Initialization of neutral and charged exciton spin states in a telecom-emitting quantum dot

Photonic cluster states are highly entangled states that allow for photonic quantum computing and memory-less quantum repeaters. Their generation has been recently demonstrated using semiconductor quantum dots emitting at the 900 nm wavelength range. However, a similar demonstration at the communication-optimal telecom range has remained elusive. A key ingredient that is still missing is an appropriate optical excitation method. A central requirement of such a method is to allow an arbitrary spin initialization of quantum-dot excitonic complexes. In this work, we report on developing such a method based on a quasiresonant 𝑝-shell excitation for an InAs/InGaAs quantum dot emitting at 1535 nm. We show qubit writing of a neutral exciton and spin-preserving excitation of a negative trion. Using the Larmor precession of the negative trion under an externally applied magnetic field, we determine the in-plane 𝑔 factors of both the electron and the hole in the investigated quantum dot. In addition, we measure a lower bound on the hole coherence time, 𝑇$^*_2$ > 6.4ns, boosting its candidacy as a sound photon entangler for more advanced quantum photonic schemes.