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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - EPPIC (Emitter-mediated Photon-Phonon InteraCtion)

Teaser

Summary

This action, â€œEmitter-mediated Photon-Phonon InteraCtionâ€ (EPPIC), contributes to the research areas of quantum computing and quantum sensors. These are key areas of the quantum technologies flagship initiative, which has the goal of establishing Europe as a leader in the second quantum revolution and its future industrial exploitation. The focus of EPPIC is on III-V semiconductors due to their compatibility with industrial nano-fabrication. Implementing quantum bits in such semiconductors typically relies on the optical control of single spins in local potential traps. These traps are called quantum dots (QDs). In order to carry out computations using QDs their behaviour needs to be well controlled. Continuous interactions with an uncontrolled environment have a disturbing influence on a QD and lead to a phenomenon known as decoherence. Overcoming decoherence is a major challenge in developing quantum technologies. In this project, the aim is to create nano-structures allowing the electrical, optical, and mechanical properties of the QD environment to be controlled. This provides unprecedented control over the possible decoherence processes.

Work performed

In this action, novel opto-mechanical and purely mechanical nanostructures were designed and realized in order to shield QDs from some of the light (optical) and sound (mechanical) modes in their environment. However, before integrating QDs in the designed nanostructures it was of vital importance to control the electrical environment of the QDs. This was accomplished by the design of a diode consisting of an n-i-n-i-p heterostructure, which is compatible with the stringent thickness requirements of the various steps in the nano-fabrication procedure. After this sample was grown by collaborators in Bochum, detailed characterization was carried out showing, for the first time, narrow optical linewidths and spin pumping on charge-tunable QDs in such an ultrathin diode [1]. To test if these excellent QD-properties endure in nano-structured samples, a free-standing beam of gallium-arsenide (3 micrometer x 10 micrometer) was fabricated using optical lithography. After successfully confirming that the narrow linewidths and efficient optical spin pumping could be observed in this structured sample, collaborators in Copenhagen fabricated more advanced photonic nano-structures. A demonstration of spin-controlled photon switching in a nano-beam waveguide was achieved [2]. Following this first demonstration, the nano-structures designed specifically for this action were fabricated. Significant changes had to be made to the experimental setup in Basel to enable a detailed analysis of a QDâ€™s interaction with a well-isolated mechanical mode (â€œresolved sideband regimeâ€). These measurements are currently ongoing.
[1] M. C. LÃ¶bl et al., Physical Review B 96, 165440 (2017)
[2] A. Javadi et al., Nature Nanotechnology 13, 398â€“403 (2018)

Final results

The aim of EPPIC is to demonstrate that nano-structures can manipulate the optical- and spin-dynamics of a QD and that optical control of the QD can be used to manipulate the state of an isolated mechanical resonator. Once the resolved sideband regime has been achieved, the possibility can be revisited of manipulating the spin-dynamics of the QD via the mechanical reservoir. Any of these accomplishments will lay important ground work for future projects: to create non-linear elements for opto-mechanics; to mediate QD-QD interactions by a common mechanical mode; to cool a mechanical resonator to the ground-state via optical control of a single QD; and to use optical control of QDs to prepare non-classical mechanical states. These prospects represent a fascinating vista for the future.