Friday, May 16, 2008
Beating the channel capacity limit for linear photonic superdense coding
IQC postdoc Tzu-Chieh Wei, together with University of Illinois at Urbana-Champaign collaborators Julio T. Barreiro and Paul G. Kwiat published an article titled "Beating the channel capacity limit for linear photonic superdense coding" in a recent issue of Nature Physics.
Superdense coding harnesses the power of entanglement endowed by quantum mechanics and allows communication of two classical bits by sending only a quantum bit. Photons, traveling at the speed of light, are the natural candidate for performing this task. However, due to some limitation of linear-optics, it turns out the best one can achieve on superdense coding is only 1.58 classical bits per photon ideally.
To overcome this obstacle, ingenious schemes using simultaneous entanglement in multiple degrees offreedom (a.k.a. hyper-entanglement) have been proposed. Barreiro et al. has produced pairs of photons that are hyper-entangled in two degrees of freedom: polarization and orbital angular momentum and have used them to perform one of the new superdense coding schemes. They have broken the conventional linear-optics threshold of 1.58bits per photon.
Their results were in reported in Nature Physics 4, 282 - 286 (01 Apr 2008), doi: 10.1038/nphys919, Letters