Photonic components for Quantum Information science

Abstract

Integrated photonics is required to fully exploit the capabilities of Optical Quantum Information science. We demonstrate new components that take full advantage of the integrated architecture; we show quantum interference in MMI couplers and two-particle quantum walks in coupled waveguides.Quantum information science takes advantage of the fundamental laws of quantum mechanics to perform particular tasks better than the classical counterpart. It promises new paradigms of communication, computation and measurement; such as perfectly secure quantum key distribution, intrinsic parallel computation and increased precision by beating the standard quantum limit. Of the various physical systems being pursued, photons are often the logical choice [1], thanks to their low noise properties, ease of manipulation and transmission. In addition to single photon sources and detectors, photonic quantum technologies will rely on sophisticated optical circuits involving high-visibility classical and quantum interference. Already a number of optical quantum circuits have been realized for quantum metrology, lithography, quantum logic gates, and other entangling circuits. However, these demonstrations have relied on large-scale (bulk) optical elements bolted to large optical tables, thereby making them inherently non-scalable and confining them to the research laboratory. Recently we report the implementation of quantum optic integrated circuits, which not only dramatically reduces the footprint of quantum circuits, but allows unprecedented stability and control of the optical path length; this reveals the possibility for realizing previously unfeasible large scale quantum circuits [2]. We demonstrated silica on silicon circuits that implement key components for quantum information, including CNOT gates [3] and the circuit at the basis of any single-qubit operation [4]. These components show promising progresses toward fault tolerance operation [5]. We also used integrated waveguides to implement a circuit that performs a compiled version of Shor's quantum algorithm [6] to factorize 15. Here we report the demonstration of circuits that extend the capabilities of the components already demonstrated, to take full advantage of the integrated optics architecture.Different techniques can be used to realize beam splitting operations in integrated optics. Multi-mode interference (MMI) splitters are based on the self imaging principle, by which an input field profile is reproduced in single or multiple images at periodic intervals along the propagation direction of a multimode guide [7]. MMI devices allow the design of NxM splitters with superior performances, excellent tolerance to polarization and wavelength variations and relaxed fabrication requirements compared to the other main beam splitting technology, the directional couplers. MMI splitters were designed and fabricated in Silica on Silicon chips. The devices are composed by 2 or 4 single mode waveguides that serve as input and output for the multi-mode section and terminate with a...