Spins in semiconductor quantum dots hold great promise as building blocks of quantum processors. Trapping them in SiMOS transistor-like devices eases future industrial scale fabrication. Among the potentially scalable readout solutions, gate-based dispersive radiofrequency reflectometry only requires the already existing transistor gates to readout a quantum dot state, relieving the need for additional elements. In this effort towards scalability, traveling-wave superconducting parametric amplifiers significantly enhance the readout signal-to-noise ratio (SNR) by reducing the noise below typical cryogenic low-noise amplifiers, while offering a broad amplification band, essential to multiplex the readout of multiple resonators. In this work, we demonstrate a 3GHz gate-based reflectometry readout of electron charge states trapped in quantum dots formed in SiMOS multi-gate devices, with SNR enhanced thanks to a Josephson traveling-wave parametric amplifier (JTWPA). The broad, tunable 2GHz amplification bandwidth combined with more than 10dB ON/OFF SNR improvement of the JTWPA enables frequency and time division multiplexed readout of interdot transitions, and noise performance near the quantum limit. In addition, owing to a design without superconducting loops and with a metallic ground plane, the JTWPA is flux insensitive and shows stable performances up to a magnetic field of 1.2T at the quantum dot device, compatible with standard SiMOS spin qubit experiments.

Charge noise is one of the main sources of environmental decoherence for spin qubits in silicon, presenting a major obstacle in the path towards highly scalable and reproducible qubit fabrication. Here we demonstrate in-depth characterization of the charge noise environment experienced by a quantum dot in a CMOS-fabricated silicon nanowire. We probe the charge noise for different quantum dot configurations, finding that it is possible to tune the charge noise over two orders of magnitude, ranging from 1 ueV^2 to 100 ueV^2. In particular, we show that the top interface and the reservoirs are the main sources of charge noise and their effect can be mitigated by controlling the quantum dot extension. Additionally, we demonstrate a novel method for the measurement of the charge noise experienced by a quantum dot in the few electron regime. We measure a comparatively higher charge noise value of 40 ueV^2 at the first electron, and demonstrate that the charge noise is highly dependent on the electron occupancy of the quantum dot.

We propose and demonstrate complete spin state readout of a two-electron system in a double quantum dot probed by an electrometer. The protocol is based on repetitive single shot measurements using Pauli spin blockade and our ability to tune on fast timescales the detuning and the interdot tunnel coupling between the GHz and sub-Hz regime. A sequence of three distinct manipulations and measurements allows establishing if the spins are in S, Tzero, Tplus or Tminus state. This work points at a procedure to reduce the overhead for spin readout, an important challenge for scaling up spin qubit platforms.

One of the main advantages of silicon spin qubits over other solid-state qubits is their inherent scalability and compatibility with the 300-mm complementary metal oxide semiconductor (CMOS) fabrication technology that is already widely used in the semiconductor industry, while maintaining high readout and gate fidelities. We demonstrate the detection of a single electron spin using energy-selective readout in a CMOS-fabricated nanowire device with an integrated charge detector. We measure a valley splitting of 0.3 meV and 0.16 meV in two similar devices. The anisotropy of the spin-valley mixing is measured and shown to follow the dependence expected from the symmetry of the local confinement, indicating low disorder in the region of the quantum dot. Finally the charge noise in the strong spin-valley coupling regime is investigated and found to induce fluctuations in the qubit energy in the range of 0.6 GHz/ root Hz.

We demonstrate singlet-triplet readout and parity readout allowing to distinguish T0 and the polarized triplet states. We achieve high fidelity spin readout with an average fidelity above $99.9\%$ for a readout time of $20~\mu$s and $99\%$ for $4~\mu$s at a temperature of $0.5~K$. We initialize a singlet state in a single dot with a fidelity higher than $99\%$ and separate the two electrons while keeping the same spin state with $a \approx 95.6\%$ fidelity.

