CE47 - Technologies quantiques

A bright source of Indistinguishable Polarization-entangled On-Demand photon pairs – IPOD

Submission summary

Pairs of entangled, indistinguishable single photons are key resources for quantum communications and optical quantum information processing. For most envisioned applications, it is crucial that these pairs are emitted with controlled timing and high efficiency, which represents a considerable challenge. In IPOD, we propose to realize this long-awaited device with III-V semiconductor technology. Our ambition is to provide the quantum information community with an on-demand source that features game-changing performances: pair emission efficiency >70%, degree of entanglement >80% and degree of indistinguishability >80%. In addition, our source will deliver a Gaussian output beam (mode matching 98.5%), which can be efficiently coupled to a single-mode optical fiber for the distribution of quantum light over long distances. Finally, it will also be spectrally-tunable, so as to enable the future operation of several of these devices at the same wavelength in quantum networks.

Our device exploits the biexciton radiative cascade which takes place in a quantum dot (QD). Starting from the biexciton state (two trapped electron-hole pairs), radiative recombination can follow two parallel paths, via two intermediate excitonic levels. If the energy splitting between these levels - the so-called fine structure splitting (FSS) - is smaller than the radiative linewidth, the cascade generates a pair of photons having entangled polarizations (and different colors). In this project, we will employ self-assembled InAs QDs, which emits in the near infrared (around 900 nm) and display excellent optical properties. To achieve our objective, four major challenges should be overcome: 1) one needs to extract the two detuned photons from the high index matrix which surrounds the QD; 2) QDs generally feature an in-plane asymmetry which leads to a finite FSS and spoils the entanglement; 3) indistinguishable photons can be emitted only if decoherence processes are much slower than photon emission, a significant challenge in the solid-state; 4) since all QDs are different, spectral tunability is a necessary requirement to use this system in a real quantum repeater.

IPOD builds on a new device combining advanced photonic and mechanical engineering. On the photonic side, the QD will be embedded in a tapered nanocavity. This novel photonic structures simultaneously offers large extraction efficiency (>85%) and Purcell spontaneous emission enhancement (x6), over a broad operation bandwidth (30 meV) to collect both photons emitted from the radiative cascade. Purcell acceleration makes photon emission faster that decoherence processes, a key asset to emit indistinguishable photons. In addition, it broadens the radiative linewidths, and thus relaxes the condition on the FSS to achieve a large degree of entanglement. The proposed structure will also deliver a Gaussian output beam.

On the mechanical side, our source will also integrate an actuator designed to apply an anisotropic external stress on the QD, in order to compensate for its natural asymmetry and to enable spectral tuning. Within IPOD, two complementary strategies will be explored. A planar piezo actuator triggered by multiple pairs of electrodes will be integrated directly below the photonic structure. This approach, which offers a full control over the in-plane stress tensor, has never been combined with a photonic structure offering a large collection efficiency. In parallel, we will also explore a radically new approach: the electrostatic bending of a structure covered by an anisotropic shell. Piezo actuation and electrostatic bending will be finally combined to gain a full 3D control over the stress tensor, enabling independent tunability of excitonic and biexcitonic QD transitions.

The success of IPOD will enable new realizations in quantum optics and the concepts developed in this project will be directly transferable to emitters in other spectral ranges (for example in the telecom windows).

Project coordination

Jean-Philippe POIZAT (Institut Néel - CNRS)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


PHELIQS Photonique Electronique et Ingénierie Quantiques
INEEL Institut Néel - CNRS

Help of the ANR 459,630 euros
Beginning and duration of the scientific project: December 2019 - 48 Months

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