagate to other nodes in the network and can therefore be employed as flying carriers of quantum information. Landmark experiments have been performed with this experimental platform, but the performance of state-of-the-art setups was limited because - due to a stochastic atom-loading procedure - it was practically not possible to work with more than two individually controlled neutral atoms trapped in each of the network nodes. 

Fortunately, there is a solution to this challenge provided by optical tweezers which were pioneered by Nobel laureate Arthur Ashkin. Optical tweezers are tightly focused laser beams in which single atoms can be trapped and positioned with high precision. Injecting many tweezers into a reservoir of cold atoms from a magneto-optical trap allows for stochastic loading of a tweezer array with a success probability of about 50% per tweezer trap. Taking a picture of the array then allows identifying the empty tweezer traps. The occupied traps are rearranged to an ordered array which is continuously refilled from a spatially separated reservoir. Combining the optical tweezer platform with an optical cavity will combine the advantages of both experimental platforms and enable working with N>2 individually controlled atoms in the cavity mode. This is the mission of the Quantum Network Node group. The envisioned system is shown in Fig. 1 and comprises a set of atoms coupled to the cavity mode. Outside of the cavity mode resides the reservoir which allows replacing intracavity atoms in case one of them is lost from its respective tweezer trap.