Mos-based Quantum Information Technology
This project is positioned in the most forefront area of Information and Communication Technology, where new computing paradigms are targeted. Here we deal with the revolutionary concept of quantum computation. We propose to take one of the most promising approaches to quantum computing and implement it onto an industrial CMOS platform. Within the three-year timeframe of this project, we can accomplish the first important step of this implementation: the realisation of the first CMOS-based qubit, the basic building block of a quantum computer. To this aim, we shall take advantage of a state-of-the-art silicon-on-insulator technology available at the 300-mm CMOS platform of CEA-LETI.
A qubit device embeds a quantum two-level system encoding an elementary bit of quantum information. Our type of qubit relies on a spin degree of freedom of either electronic or nuclear nature. It was recently shown that a spin in silicon can hold a bit of quantum information for very long times. This makes it an attractive option for the realisation of a quantum computer. A variety of spin qubits in silicon have already been proposed and experimentally demonstrated in academic research laboratories. The central aim of this project is to show that such high-fidelity spin qubits can be manufactured in silicon using industry-standard CMOS processes within a large-scale nanofabrication facility. Our approach is based one a single, versatile building block, which can be tuned to operate in different regimes giving up to five different qubit realisations in one device. The performance of these different qubit will be benchmarked against key criteria such as fidelity, speed and suitability for large-scale integration.
Design and modelling will be used alongside measured performance metrics to identify optimal large-scale architectures, while control tools will be developed which can be applied to scaled qubit arrays. In addition, we shall develop a toolkit of CMOS-based, classical devices (low-noise amplifiers, rf generators and multiplexers) to be used as low-temperature peripheral electronics for improved qubit control and readout. By sharing the same CMOS technology, qubits and peripheral electronics could even lie close to each other on the same chip. This unique opportunity could be particularly helpful in the development of fast readout circuitry.
SiAM -Silicon at the Atomic and Molecular scale
SiAM aims at exploiting in future ICT devices and circuits the atomic nature of dopants used throughout microelectronics. The key idea is to use the very sharp, deep and reproducible potential created by a dopant in a semiconductor host crystal. Despite its small size (on the scale of the Bohr radius), the donor state of a single dopant can be addressed with conventional lithography techniques, and is therefore perfectly suitable for realistic devices exploiting the quantum nature of single atoms.
The project relies on:
- The extremely mature silicon technology in which, however, no quantum mechanical or atomic properties are at play when dopant atoms are used.
- The very atomic nature of these dopants
The consortium will investigate dopants:
- At the device level, with the demonstration of atomic devices (single dopant) and molecular devices (coupled dopants). A crucial effort towards integration of deterministic implantation in CMOS technology will be made.
- In the theoretical understanding, for exploiting the specific features of dopant-based devices, especially time-dependent processes.
- At the system level, with circuits exploiting the atomic characteristics of dopant based devices.
The consortium brings together three methods for fabricating single-atom transistors: top-down silicon fabrication, bottom-up growth of nanowires and Scanning Tunneling Microscope (STM)-assisted fabrication. This is a unique combination of expertises only available in Europe. In addition, metrology and theory experts will exploit time-dependent phenomena in atomic devices for applications such as electron pumps. Another opportunity is to address directly the spin of a single dopant and make use of its extremely long coherence time to make a single atom quantum bit, crucial for applications in spintronics and quantum computation.
Dopant-based devices: (i) atomically-precise dopant junctions realized with STM-assisted hydrogen resist lithography, (ii) single-atom transistors and pumps made in a silicon foundry and (iii) single atom spin quantum bit made in bottom-up silicon nanowires. Time-dependent theory: the apparent limitation of non-adiabaticity will be turned into an advantage by exploiting the dynamical delays due to non-adiabaticity for robust single-gate operation. Integration of the dopant-based CMOS devices in a circuit will be realized. STM-assisted lithography will be performed on silicon-on-insulator wafers with special surface preparation and capping, in order to avoid the usual surface preparation at very high temperature. Finally, the development of nanovias will pave the way for reintegration of STM defined donor device chips into a CMOS flowchart.
The TOLOP project comprises investigations into three of the levels necessary for a paradigm shift in low-power electronics:
- Fabrication and measurement of devices which are inherently low-power in switching operation at room temperature
- Theory of specific device implementations for each of those technologies to explain and validate the principles behind their low-power capabilities
- Design of architecture to enable the circuit operation of these technologies for overall low-power circuit operation
In each case there will be an investigation of the inherent losses at realistic switching rates, and estimations of the device-circuit-operation trade-offs for minimising energy consumption. Metrics such as the energy-delay product will be provided for each implementation and benchmarked against existing commercial and research technologies.
