Time-bin entangled states are a promising paradigm for quantum communication between nodes of a quantum network. In addition, high-dimensional time-bin states are easy to generate and could offer significantly improved transmission fidelity compared to standard qubits. However, the overall rate of these transmissions is necessarily diminished because successive higher-dimensional time-bin states must be delayed such that they do not overlap in time. We propose to alleviate this concern by introducing an optical frequency shift on each time bin, taking advantage of quantum wavelength division multiplexing to greatly increase the rate of communication possible within a quantum channel. Here we report frequency shifts over a range of ∼ 2 nm (∼ 240 GHz) of telecom pulses in two time-bins separated by ∼ 250 ps, consistent with the requirements for multiplexing.
Frequency-encoded quantum information offers intriguing opportunities for quantum communications networks, with the quantum frequency processor (QFP) paradigm promising scalable construction of quantum gates. Yet all experimental demonstrations to date have relied on discrete fiber-optic components that occupy significant physical space and impart appreciable loss. We introduce a model for designing QFPs comprising microring resonator-based pulse shapers and integrated phase modulators. We estimate the performance of frequency-bin Hadamard gates, finding high fidelity values sustained for relatively wide-bandwidth frequency bins. Our simple model and can be extended to other material platforms, providing a design tool for future frequency processors in integrated photonics.
Two main challenges for quantum networks are state preservation and scaling current infrastructure. Photonic polarization qubits are susceptible to effective decoherence via polarization mode dispersion in optical fibers. This can be circumvented by encoding qubits in the photon’s arrival time, i.e., time-bin encoding. Here, we present measurements on a thin-film lithium niobate integrated-optic device, designed to analyze telecom-wavelength photonic time-bin qubits. By thermo-optically tuning the phase and amplitudes of interfering processes traversing the photonic circuit on the device, we are able to obtain ∼ 83% interference visibility, marking significant progress towards efficient time-bin encoding and analysis with integrated photonics.
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