Switchable Quantum Buffer For Transparent Optical Quantum Network

Quantum buffers are necessary components for realizing practical quantum networks. Although extensive developments on quantum buffers have been reported, they all lack practicality, mainly due to their excessive optical loss that has prevented quantum applications because of the single or low-average photon nature of the transmission signals. To date, no buffer has been successfully converted from a laboratory concept to a deliverable device. We propose to realize an all-fiber optical quantum buffer that is capable of precisely delaying quantum signals in transparent optical quantum communication networks. The novel buffer achieves quantum signal storage using a 2x2 cross electro-optic switch to trap entangled photon pairs inside a low loss fiber loop and release by timed switching. This program seeks to achieve unpresented performance in switching speed and low optical loss that are useful for the entire community to advance the field of quantum communications and networking. In Phase I, we have successfully fabricated a fully functioning fiberoptic quantum buffer. The measurements verified desirable low loss ~0.5 dB, polarization independence, fast switching time ~20ns, and a high repeat rate of 1 MHz. The ultra-low optical loss of less than 0.5 dB sets a world record for fiber- coupled electro-optical switches. We have also successfully demonstrated the storage of an optical pulse for 250 ns via optical pulse buffering and trapping. This Phase I provided us an opportunity to achieve an in-depth understanding of the high-speed electro-optic physics and identified practical ways to improve the buffer performance further to reach lower loss and faster switching in Phase II, including ultra-low optical insertion loss below 0.4 dB; fast rise/fall time below 1 ns; and fast repetition rate over 10 MHz. These performance attributes have not been obtained before. Quantum communications is a revolutionary technology that could open up a universe of applications that are not possible with classical communications, including secure communications, teleportation for quantum communications when only a classical channel is available, and connecting quantum computers together. Quantum communications will alter how we do business in the future. It will fundamentally change how we secure data and security in our technology-driven world. Some see it as one day displacing the Internet in its current form. This game-changing technology is not only critical to our nation's security but also to its future economy.