Propagation of Quantum Signal in Plasmonic Waveguides

Quantum photonic integrated circuit (QPIC) based on dielectric waveguides has been widely used in linear optical quantum computation. Recently, surface plasmon was introduced to this area since it can confine and manipulate light beyond the diffraction limit. Here, on-chip quantum interference of two single surface plasmons is realized with dielectric loaded surface plasmon polariton waveguides. The high visibility larger than 90% not only proves the Bosonic nature of single plasmons, but also is feasible for realizing basic quantum logic gates in linear optical quantum computation. The effect of intrinsic losses in plasmonic waveguides on quantum information processing is also discussed. Even though the influence is negligible in this experiment, our studies reveal that loss can reduce the quantum interference visibility dramatically in some cases, which means quantum coherence must be carefully considered when designing QPIC devices.

We also demonstrate for the first time the maintaining of quantum polarization entanglement in a nanoscale hybrid plasmonic waveguide composed of a fiber taper and a silver nanowire. The transmitted state throughout the waveguide has a fidelity of 0.932 with the maximally polarization entangled state Φ+. Furthermore, the Clauser, Horne, Shimony, and Holt (CHSH) inequality test performed, resulting in value of 2.495±0.147 > 2, demonstrates the violation of the hidden variable model. Since the plasmonic waveguide confines the effective mode area to subwavelength scale, it may be used as near-field quantum probe in a quantum near-field micro/nano-scope, which can realize high spatial resolution, ultra-sensitive, fiber-integrated, and plasmon-enhanced detection, as well as bridge nanophotonics and quantum optics.

renxf@ustc.edu.cn