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EXQUISITE Report Summary

Project ID: 615613
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - EXQUISITE (External Quantum Control of Photonic Semiconductor Nanostructures)

The EXQUISITE project explores the external quantum control of photonic semiconductor nanostructures. The research establishes a new field of science and technology settled at the crossroads between nonlinear dynamics, nanophotonics and quantum information processing. Particular focus is on the non-classical regime of external control where quantum fluctuations govern the nonlinear dynamics of feedback coupling, optical injection, chaos and synchronization. In order to address this regime, the EXQUISITE team is using quantum dot microcavities, which take advantage of cavity quantum electrodynamics (cQED) effects. These structures allow for laser operation based on only a few quantum emitters and very low laser threshold powers.

The research in this project comprises technological, experimental and theoretical aspects of external quantum control of nanophotonic systems. Technological aspects include the deterministic fabrication of quantum dot microcavities with a well-defined number of about 1-20 site-controlled quantum emitters spatially aligned to the antinode of the laser mode. This technological break-through ensures optimum coupling of the small ensemble of emitters to the lasing mode, which is the basis for the exploration of external control and non-linear dynamics in the quantum regime of few-photon – few-emitter interaction.

EXQUISITE focuses on controlling the emission features of nanophotonic systems by optical injection, time-delayed optical feedback and by their mutual coupling. These studies have in common that they aim at pushing the external optical control to its quantum limit, where for instance single photons back couple into the optical mode of a microcavity. This specific and so far unexplored regime of non-linear dynamics is highly attractive as it connects classical and quantum physics to answer important questions appearing in the transition region between the two limiting cases. For instance, via the mutual coupling of microlasers based on a few quantum dots (QDs) as active material we will address how synchronization of chaotic classical oscillators transforms into entanglement of optically coupled quantum emitters.

In the first part of the project, the team members have studied intrinsic instabilities of quantum dot micropillar lasers subject to time delayed feedback and optical injection at ultra-low light levels down to the nanowatt regime. These studies reveal that the dynamics of such lasers is governed by intrinsic instabilities leading to abnormally high bunching (super-thermal photon bunching) in their photon statistics. The associated intensity fluctuations are enforced by few-QD gain competition and by cQED enhanced spontaneous emission noise in the microlasers. cQED effects also lead to novel effects under optical injection, where emission of QD-microlasers is only partially locked to that of the master laser – in contrast to full locking in the classical regime.

Moving further into the realm of quantum optics, EXQUISITE investigates important problems like pushing semiconductor lasers towards the ultimate thresholdless single-quantum dot laser, and external control of two-level emitters while varying the photon statistics of the driving field. Approaching the low-light limit optical injection in a coherently coupled QD – microcavity system, we revealed signatures of injection pulling of single QD emission lines, which is considered as the quantum optical pendant of injection locking.

The research performed in this project has uncovered already a number of intriguing phenomena at the crossroads between classical and quantum physics. Based on the gained technological, experimental and conceptual experience we will progress further to the quantum regime of external optical control. Particularly interesting is the control and mutual coupling of nanophotonic systems via non-classical light fields which will be at the focus of the second part of EXQUISITE.

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