Nanophotonic Quantum Phase Switch with a Single Atom

April 22, 2014

a, A single 87Rb atom (blue circle) is trapped in the evanescent field (red) of a photonic crystal (grey). The photonic crystal is attached to a tapered optical fibre (blue), which provides mechanical support and an optical interface to the cavity. The tapered fibre–waveguide interface provides an adiabatic coupling of the fibre mode to the waveguide mode. The inset shows the one-dimensional trapping lattice (green), formed by the interference of a set of optical tweezers and its reflection from the photonic crystal. b, Scanning electron microscope (SEM) image of a single-sided photonic crystal. The pad on the right-hand side is used to tune the cavity resonance thermally by laser heating. [Figure reprinted by permission from Macmillan Publishers Ltd: T. G. Tiecke, J. D. Thompson, N. P. de Leon, L. R. Liu, V. Vuletić, M. D. Lukin, "Nanophotonic Quantum Phase Switch with a Single Atom," Nature, 508, 241–244(10 April 2014) | doi:10.1038/nature13188 ©2014.]

Quantum optical switches are important elements of quantum circuits and quantum networks, analogous to transistors in classical electronic circuits. Operated at the fundamental limit where a single quantum of light or matter controls another field or material system, these switches may enable applications such as long-distance quantum communication, distributed quantum information processing and metrology, and the exploration of novel quantum states of matter. By strongly coupling a photon to a single atom trapped in the near field of a nanoscale photonic crystal cavity, Professor Mikhail Lukin and colleagues from Harvard and MIT devised a system in which a single atom switches the phase of a photon and a single photon modifies the atom’s phase. The scientists experimentally demonstrated an atom-induced optical phase shift that is nonlinear at the two-photon level, a photon number router that separates individual photons and photon pairs into different output modes, and a single-photon switch in which a single 'gate' photon controls the propagation of a subsequent probe field. These techniques pave the way to integrated quantum nanophotonic networks involving multiple atomic nodes connected by guided light. (Read the Letter the researchers published in Nature; read also the Gazette article.)