Scaling Quantum-Dot-Qubit Systems

Rubaya Absar

Future quantum processors intend to operate on millions of qubits and Silicon Metal Oxide Semiconductor (MOS) Quantum Dot qubits are a good fit for such a large-scale system due to their compactness in size and large coherence time. To control the operations of the qubits in such a large-scale system, efficient and careful design of the control circuits is very challenging. Here, in this thesis a control circuit is designed for silicon MOS quantum dot qubits operating on a node/ network architecture. Rather than using a 2D array of quantum dots, a node/ network architecture provides enough space for the wiring of integrated control circuits. The control circuit designed here is expected to work on millikelvin (mK) temperature and number of control lines from the mK temperature to 1-4 K temperature, where the digital control systems are operated, is reduced significantly compared to the number of qubits. The reduction in number of control lines from mK temperature is one of the basic requirements while scaling up. All these control circuits operate on the quantum dots based on the assumption that, all the dots are at same potential throughout the network. In practice due to fabrication variations and connection differences the potential of quantum dots varies from qubit to qubit. To solve this problem and pre-tune all the quantum dots to same potential prior to the operation of control circuit, a device level error correcting scheme is introduced and verified by simulation in this thesis.

Mark G. Friesen

Shun-Li Jiang, Tian-Yi Jiang, Yong-Qiang Xu +8 more

Abstract Scaling up spin qubits in silicon-based quantum dots is one of the pivotal challenges in achieving large-scale semiconductor quantum computation. To satisfy the connectivity requirements and reduce the lithographic complexity, utilizing the qubit array structure and the circuit quantum electrodynamics (cQED) architecture together is expected to be a feasible scaling scheme. A triple-quantum dot (TQD) coupled with a superconducting resonator is regarded as a basic cell to demonstrate this extension scheme. In this article, we investigate a system consisting of a silicon TQD and a high-impedance TiN coplanar waveguide (CPW) resonator. The TQD can couple to the resonator via the right double-quantum dot (RDQD), which reaches the strong coupling regime with a charge–photon coupling strength of g 0/(2π) = 175 MHz. Moreover, we illustrate the high tunability of the TQD through the characterization of stability diagrams, quadruple points (QPs), and the quantum cellular automata (QCA) process. Our results contribute to fostering the exploration of silicon-based qubit integration.

Nizar Messaoudi, Azfar Badaroudine, Larissa Njejimana +3 more

Thomas Van Caekenberghe, Paul Steinacker, Bart Raes +31 more

The realization of large-scale silicon quantum processors requires spin qubits compatible with advanced semiconductor manufacturing technologies, demanding lithographic processes that combine nanometer-scale precision with exceptional uniformity. Although the highest-performing silicon spin qubits demonstrated to date have relied on electron-beam (e-beam) lithography, its serial exposure process limits reproducibility studies and wafer-scale fabrication. Here, we demonstrate high-performance silicon metal-oxide-semiconductor (SiMOS) spin qubits fabricated using extreme-ultraviolet (EUV) lithography in a 300 mm semiconductor pilot line. We report wafer-scale quantum-dot uniformity metrics, including 100 % room-temperature gate-to-gate leakage yield and sub-nanometer control of critical gate dimensions. We characterize four double-dot systems realized in two triple-quantum-dot devices. Gate set tomography (GST) reveals consistently high fidelities across all four systems, with values up to 99.8 % for SPAM, 99.9 % for single-qubit gates, and 99.1 % for two-qubit gates. The devices exhibit highly reproducible exchange turn-on characteristics of 10-13 dec/V, indicating high fabrication uniformity enabled by EUV patterning. These results establish EUV lithography as a viable manufacturing technology for quantum processors based on high-fidelity SiMOS spin qubits.

K. Berrada