- Novel single-atom, single-electron and spintronic devices will be investigated experimentally. In the first two cases, the structures are inherently CMOS-compatible whilst in the third a higher-risk approach will be taken whilst still addressing manufacturability
- Both non-Boolean implementations such as multi-valued logic and parallel logic, and optimised Boolean logic implementations will be addressed. Non Boolean logic has the potential for exponential improvement in power needs
- Architectures and operating protocols will be designed to optimise the total power consumption of a circuit-level implementation, taking into account measured and estimated losses at realistic operating rates and temperatures
Device-level proof of concept will be achieved experimentally, driving the design of specific temperaturess.implementations, with theoretical investigation of viability in a realistic circuit environmentrates
Engineering electronic quantum coherence and correlations in hybrid nanostructures
Nanoelectronic devices are foreseen to play a significant impact on next-generation technologies. Simultaneously, they can provide versatile and relatively simple systems to study complex quantum phenomena under well-controlled, adjustable conditions. Existing technologies enable the fabrication of nanostructures (so-called artificial atoms) in which it is possible to add or remove individual electrons, turn on and off interactions, tune the electronic state of a confined system, simply by changing a gate voltage or an external magnetic field.
This project aims at developing metal-semiconductor nanodevices based on semiconductor nanocrystals coupled to different types of electrodes including normal metals, superconductors and ferromagnets. Through low- temperature magnetotransport experiments we investigate the electronic properties of these hybrid nanosystems with an emphasis on the interplay between spin-related effects (e.g. spin- orbit coupling) and strong electronic correlations (Coulomb interactions, superconductivity, ferromagnetism, etc.). We explore various strategies to realize spin-valve and spin-transistor nanodevices. High-frequency, pump-probe electrical measurements are employed to perform coherent spin manipulation and determine the characteristic time scales for spin dynamics. In the case of Si-based nanocrystals, a direct measurement of these time scales, expected to be particularly long, may open new promising routes towards spin-based quantum computation.
Helical states and Majorana fermions in topological nanostructures
The mathematical concept of topology applied to condensed matter has been very helpful to understand the transport properties of certain materials. This description was responsible for the discovery of new states of matter called topological insulators. These are insulating in the bulk of the material, but conducting at the edge. Their band structure is dominated by the spin-orbit interaction and is characterized by one or more topological invariants that distinguish them from traditional insulators. In two dimensions, they give rise to the quantum spin Hall effect and spin states are characterized by helical one-dimensional spin-polarized edge channels. The emergence of these new states of matter is a fundamental topic, but because of their spin properties, they could also have implications in spintronics.
Similar concepts have led to the superconducting counterpart of topological insulators: topological superconductors. The topological character manifest itself in the excitation spectrum of the superconducting state and gives rise to quasiparticles analog to Majorana fermions. Majorana particle is known to be its own antiparticle, have no charge or spin and are therefore very well isolated from the environment and are ideal for storing quantum information. The existence of Majorana fermions was predicted and intensely studied in particle physics but this quest was unsuccessful. The experimental realization of topological superconductivity in superconductor-semiconductor hybrid structures allowed to reproduce the experimental conditions for the creation of Majorana fermions and the first experimental signatures in transport was obtained recently. Since then, the search around the Majorana fermions has become a major theme in condensed matter physics. However, most of these theoretical predictions about these excitations have not received any experimental confirmations.
Our consortium (CEA-INAC and CNRS-Néel in Grenoble, CNRS-IEMN in Lille, and Pittsburg University in US) gathers strong expertise in the fields of topological superconductivity, semiconductor-superconductor hybrid structures and growth of materials with strong spin-orbit coupling. We propose initially to optimize the growth of semiconductor systems characterized by a strong spin-orbit coupling and by an ability to form high-transparency contacts to metal electrodes. In particular we are considering nanowires based on germanium (Ge) and quantum wells based of gallium antimonide (GaSb) and indium arsenide (InAs). We intend to highlight clearly and study the helical spin states. In a second step, we will use these developments to integrate these components in nanoelectronic superconductor-semiconductor hybrid circuits. The expected high quality of the semiconductor structures developed in our consortium will then allow us to demonstrate the unique properties of Majorana fermion excitations, predicted theoretically but remained so far elusive to experimental investigation.