Lecture haute fidélité des spins d'électrons dans les boîtes quantiques silicium mos La découverte et la démonstration d'algorithmes quantiques plus performants que tous les algorithmes classiques ont donné naissance au nouveau domaine de recherche qu'est la technologie de l'information quantique. Depuis l'invention du transistor et la commercialisation des microprocesseurs qui a suivi, le développement des ordinateurs a été guidé par la loi de Moore. Au cours des premières décennies, l'industrie a réussi à tenir ses promesses d'une puissance de calcul plus grande avec chaque nouvelle génération, il semble que la loi de Moore touche lentement à sa fin. La technologie de l'information quantique pourrait offrir une voie vers une croissance continue de la puissance de calcul, non pas par une augmentation du nombre de transistors, mais par un changement de la logique de calcul. Ce changement de paradigme nécessite d'énormes quantités de recherche pour rattraper la technologie moderne. La plupart des estimations donnent une limite inférieure d'un million de qubits physiques pour qu'un processeur quantique soit utile pour résoudre des problèmes du monde réel avec des algorithmes quantiques. Bien que les plus grands processeurs quantiques actuels se composent d'environ 100 qubits, ces derniers sont loin d'être parfaits. Souffrant de différentes erreurs, les processeurs quantiques actuels nécessitent de grandes équipes d'experts pour faire fonctionner. La construction d'un processeur quantique comportant des millions de qubits nécessite une technologie fiable et scalable. Dans ce contexte, les qubits de spin dans les boîtes quantiques semiconductrices constituent une plateforme de qubits intéressante qui pourrait bénéficier des techniques de fabrication à grande échelle de l'industrie moderne des semiconducteurs.La communauté s'accorde largement à dire que les qubits doivent satisfaire aux cinq critères de DiVincenzo pour être considérés pour des processeurs quantiques à grande échelle. La communauté des qubits de spin semiconducteur se concentrait jusqu'à présent sur la démonstration de deux de ces critères, notamment "des temps de décohérence longs et significatifs" et "un ensemble "universel" de portes quantiques". Les résultats exceptionnels ont conduit à recentrer maintenant l'effort sur les autres critères. Nous travaillons sur deux d'entre eux. Nous utilisons un dispositif fabriqué dans un processus FDSOI de 300 mm, promettant l'évolutivité requise par le premier critère de DiVincenzo : "Un système physique évolutif avec un qubit bien caractérisé". Le dispositif consiste en un nanofil de silicium qui relie deux réservoirs. Des grilles, patternées sur le dessus du nanofil, permettent l'accumulation de boîtes quantiques dans les coins du nanofil. Dans notre dispositif, nous créons un système de 2 x 2 boîtes quantiques dans le nanofil. Nous utilisons la réflectométrie rf comme capteur de charge, en utilisant l'un des QD comme capteur. Ensuite, nous utilisons ce dispositif pour réaliser un double boîte quantique. Nous mesurons le blocage de spin de Pauli en utilisant la lecture ST et la lecture de parité, ce qui nous permet de faire la distinction entre le singlet S et les trois états triplets T0, T- et T+ ou entre les états de spin non polarisés S et T0 et les états de spin polarisés T- et T+. Nous démontrons une haute fidélité pour les deux types de lecture. La fidélité de la lecture ST est > 99% à 50 kHz en raison d'une relaxation relativement rapide, la lecture de la parité dépasse 99,9% (99%) à 50 kHz (250 kHz). Ainsi, les deux lectures répondent à la cinquième condition de DiVincenzo : "une capacité de mesure spécifique au qubit". De plus, nous effectuons ces mesures à une température de 0,5 K, ce qui montre la robustesse en température de ce type de lecture. En utilisant ce readout, nous caractérisons le système à deux spins en utilisant des expériences de Landau-Zener et de spin-funnel.

Scalability is one of the biggest advantages of silicon spin qubits over other platforms, making them very promising candidates in the quest for quantum computing. In this work we approach the regime of interest for large-scale qubit integration, showing that we can deliver high electrostatic coupling control and individual tunability over an array of quantum dots (QDs). To do this we use FDSOI devices fabricated with 2-metal gate levels in an industry-compatible CMOS process. We operate them at 100mK, and in a dot-configuration where large control on tunnel barriers is leveraged. In the many-electron regime, we observe the transition of quantum dot array from single- to triple-dot configurations. Moreover, in the few-electron regime, we demonstrate the effective and in-situ modulation of the tunnel coupling between two adjacent QDs.

