Multidimensionally entangled photons travel through single-mode fiber-optic cable

Quantum entanglement has been increasingly touted as a promising way to develop quantum cryptography and communication technology. One popular method entails entangling the polarization states of photon pairs (see the article by Barbara Terhal, Michael Wolf, and Andrew Doherty, Physics Today, April 2003, page 46). Recently, some physicists have developed a higher-dimensional approach that entangles a photon’s spatial modes of light, such as the transverse modes perpendicular to the light’s propagation direction. That approach allows for more information per photon to be transported and may be more resistant to hacking and background noise. But so far, it has required custom-made multimode fiber-optic cable that can accommodate the light’s various spatial modes. Now Jian Wang (Huazhong University of Science and Technology in Wuhan, China), Andrew Forbes (University of the Witwatersrand in Johannesburg, South Africa), and their colleagues have demonstrated that multidimensionally entangled photons can be transported through single-mode fiber.