O. Gazzano, S. Michaelis de Vasconcellos, C. Arnold, A. Nowak, E. Galopin, I. Sagnes, L. Lanco, A. Lemaître & P. Senellart
For many applications like long distance quantum communications or for linear quantum computing, the emitted photons need to be indistinguishable. Although quantum dot have been shown to emit indistinguishable photons, combining high brightness and high indistinguishability is not straightforward. Indeed, high brightness requires strong excitation of the system. Thus, many carriers are created in the quantum dot environment leading to pure dephasing.
We have studied the indistinguishability of the single photon source as a function of the source brightness and excitation conditions (figure a). When creating the carriers in the surrounding barriers (green symbols), a high photon indistinguishability (characterized y a mean wavepacket overlap M=0.82) is observed at a source brightness of 30%. When increasing the source brightness, M continuously decreases: additional carriers optically created in the QD surrounding create a fluctuating electrostatic environment.
To circumvent this effect, carriers are directly created in the excited state of the QD (red symbols). Surprisingly, the source indistinguishability is even lower, independently of the source brightness. To combine high brightness with high indistinguishability, we have used a two color excitation scheme (blue symbols): strong pumping directly into an excited QD state together with a weak non-resonant pumping. Doing so, we demonstrate a mean wavepacket overlap as high as 82% for a source brightness of 65%.