Spins in InAs quantum dots: qubits, sensors, and photon sources
Over the past few decades a number of exciting applications of quantum coherence and entanglement have been developed that promise fundamental improvements in a variety of areas, including computing, secure communications, and sensing. A team of scientists at the Naval Research Laboratory have been working for many years to develop a physical implementation for these quantum information applications using semiconductor indium arsenide quantum dots QDs). This system has the advantages of a robust solid state host, strong optical transitions, mature device fabrication, tunable properties, and a scalable, monolithic architecture. A single electron or hole spin within a QD acts as a stationary quantum bit that can be optically controlled on a picosecond timescale. In this presentation, I will discuss how a spin in a QD or in a pair of coupled QDs can also be used for sensing mechanical motion and for generating tunable single photons. To sense motion, QDs have been incorporated into mechanical resonators, which couple to the dots through strain. When mechanical resonators are driven, the optical transitions of QDs shift significantly1, and the spin states shift as well. In single QDs, the hole spin shows much stronger coupling to strain than electrons spins, due to the stronger spin-orbit interaction. In coupled QDs, a pair of interacting electron spins can be made highly sensitive to strain gradients that change the relative QD energies. To generate photons, we make use of the Raman spin-flip process2, which has the advantage of generating photons with properties determined by the drive laser and the spin properties. In this way, we are able to demonstrate spectral and temporal control over single photon wavepackets3, with very low two photon emission probability and high indistinguishability.
This work is supported by the U.S. Office of Naval Research and the OSD Quantum Sciences and Engineering Program.
1.Carter, S. G. et al. Sensing flexural motion of a photonic crystal membrane with InGaAs quantum dots. Appl. Phys. Lett.111, 183101 (2017).
2.Sweeney, T. M. et al. Cavity-stimulated Raman emission from a single quantum dot spin. Nat. Photonics8, 442–447 (2014).
3.Pursley, B. C., Carter, S. G., Yakes, M. K., Bracker, A. S. & Gammon, D. Picosecond pulse shaping of single photons using quantum dots. Nat. Commun.9, 115 (2018).