Abstract
Producing advanced quantum states of light is a priority in quantum information technologies. In this context, experimental realizations of multipartite photon states would enable improved tests of the foundations of quantum mechanics as well as implementations of complex quantum optical networks and protocols. It is favourable to directly generate these states using solid state systems, for simpler handling and the promise of reversible transfer of quantum information between stationary and flying qubits. Here we use the ground states of two optically active coupled quantum dots to directly produce photon triplets. The formation of a triexciton in these ground states leads to a triple cascade recombination and sequential emission of three photons with strong correlations. We record 65.62 photon triplets per minute under continuous-wave pumping, surpassing rates of earlier reported sources. Our structure and data pave the way towards implementing multipartite photon entanglement and multi-qubit readout schemes in solid state devices.
Highlights
Producing advanced quantum states of light is a priority in quantum information technologies
In order to generate multipartite correlated photons, most schemes based on spontaneous parametric down conversion (SPDC) use the interference of photon pairs created by independent Poissonian sources and post-select the favoured subset of output photon states[7,10,12,13,14], which significantly adds to the probabilistic nature of the process and the uncorrelated background light
Considering the low arsenic concentration (0.15oxo0.25) of the dot segments, a thinner spacing would lift the barrier and aid the delocalization of electrons, or would promote the directional nonresonant tunnelling in the QDM27, whereas a larger spacing would impair the electron hybridization and interdot coupling
Summary
Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on creating single photons and entangled photon pairs, multipartite correlated photon states are usually produced in purely optical systems by postselection techniques or cascading, with extremely low efficiency and exponentially poor scaling[5,6,7]. The ground state of a single quantum dot hosts at most two bright excitons[15], a biexciton, which can be controlled coherently[16] to produce correlated photon pairs in a so-called cascade recombination process. A realization of photon triplets from a triexciton forming in a QDM serves as an elementary step for the direct generation of multiphoton entanglement, which has so far been limited to photon pairs in solid state systems[23]
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