Room-temperature rack-mounted quantum buffer for high-rate time-bin qubits

For quantum networks to extend beyond the physical distances defined by the real-world limitations of signal loss, a sophisticated multi-modular network of quantum devices to allow for “repeating” quantum information, without measuring or damaging it, are required. Quantum repeaters create entanglement between remote photons by swapping the entanglement between multiple entanglement sources in a highly synchronized manner. To make these modules work efficiently within the existing telecom fiber infrastructure, it is necessary to be able to coherently buffer and synchronize single photon qubits using quantum buffer. Although significant process has been made towards developing commercial quantum buffers for polarization states, to date there is no available option for buffering time-bin qubits. Time-bin qubits and entangled pairs are resilient to the polarization fluctuations of a optical fibers, turning them into a prime candidate for quantum data transportation. The proposed quantum buffer for time-bin qubits by Qunnect can significantly push forward the development of these networks. Here, we propose a first of its kind, portable room temperature quantum buffer, capable of storing time-bin qubits with high efficiency and long coherence time. The proposed device leverages the atomic transitions of a well-characterized atomic vapor, Rubidium (Rb), to temporarily store photons through the process of gradient echo. A Gradient Echo, or GE-based buffer, is a photon echo technique that uses magnetic fields to reverse the time evolution of an atomic ensemble coherence as a mean to retrieve the qubit at any arbitrary time. This technique can be applied to an inhomogenously broadened excitation, allowing for storage of temporally narrow photons (<10ns) with demonstrated efficiencies above 85%. Additionally, GE-based quantum buffers allow for simultaneous multiplexing in temporal and spatial modes, paving the way for high rate entanglement distribution networks. The proposed technology holds the key to building quantum buffer-assisted, all-optical quantum networks. Our approach allows for distribution of time-bin entangled photons which can preserve the quantum fidelity of the network regardless of the fiber optics phase fluctuations. In the near term, this technology can assist many scientists at the DOE and other agencies with their work towards the national quantum internet. In the long term, US-based and global quantum networks can use our devices in every node to distribute entanglement across the networks.