The technology choice in the eco-design of AI architectures
Electronic systems have a significant environmental impact in terms of resource consumption, greenhouse gas emissions and electronic waste, all of which are experiencing a massive upward trend. A large part of the impact is due to production, and more particularly the manufacturing of integrated circuits, which is becoming more and more complex, energy-intensive and resource-intensive with new technological nodes. The technology used for the implementation of a circuit has direct effects on the environmental costs for production and use, the lifespan of the circuit and the possibilities of several life cycles in a circular economy perspective. The technological choice therefore becomes an essential step in the ecodesign phase of a circuit.
The thesis aims to integrate the exploration of different technologies into an eco-design flow of integreted circuit. The purpose of the work is to define a methodology for a systematic integration of the technological choice into the flow, with identification of the best configuration of the architecture implemented for maximizing the lifespan and taking into account the strategies of circular economy. The architectures targeted by the thesis fall into the field of embedded AI, which is experiencing an upward deployment trend and involves major societal challenges. The thesis will constitute a first step in research towards sustainable embedded AI.
Development of integrated superconducting nanowire single photon detectors on silicon for photonic quantum computing
The development of quantum technologies represents a major challenge for the future of our society, in particular to build unhackable communications as well as quantum computers offering computing power well beyond that available with current supercomputers. Photonic quantum bits (or qubits), in the form of single photons, are robust against quantum decoherence and are therefore very attractive for these applications. At CEA-LETI, we are developping an integrated quantum photonics technology on silicon wafers, compatible with industrialization, comprising key building blocks for qubit generation, manipulation and detection on-chip.
The PhD project will be focused on the development of integrated superconducting nanowire single photon detectors, sensitive to the presence of a single photon, required for photonic quantum computing. The objective will be the design of superconducting single photon detectors integrated with ultra-low loss waveguides used for the core of the quantum computing processor, the development of a clean room fabrication process compatible with the existing silicon photonics platform and the characterization of the detector figures of merit (detection efficiency, dark count rate, timing performances) using attenuated lasers. The final goal of the PhD will be the integration of small circuits including several detectors on-chip to characterize the purity and indistinguishability of single photons emitted by a quantum dot source developped in parallel at CEA-IRIG (also located in Grenoble).
This PhD work will be carried out in collaboration between CEA-LETI and CEA-IRIG and will be a strategic cornerstone at the heart of future generations of quantum photonic processors featuring several tens of qubits.
Quantum device integration on Ge/SiGe heterostructures
Spin qubits in semiconductors quantum dots offer a fast scaling perspective of quantum processors by leveraging the manufacturing techniques of the microelectronics industry. To explore this approach, industrial research teams implemented qubits directly on their existing routes (e.g. FDSOI at CEA-Leti or FinFET at Intel). However, these devices suffer from an important electrostatic disorder stemming from the presence of an Si/SiO2 interface next to the qubits.
An alternative way consists in using semiconductor heterostructures based on Ge/SiGe stacks. They allow the charge confinement between crystalline interfaces, thus drastically reducing the electrostatic disorder. Besides the low effective mass of carriers in Ge allows more relaxed dimensions, while the spin-orbit coupling of holes in Ge allows spin manipulations without integration of any external control element.
The PhD thesis aims at developing a Ge/SiGe-based platform at CEA-Leti. The work will consist in fabricating test structures such as Hall bars on different substrate coupons, perform low temperature characterization and provide feedback to help optimizing the substrates quality. In parallel a 200mm route based on eBeam lithography will be set up for the fabrication of one- and two-dimensional arrays of quantum dots.
W color centers for integrated quantum photonics on silicon chips
The integration on a silicon-on-insulator (SOI) chip of all the components necessary for the generation, manipulation and detection of photonic quantum bits is nowadays seen as the most promising route toward scalability for quantum photonic engineering. Until now however, the lack of an “on-demand” source of single photons in silicon has hindered a full exploitation of this strategy.
This PhD project aims to develop such a silicon-based single photon source, integrated into a SOI photonic chip. The source will exploit the spontaneous emission of a single point defect in silicon, the color center W, whose ability to emit single photons has been demonstrated in 2022 by PHELIQS and partners. We will place a single W center at the core of an optical microcavity. Thanks to Purcell-enhancement, a quantum cavity effect, the single photons will all be prepared in the same quantum state, and efficiently funnelled into a waveguide. In order to build such coupled W-cavity systems with a high success rate, we will first develop ordered arrays of isolated W centers by localized ion implantation of SOI wafers. At the end of the project, we will realize a proof-of-principle integrated quantum optics experiment, exploiting W-single photon sources and single photon detectors on the same SOI chip.
The PhD student will be mostly in charge of the study of W centers and cavity effects by advanced optical spectroscopy. He/she will be also involved in technological developments.
Spin-photon coupling and quantum electrodynamics in hybrid semiconducting architectures
Recent years have witnessed a tremendous progress in the development of quantum technologies able to probe and harness quantum degrees of freedom in solid state systems. In this context, the CEA of Grenoble has recently pioneered the demonstration of a hybrid CMOS architecture where a single photon trapped in a superconducting resonator is strongly coupled to the spin of a single hole confined in a double quantum dot [1,2]. This experiment opens important perspectives for the development of novel hybrid circuit Quantum Electrodynamics architectures where the photons can probe, entangle and control the quantum state of distant spins.
The actual potential of such platforms for quantum technologies remains to be assessed from the theoretical side, in particular for applications to quantum computation and simulation. Differently from purely superconducting transmon or flux qubits, the mechanism underpinning strong spin-photon coupling relies on the presence of a significant spin orbit interaction in the valence bands of silicon.
This PhD thesis will reinforce the theoretical activity of the CEA on this topic and will investigate how to optimize readout and manipulation protocols for architectures based on silicon and germanium. Particular effort will be devoted to the quantitative modeling of spin-photon coupling and of the mechanisms limiting the performances of such devices (noise effects). We will also explore the many-body effects emerging when coupling several spins through single or multiple resonators.
 Strong coupling between a photon and a hole spin in silicon, Cécile X. Yu, Simon Zihlmann, José C. Abadillo-Uriel, Vincent P. Michal, Nils Rambal, Heimanu Niebojewski, Thomas Bedecarrats, Maud Vinet, Étienne Dumur, Michele Filippone, Benoit Bertrand, Silvano De Franceschi, Yann-Michel Niquet and Romain Maurand, Nature Nanotechnology 18, 741 (2023)
 Tunable hole spin-photon interaction based on g-matrix modulation, V. P. Michal, J. C. Abadillo-Uriel, S. Zihlmann, R. Maurand, Y.-M. Niquet, and M. Filippone, Phys. Rev. B 107, L041303 (2023)