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Auger recombination is a non-radiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time in the order of microseconds.Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time every quantum event of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a 1 arXiv:1911.04789v2 [cond-mat.mes-hall] 13 Nov 2019Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity; independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process, it also demonstrates the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means.The excitonic transitions in self-assembled quantum dots (QDs) 1,2 realize perfectly a twolevel system in a solid-state environment. These transitions can be used to generate single photon sources 3,4 with high photon indistinguishability, 5,6 an important prerequisite to use quantum dots as building blocks in (optical) quantum information and communication technologies. 7,8 Moreover, self-assembled QDs are still one of the best model systems to study in an artificial atom the carrier dynamics, 9,10 the spin-and angular-momentum properties 11,12 and charge carrier interactions. 13 One important effect of carrier interactions is the Auger process: An electron-hole pair recombines and instead of emitting a photon, the recombination energy is transferred to a third charge carrier, which is then energetically ejected from the QD. 14-17 This is a common effect, mostly studied in colloidal QDs, where it quenches the radiative emission with recombination times in the order of picoseconds to nanoseconds. [18][19][20] This limits the efficiency of optical devices containing QDs like LEDs 21,22 or single photon sources. [23][24][25] In self-assembled QDs, Auger recombination was speculated to be absent, and only recently, it was directly observed in optical measurements on a single self-assembled QD coupled to a charge reservoir with recombination times in the order of microseconds. 26As a single Auger process is a quantum event, it is unpredictable and only the statistical evaluation of many processes gives access to the physical information of the recombination

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The Zeeman-split spin states of a single quantum dot can be used together with its optical trion transitions to form a spin-photon interface between a stationary (the spin) and a flying (the photon) quantum bit. Besides long coherence times of the spin state itself, the limiting decoherence mechanisms of the trion states are of central importance. We investigate here in time-resolved resonance fluorescence the electron and trion dynamics in a single self-assembled quantum dot in an applied magnetic field of up to B = 10 T. The quantum dot is only weakly coupled to an electron reservoir with tunneling rates of about 1 ms −1 . Using this sample structure, we can measure, in addition to the spin-flip rate of the electron and the spin-flip Raman rate of the trion transition, the Auger recombination process, that scatters an Auger electron into the conduction band. The Auger effect destroys the radiative trion transition and leaves the quantum dot empty until an electron tunnels from the reservoir into the dot. The Auger recombination rate decreases by a factor of three from γ A = 3 µs −1 down to 1 µs −1 in an applied magnetic field of 10 T in Faraday geometry. The combination of an Auger recombination event with subsequent electron tunneling from the reservoir can flip the electron spin and thus constitutes a previously unaccounted mechanism that limits spin coherence, an important resource for quantum technologies.