A CMOS silicon spin qubit (1605.07599v1)

Abstract: Silicon, the main constituent of microprocessor chips, is emerging as a promising material for the realization of future quantum processors. Leveraging its well-established complementary metal-oxide-semiconductor (CMOS) technology would be a clear asset to the development of scalable quantum computing architectures and to their co-integration with classical control hardware. Here we report a silicon quantum bit (qubit) device made with an industry-standard fabrication process. The device consists of a two-gate, p-type transistor with an undoped channel. At low temperature, the first gate defines a quantum dot (QD) encoding a hole spin qubit, the second one a QD used for the qubit readout. All electrical, two-axis control of the spin qubit is achieved by applying a phase-tunable microwave modulation to the first gate. Our result opens a viable path to qubit up-scaling through a readily exploitable CMOS platform.

• The paper demonstrates that a CMOS-based silicon spin qubit achieves two-axis electrical control via phase-tunable microwave modulation, reaching Rabi frequencies up to 85 MHz.
• The study details a hole spin qubit in a two-gate p-type transistor, with dephasing times of 60 ns and Hahn echo coherence extending to 245 ns.
• The work highlights how integrating qubit fabrication into CMOS processes accelerates scalability for quantum processors by merging classical and quantum technologies.

Insightful Overview of "A CMOS Silicon Spin Qubit" Paper

In the field of quantum computing, the paper titled "A CMOS Silicon Spin Qubit," authored by Maurand et al., explores the potential of silicon, a dominant material in classical computing, for scalable quantum computing applications. The authors present a quantum bit (qubit) device built using industry-standard CMOS processes, establishing a promising connection between classical and quantum computation technologies.

Core Contributions

The research focuses on a hole spin qubit implemented within a silicon quantum dot (QD) framework. The experimental setup consists of a two-gate p-type transistor with an undoped channel. The first gate is used to form a quantum dot for encoding the spin qubit, while the second gate facilitates qubit readout. A notable breakthrough in this work is the demonstration of two-axis electrical control of the spin qubit, achieved by applying a phase-tunable microwave (MW) modulation to the first gate. The experimental results indicate that the proposed device architecture could be effectively integrated into existing CMOS infrastructures, providing a feasible route for qubit up-scaling.

Numerical Results and Experimental Findings

The authors report significant findings related to the performance of their silicon-based spin qubits:

• Rabi Frequencies: They achieved fast Rabi oscillations with frequencies up to 85 MHz, comparable to the highest values reported for electron-based semiconductor spin qubits.
• Dephasing Times: The inhomogeneous dephasing time $T_2^*$ was measured to be approximately 60 ns, while the Hahn echo coherence time $T_{\text{echo}}$ extended to around 245 ns.
• Gate-Controlled Coherence: Through electric-dipole spin resonance (EDSR), coherent spin rotations were successfully driven by MW modulation, evidenced by characteristic current modulations in source-drain measurements.

Advancements in CMOS Integration

The use of a CMOS platform for qubit fabrication marks a significant step towards the realization of large-scale quantum processors that can coexist with classical hardware. This integrated approach could circumvent complex issues such as device consistency, multilayer wiring, and qubit-to-qubit coupling, which are pivotal for implementing surface-code quantum computing architectures. Moreover, the adaptability of the CMOS process suggests a potential for extensive qubit device scaling using established semiconductor manufacturing techniques.

Theoretical and Practical Implications

Theoretically, the research underscores the potential advantages of silicon spin qubits in terms of coherence times due to weaker hyperfine interactions in silicon, especially when isotopically purified. Practically, the ability to fabricate qubits using industry-standard processes could lead to scalable and economically viable quantum devices, advancing quantum computing towards practical applications.

Future Developments

As silicon spin qubits become better understood, future research should focus on improving the coherence times and exploring single-shot readout techniques for qubit measurement. Additionally, there is a compelling need for developing coupling mechanisms that facilitate qubit interactions while maintaining high fidelity. Continued efforts to benchmark silicon qubits against other qubit implementations will further elucidate the role of silicon in the rapidly evolving landscape of quantum computing.

In conclusion, the research by Maurand et al. presents a significant advancement in the utilization of CMOS processes for the development of silicon spin qubits. This work not only highlights critical experimental achievements but also sets the stage for future innovations that align quantum technologies with classical computing paradigms.