Atomic Physics Seminar: Megan Stanley, Cambridge University, “Phase-tuned entangled state generation between two distant electron spins”

The prerequisite step in assembly of a quantum network for information processing or communication is generation of entanglement between nodes. Photon-mediated protocols in particular afford flexibility to a quantum network, and have been demonstrated in atomic [1] and diamond defect systems [2] and, very recently, using heavy-hole spins in InGaAs quantum dots (QDs) [3]. The strong light-matter coupling in QDs and high photon quality make them an attractive system for rapid entanglement distribution. Here, I will talk about our recent demonstration of electron spin-spin entanglement between QDs separated by several metres, where we find an average Bell-state fidelity of 61.6±2.3% [4]. Using a single-photon detection protocol [5] we report the highest entanglement generation rate thus far of 7.3 kHz. In addition, the two-spin Bell-state phase is fully controllable through the optical phase of a Mach-Zehnder interferometer. Entangled state phase control was only previously achieved for atomic nodes located in the same trap [6]. I will also discuss the particular challenges of working in a dynamic solid-state environment, where both charge noise and an inherent nuclear spin bath can have significant impacts on photon quality and spin coherence [7]. References: [1] Moehring, D.L. et al., 2007, Nature, 449, 68-71; [2] Bernien, H. et al., 2013, Nature, 497, 86-90; [3] Delteil, A. et al., 2016, Nature Phys., 12, 218-223; [4] Stockill, R. et al., 2017, arXiv:1702.03422; [5] Cabrillo, C. et al., 1999 PRA, 59, 1025-1033; [6] Slodička, L. et al., 2013 PRL, 110, 083603; [7] Stanley, M. J. et al., 2014 PRB, 90, 195305