Article abstract
Nature Photonics 3, 346 - 350 (2009)
Published online: 24 May 2009 | doi:10.1038/nphoton.2009.93
Subject Category: Quantum optics
Manipulation of multiphoton entanglement in waveguide quantum circuits
Jonathan C. F. Matthews1,3, Alberto Politi1,3, André Stefanov1,2 & Jeremy L. O'Brien1
Abstract
On-chip integrated photonic circuits are crucial to further progress towards quantum technologies and in the science of quantum optics. Here we report precise control of single photon states and multiphoton entanglement directly on-chip. We manipulate the state of path-encoded qubits using integrated optical phase control based on resistive elements, observing an interference contrast of 98.2 
0.3%. We demonstrate integrated quantum metrology by observing interference fringes with two- and four-photon entangled states generated in a waveguide circuit, with respective interference contrasts of 97.2 0.4% and 92 4%, sufficient to beat the standard quantum limit. Finally, we demonstrate a reconfigurable circuit that continuously and accurately tunes the degree of quantum interference, yielding a maximum visibility of 98.2 0.9%. These results open up adaptive and fully reconfigurable photonic quantum circuits not just for single photons, but for all quantum states of light.
- Centre for Quantum Photonics, H. H. Wills Physics Laboratory & Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB, UK
- Present address: Federal Office of Metrology METAS, Lindenweg 50, CH-3003, Bern-Wabern, Switzerland
- These authors contributed equally to this work
Correspondence to: Jeremy L. O'Brien1 e-mail: Jeremy.OBrien@bristol.ac.uk
