What changed
IBM has detailed its research into spin qubits, a new hardware architecture for quantum computing. The company explains how spin qubits encode and manipulate information using the spin states of individual electrons. IBM's HRL Laboratories has been pursuing this approach, which differs from its more mature superconducting transmon qubit architecture.
What this means in practice
IBM's spin qubit research focuses on using quantum dots to trap electrons and control their spin states. The company has developed an exchange-only qubit architecture, recently demonstrating a system with 54 quantum dots configurable to host up to 18 qubits. This system implemented a simple quantum-error-detecting code. Spin qubits must be kept cold in a dilution refrigerator, similar to superconducting qubits.
Spin qubits offer several advantages, including high gate fidelities, compatibility with advanced semiconductor processes, and relatively simple control signals using voltage pulses. These qubits are faster than ion traps or neutral atoms but slower than superconducting qubits in terms of measurement speed.
IBM notes that exchange-only qubits can be controlled with a custom CMOS chip operating at 4 K, reducing the number of necessary connections from room temperature and enabling future system scalability.
Limitations and availability
While spin qubit-based quantum computers currently have fewer qubits than superconducting ones, IBM is working to improve uniformity and fabrication yield. The company also aims to reduce power consumption and consolidate wiring as systems scale. Research is ongoing to address these challenges.
IBM acknowledges that superconducting qubits may reach fault tolerance sooner, with projects like IBM Quantum Starling and Blue Jay. However, the company continues to push forward with spin qubit research to explore their potential for future, larger or less expensive systems. The research is part of IBM's broader effort to bring useful quantum computing to the world.
