Tip-enhanced Strong Coupling: Broadband Room Temperature Pico-cavity QED with Single Emitters

Optical cavities can enhance and control the light-matter interaction by modifying the local electromagnetic environment of a quantum emitter. However, large cavity mode volumes have prevented strong coupling of single emitters under ambient conditions. We demonstrate tip-enhanced strong coupling (TESC) spectroscopy, imaging, and control based on scanning probe microscopy using plasmonic antenna-tips forming a pico-cavity with the emitter [1]. With single quantum dots we observe room temperature mode splitting up to 160 meV with even sub-nanometer scale mode confinement and atomic precision spatial control [2]. In the extension to the infrared we control molecular vibrations through configurable optical interactions of a nanotip with quantum interference [3] and Purcell enhancement >10⁶ [4]. This work establishes a new paradigm of pico-cavity QED for coherent control of quantum states in solid state emitters and at room temperature. [1] K-D Park et al., Nat. Nanotechnol. 13, 59 (2018). [2] K.-D. Park et al., Science Adv. 5, eaav5931 (2019). [3] E. A. Muller, et al., ACS Photonics 5, 3594 (2018). [4] B. Metzger et al., Phys. Rev. Lett. 123, 153001 (2019).