Optical Quantum Network Time-Frequency Multiplexer (5c)

As progress in quantum information and computation leads to ground-breaking advances, there is a critical need to realize quantum networks. Of the different encoding methods, time-bin encoding is both common and advantageous for quantum networks, however, scaling time-bin-based quantum networks poses two key challenges. First, these networks require identical phase-locked delay lines within each networking node to handle the time- encoded quantum information. Increasing time-bin count requires more delays that must also be phase locked throughout the network, increasing complexity. Second, combating low rates arising from fiber losses—even with quantum repeaters—requires higher bandwidths. As laying additional fibers to increase bandwidth is cost prohibitive, multiplexing becomes necessary, particularly, spectral multiplexing to utilize the full capacity of fiber. An ideal scalable quantum network should avoid the complexities of delay-line phase locking and exploit multiplexing to increase optical bandwidth. To solve this challenge, this program will develop photonic chip-based time-to-frequency multiplexers to convert time-bin quantum information to frequency-division multiplexed signals within a single time-bin— effectively ‘stacking’ multiple time bins—that will be transmitted efficiently through fiber and demultiplexed using a complimentary chip. To achieve time-to-frequency multiplexing, our chip contains three stages. First, a time-bin combiner uses 1×2 switches and delays to separate and retime the quantum information pulses into one time slot on different physical channels. Next, RF-driven resonators shift the frequency of each channel. Lastly, a series of add/drop filters spectrally combine the channels onto a common bus finishing the time-to-frequency multiplexing. This frequency-stacked quantum information could be further multiplexed using time-division multiplexing on the same chip. In Phase I, we will leverage our ongoing chip-based time-bin entanglement work as well as telecommunications-wavelength frequency shifters to create time-to-frequency multiplexing chips. We will design, fabricate, and evaluate prototype devices to demonstrate this capability, showing both multiplexing and demultiplexing at classical and quantum light. Phase I will target a pair of frequency bins offset by 5 GHz to pave the way for a Phase II effort that will target 8 or more time bins. Our time-to-frequency multiplexing technology will enable multiplexing of quantum-entanglement data over current fiber-based networks, greatly increasing the capacity of near-term quantum networks without the burden of laying additional dedicated fiber. This approach will reduce initial quantum-network infrastructure to expedite some of the first quantum networks. These devices will become a key component for every node within a quantum network, which will enable advanced quantum computing, secure communication, and quantum sensing.