EPOQUES

Exciton-Polariton Optoelectronic and Quantum Employment in Semiconductors

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 Obiettivo del progetto (Objective)

'Both electrons and photons have emerged as essential particles in our information age. Electrons interact strongly with each other and form the basis for computational architectures, while photons interact weakly and are the ideal candidates for communication. While the strength of each particle can also be viewed as a weakness, an emerging research field has focused on the fundamental physics of hybrid particles between electrons and photons. Known as exciton-polaritons, such particles can be generated in solid-state nanostructures such as semiconductor microcavites. Naturally, exciton-polaritons exhibit a mix of properties of electrons and photons and recent fundamental studies have revealed their Bose-Einstein condensation, superfluidity and a rich spin dynamics.

With a range of basic physical effects now known, the potential for constructing devices from these hybrid particles has appeared, yet remains largely unstudied. Optical or electrical spin control of exciton-polaritons has a perspective for information processing, where the strong non-linear interactions between excitons could be sufficient for a complete logical functionality. Going beyond classical effects, exciton-polaritons are quantum particles and seem to be realistic candidates for quantum information processing. Unfortunately the field of exciton-polariton physics has evolved rather separately from the field of quantum information science, likely due to the difficulty in applying the most basic ideas of quantum information theory to exciton-polaritons. Namely, it is not known how to isolate exciton-polaritons as qubits (since they are bosons) such that more advanced schemes based on continuous variables are required.

The aim of this project is to design and study theoretically exciton-polariton based devices. To understand the promise and limitations of these particles an interdisciplinary project between condensed matter physics, quantum optics and quantum information theory is essential.'

Descrizione progetto (Article)

The excitonic part of polaritons allows them to interact strongly with their surroundings, giving rise to nonlinear phenomena enjoyed by electrons. On the other hand, their photonic part restricts the recovery of classical behaviour, allowing them to carry information with minimal data loss.

As well as being of great scientific interest, polaritons have the potential to realise optoelectronic devices, exploiting collective quantum effects at room temperature. The new field of polaritonics is emerging as a highly promising alternative to purely photonic and electronic devices.

The EU-funded project 'Exciton-polariton optoelectronic and quantum employment in semiconductors' (EPOQUES) focused on polariton phenomena in quantum wells and polariton condensates. Significant advances have been made in both directions during the project's two-year lifetime.

EPOQUES scientists developed a new approach for the spatial modulation of light exploiting the interactions between excitons confined in a layered semiconductor structure. By varying excitons' energies with small electric fields, the intensity and phase of reflected light could be controlled. This new approach could provide the basis for holographic arrays.

Furthermore, EPOQUES scientists obtained a better understanding of phenomena caused by spin-orbit coupling in a coherent gas of so-called indirect excitons. In particular, they explored spin transport in excitons formed in quantum wells with a view to designing advanced spintronic devices, relying on the long lifetimes of these quasiparticles.

Research on the polariton condensates concentrated on the transport of particles over macroscopic distances and the increase in the intensity of the condensate as this travels.

The list of EPOQUES project results was not limited to the practical use of polaritons as basic ingredients of optical amplifiers and logical circuits. A series of theoretical tools was developed to describe interactions between polaritons, presented in scientific papers published in peer-reviewed journals.

EPOQUES outcomes are of interest to the academic community as well as industrial research laboratories, and at the same time help to keep Europe's world lead in the field.