Spins in gate-defined silicon quantum dots are promising candidates for implementing large-scale quantum computing. To read the spin state of these qubits, the mechanism that has provided the highest fidelity is spin-to-charge conversion via singlet-triplet spin blockade, which can be detected in-situ using gate-based dispersive sensing. In systems with a complex energy spectrum, like silicon quantum dots, accurately identifying when singlet-triplet blockade occurs is hence of major importance for scalable qubit readout. In this work, we present a description of spin blockade physics in a tunnel-coupled silicon double quantum dot defined in the corners of a split-gate transistor. Using gate-based magnetospectroscopy, we report successive steps of spin blockade and spin blockade lifting involving spin states with total spin angular momentum up to $S=3$. More particularly, we report the formation of a hybridized spin quintet state and show triplet-quintet and quintet-septet spin blockade. This enables studies of the quintet relaxation dynamics from which we find $T_1 \sim 4 ~\mu s$. Finally, we develop a quantum capacitance model that can be applied generally to reconstruct the energy spectrum of a double quantum dot including the spin-dependent tunnel couplings and the energy splitting between different spin manifolds. Our results open for the possibility of using Si CMOS quantum dots as a tuneable platform for studying high-spin systems.

We discuss the status, challenges and perspectives of "Quantum CAD" for the design and exploration of spin qubits. We highlight the similarities and differences with conventional TCAD for micro-electronics, and focus on design, physics and variability of silicon-on-insulator qubits as an illustration.

The recent development of arrays of quantum dots in semiconductor nanostructures highlights the progress of quantum devices toward large scale. However, how to realize such arrays on a scalable platform such as silicon is still an open question. One of the main challenge resides in the detection of charges within the array. It is a prerequisite functionality to initialize a desired charge state and readout spins through spin-to-charge conversion mechanisms. In this paper, we use two methods based on either a single-lead charge detector, or a reprogrammable single electron transistor. Thanks to these methods, we study the charge dynamics and sensitivity by performing single shot detection of the charge. Finally, we can probe the charge stability at any node of a linear array and assess the Coulomb disorder in the structure. We find an electrochemical potential fluctuation induced by charge noise comparable to that reported in other silicon quantum dots.

We report the efforts, challenges and perspectives dedicated towards building a reliable spin read-out for Si spin qubit systems. We review several strategies that are pursued in the semiconductor quantum circuit community. We discuss their pros and cons with respect to their performance (speed and fidelity), their integration potential and their footprint. We then address the envisioned architecture to read-out spin qubits at large scale.

We fabricated linear arrangements of multiple split-gate devices along an SOI mesa, thus forming a 2×N array of individually controllable Si quantum dots (QDs) with nearest neighbor coupling. We implemented two different gate reflectometry-based readout schemes to either probe spin-dependent charge movements by a coupled electrometer with single-shot precision, or directly sense a spin-dependent quantum capacitance. These results bear significance for fast, high-fidelity single-shot readout of large arrays of foundry-compatible Si MOS spin qubits.

The engineering of a compact qubit unit cell that embeds all quantum functionalities is mandatory for large-scale integration. In addition, these functionalities should present the lowest error rate possible to successfully implement quantum error correction protocols(1). Electron spins in silicon quantum dots are particularly promising because of their high control fidelity(2-5) and their potential compatibility with complementary metal-oxide-semiconductor industrial platforms(6,7). However, an efficient and scalable spin readout scheme is still missing. Here we demonstrate a high fidelity and robust spin readout based on gate reflectometry in a complementary metal-oxide-semiconductor device that consists of a qubit dot and an ancillary dot coupled to an electron reservoir. This scalable method allows us to read out a spin in a single-shot manner with an average fidelity above 98% for a 0.5 ms integration time. To achieve such a fidelity, we combine radio-frequency gate reflectometry with a latched spin blockade mechanism that requires electron exchange between the ancillary dot and the reservoir. We show that the demonstrated high readout fidelity is fully preserved up to 0.5 K. This result holds particular relevance for the future cointegration of spin qubits and classical control electronics.