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Published online: 7 July 2010 | doi:10.1038/nchina.2010.85

Quantum physics: Entanglement for sure

Felix Cheung

Introduction

© (2010) Nature Photonics

Entangled photon pairs are great information carriers for quantum communication and quantum computation. Unfortunately, spontaneous parametric down-conversion (SPDC) — the predominant mechanism for generating entangled photon pairs — is a random process and therefore has difficulty in supporting practical applications. Jianwei Pan and Kai Chen at the University of Science and Technology of China in Hefei and co-workers¹ have now overcome this limitation by designing a set-up for deterministically producing entangled photon pairs (that is, with a probability of 100%).

The set-up (see image) comprises an SPDC source for producing entangled photon pairs, an optical circuit of beamsplitters for splitting the photons, and six outputs. Single-photon detectors monitor four of the outputs and function as triggers — the detection of four photon states signals the creation of one entangled photon pair through the other two outputs.

The use of an SPDC source makes the entangled photon pairs stable and robust. The researchers say that they could also improve the performance of their set-up by using beamsplitters with different transmission ratios. So far, they have achieved a fidelity of 87% and a state-preparation efficiency of 45%. The next step in their study is to miniaturize the SPDC source and optical circuit using waveguides instead of bulk optics for on-chip integration.

The authors of this work are from:
Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany; Department of Physics and National Center for Theoretical Sciences, National Cheng Kung University, Tainan, Taiwan; Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, China.

Reference

1. Wagenknecht, C. et al. Experimental demonstration of a heralded entanglement source. Nature Photon. doi:10.1038/nphoton.2010.123 (2010). | Article | OpenURL