1. Demonstration of Two-Plasmon Quantum Interference Hyunseok Lee 1

2. ■ Overview Background Recap Surface Plasmon Two Photon Quantum Interference Experiment Procedure Schematic Theoretical analysis Waveguide Design Result & Conclusion Measurement Conclusion Future research Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research 2

3. ■ Surface Plasmon Electronic-optical excitations Strongly interact with environment Decoherence question unsettled Test of indistinguishability! Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research 3

4. Plasmonic TPQI ■ Two Photon Quantum Interference Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Represent the electric fields of the modes by annihilation operators: Represent the action of the beam splitter by an operator with two assumptions: Then the final state of the system given one photon in each input follows: Detectors placed at the outputs will never click simultaneously! 4

5. ■ Schematic (1) Laser -> SPDC -> single photon pairs Waveguide -> converted to plasmon -> TPQI Back to photon -> detectors Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research 5

6. ■ Schematic (2) Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research * C. Hong, Z. Ou, L. Mandel, Phys. Rev. Lett. 59, 2044-2046 (1987). Dielectric case Challenge: Plasmonic waveguide Theory Simulation Fabrication 6

7. ■ TPQI in a Lossy Coupler (1) Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Supermodes 7

8. ■ TPQI in a Lossy Coupler (2) Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research *S. Barnett, J. Jeffers, A. Gatti, R. Loudon, Phys. Rev. A. 57, 2134(1998) Coincidence Rate Delay Ideal TPQI with loss 8

9. ■ Simulation Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research 9

10. ■ Waveguide Design (1) Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research DLSPPW design Optimized dimension & material * R. Briggs, J. Grandidier, S. Burgos, E. Feigenbaum, H. A. Atwater, Nano Lett. 2010, 10(12) 10

11. ■ Waveguide Design (2) Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Dielectric waveguide for comparison S-bends prevent stray light background 11

12. 94.4+/-0.3% 0.12+/-0.01 ps ■ Measurement Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Plasmonic TPQI is clearly shown 93.2+/-1.0% 0.11+/-0.01 ps Plasmonic TPQIPhotonic TPQI 12

13. ■ Conclusion Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Successfully demonstrated unambiguous quantum interference in plasmonic waveguides Close correspondence between dielectric and plasmonic Identical photons remain indistinguishable High degree of coherence Application in quantum computing if loss can be mitigated. 13

14. ■ Future Research Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Further study of plasmon Dispersive regime Extending the technology Integrated quantum photonics 14

15. ■ Acknowledgements Plasmonic TPQI Recap Surface Plasmon TPQI Procedure Schematic Theory Waveguide Design Result Conclusion Future research Air Force Office of Scientific Research Kavli Nanoscience Institute Further reading: J. S. Fakonas, H. Lee, Y. A. Kelaita, H. A. Atwater, Nat. Photonics 8, 317–320 (2014). Thank you for listening! 15