Quantum Optics Colloquium by Dapeng Ding

Spin physics in nanophotonic waveguides 

Self-assembled semiconductor quantum dots are excellent single-photon sources with unprecedented quantum efficiency, brightness and indistinguishability [1]. By charging the quantum dot with a single electron, the spin states of the electron can be entangled with the photon states [2]. Further in this way, multi-photon states such as cluster state can be generated from the quantum dot [3]. In this colloquium, I will present our recent results on quantum coherence and state control of an electron spin in a quantum dot embedded in a nano-beam waveguide by using coherent population trapping and Ramsey interference. The waveguide provides near-unity collection efficiency of the emitted photons, but it modifies the transition polarizations in the far field, which is crucial for the quantum state manipulation. Nuclear spins in the quantum dot can be partially polarized by the electron spin and the resulting equivalent magnetic field shifts the Zeeman splitting of the electron spin. I will explain our unique approaches to these two issues in order to successfully observe coherent population trapping and Ramsey interference. 

[1] Interfacing single photons and single quantum dots with photonic nanostructures, Peter Lodahl, Sahand Mahmoodian, and Søren Stobbe, Rev. Mod. Phys. 87, 347 (2015). 

[2] Observation of entanglement between a quantum dot spin and a single photon, W. B. Gao, P. Fallahi, E. Togan, J. Miguel-Sanchez and A. Imamoglu, Nature 491, 426 (2012). 

[3] Proposal for Pulsed On-Demand Sources of Photonic Cluster State Strings, Netanel H. Lindner and Terry Rudolph, Phys. Rev. Lett. 103, 113602 (2009).