Efficient plamonics quantum processor
Fabio Antonio Bovino
Quantum Technologies Lab FINMECCANICA-SELEX, via G. Puccini 2, 16154 Genova
Scienze di Base Applicate all’Ingegneria Università La Sapienza, via A. Scarpa 16, 0161, Roma
All-optical quantum computing became feasible when, in 2001, a breakthrough known as the KLM (Knill-Laflamme-Milburn) scheme showed that scalable quantum computing is possible using only single-photon sources and detectors, and linear optical circuits. This scheme relies on quantum interference with auxiliary photons at a beam splitter and single-photon detection to induce not-deterministic interactions. In the past ten years, the KLM scheme has moved from a mathematical proof of concept, towards practical realization, with demonstrations of simple quantum algorithms and theoretical developments that dramatically reduce the resource overhead. Today, efforts are focused on the realization of high efficiency single-photon detectors and sources, devices that would enable a deterministic interaction between photons, and chip-scale waveguide quantum circuits. However, despite integration, the actual physical dimensions are still several centimeters, which render current on-chip photonic circuits rather bulky. Furthermore, a fundamental incompatibility arises between photonics and nanometer-scale electronics because light breaks free when confined to sizes below its wavelength. Instead, coupling light to the free electrons of metals can lead to quasiparticles called plasmons with nanometer-scale mode volumes. Surface Plasmon Polaritons (SPP) offer a unique alternative for nanoscale components beyond the fundamental limits of dielectric and semiconductor waveguides, opening a new route to on-chip nanophotonic devices and, in particular, to the building-blocks for quantum computing. Moreover, a new architecture, based on the so called classical Entanglement, is introduced to overcome the KLM scheme. The present proposal of architecture provides the realization of deterministic gates (not affected by “repeat until success” limitation of usual quantum gates), that can be used to build very complex circuits for several applications, such as teleportation, large number factorization (as an example, 56153 with only 4 qubits), Bell state generation. Moreover, the architecture provides the realization of perfect Bell measurements. Net improvements with respect to usual schemes are given by the use of only a single photon or coherent states to run the quantum processing, more robustness under de-coherence, and a faster response.
