Switches for Photonic Quantum Information

Routing quantum information encoded in photonic qubits requires active switches that preserve the quantum state. Fast, low-loss implementations of such switches enable multiplexing protocols for efficient single-photon generation and long-distance entanglement swapping. Switches are also key components in time-bin encoding and facilitate exotic state creation for quantum metrology. Here, we present two implementations. The first is a bulk, electro-optic switch that demonstrates polarization-independent switching at ~ hundreds kHz rates. This method is low-loss, but requires high-voltage (~ kilovolt) operation if traditional bulk Pockels cells are used. Faster, low-voltage implementations rely on integrated optics that suffer from high insertion loss. Instead, we can employ mesoscopic devices, large enough to limit optical clipping (thus retaining high transmission), but small enough to have relatively low switching voltages. The second is an ultrafast (~ GHz - THz), all-optical switch that utilizes cross-phase modulation (XPM) of a quantum signal by an intense, co-propagating pump pulse in an optical fiber. This method is vulnerable to wavelength-dependent polarization-mode dispersion, which can be mitigated by utilizing polarization-maintaining fiber.