Generating, manipulating and measuring entanglement and mixture with a reconfigurable photonic circuit

• Published in: Nature photonics Vol. 6; no. 1; pp. 45 - 49
• Main Authors: Shadbolt, P. J., Verde, M. R., Peruzzo, A., Politi, A., Laing, A., Lobino, M., Matthews, J. C. F., Thompson, M. G., O'Brien, J. L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2012; Nature Publishing Group
• Subjects: 639/624/400/482; Applied and Technical Physics; Circuits; Continuums; Devices; Entangled states; Entanglement; Inequalities; Phase shifters; Photonics; Physics; Physics and Astronomy; Quantum Physics
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/nphoton.2011.283

Entanglement is the quintessential quantum-mechanical phenomenon understood to lie at the heart of future quantum technologies and the subject of fundamental scientific investigations. Mixture, resulting from noise, is often an unwanted result of interaction with an environment, but is also of fundamental interest, and is proposed to play a role in some biological processes. Here, we report an integrated waveguide device that can generate and completely characterize pure two-photon states with any amount of entanglement and arbitrary single-photon states with any amount of mixture. The device consists of a reconfigurable integrated quantum photonic circuit with eight voltage-controlled phase shifters. We demonstrate that, for thousands of randomly chosen configurations, the device performs with high fidelity. We generate maximally and non-maximally entangled states, violate a Bell-type inequality with a continuum of partially entangled states, and demonstrate the generation of arbitrary one-qubit mixed states. Researchers demonstrate a reconfigurable integrated quantum photonic circuit. The device comprises a two-qubit entangling gate, several Hadamard-like gates and eight variable phase shifters. The set-up is used to generate entangled states, violate a Bell-type inequality with a continuum of partially entangled states and demonstrate the generation of arbitrary one-qubit mixed states.