Optical Quantum Network Time-Frequency Multiplexer

C53-05c-271150As 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, spectral multiplexing becomes necessary. This program is developing photonic chip-based time-to-frequency multiplexers to convert time-bin quantum information to frequency-division multiplexed signals within a single time-bin that will be transmitted efficiently through fiber and demultiplexed using a complimentary chip. To achieve time-to- frequency multiplexing, this program is developing photonic chips containing 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 a successful Phase I, this program as demonstrated time-to-frequency multiplexing using a bulk lithium niobate modulator with two-time bins with a frequency shift of ~60 GHz (0.5 nm). To scale this approach to higher time-bin counts, this program has designed, fabricated, and tested key thin-film lithium niobate subcomponents including low-loss waveguides, edge coupler, and ring-resonator based frequency shifters, showing the viability of this approach. Within Phase II, through iterative design, fabrication, and testing cycles, this program will fully develop packaged integrated time-to-frequency multiplexing units, perform measurements at both classical and single-photon light levels, and observe the effect on the quantum state after passing through a multiplexer and demultiplexer within a time-to-frequency multiplexed link. Lastly, this program will increase the number of frequency channels through an iterative design cycle. This Phase II effort will result in a proof- of-concept time-to-frequency multiplexed link to greatly enhance the bandwidth of quantum networks. 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.