Single-shot readout of an electron spin in silicon (1003.2679v3)

Abstract: The size of silicon transistors used in microelectronic devices is shrinking to the level where quantum effects become important. While this presents a significant challenge for the further scaling of microprocessors, it provides the potential for radical innovations in the form of spin-based quantum computers and spintronic devices. An electron spin in Si can represent a well-isolated quantum bit with long coherence times because of the weak spin-orbit coupling and the possibility to eliminate nuclear spins from the bulk crystal. However, the control of single electrons in Si has proved challenging, and has so far hindered the observation and manipulation of a single spin. Here we report the first demonstration of single-shot, time-resolved readout of an electron spin in Si. This has been performed in a device consisting of implanted phosphorus donors coupled to a metal-oxide-semiconductor single-electron transistor - compatible with current microelectronic technology. We observed a spin lifetime approaching 1 second at magnetic fields below 2 T, and achieved spin readout fidelity better than 90%. High-fidelity single-shot spin readout in Si opens the path to the development of a new generation of quantum computing and spintronic devices, built using the most important material in the semiconductor industry.

• The paper achieves the first single-shot readout of an electron spin in silicon using a phosphorus-implanted device coupled with a MOS single-electron transistor.
• It reports a readout fidelity surpassing 90% and a spin relaxation lifetime of nearly 1 second, underscoring the method’s quantum accuracy.
• The integration with conventional silicon technology highlights a scalable route for future quantum computing architectures.

Single-Shot Readout of an Electron Spin in Silicon

The paper "Single-shot readout of an electron spin in silicon" presents a significant advancement in the control and measurement of qubits based on electron spins in silicon, a material extensively used in the semiconductor industry. The authors achieved the first demonstration of single-shot, time-resolved readout of an electron spin in silicon, employing a device comprising implanted phosphorus donors coupled with a metal-oxide-semiconductor (MOS) single-electron transistor (SET). This setup is inherently compatible with existing microelectronics technologies, which is a boon for potential real-world applications.

Technical Summary

The research addresses a pivotal challenge in the field of quantum computing: the reliable readout of quantum bits (qubits) in a single-shot manner. Previous efforts had realized this capability in GaAs/AlGaAs quantum dots but not in the silicon substrate. Silicon is particularly advantageous due to its long coherence times attributed to weak spin-orbit coupling and the capability for isotope purification to eliminate nuclear spins.

In the experiment, the authors fabricated a device using silicon where phosphorus donors create a localized confining potential for electrons. The device also integrates a silicon single-electron transistor that functions as a charge detector. The SET is electrostatically and tunnel-coupled to the spin system, an approach that facilitates the differentiation of spin states via their distinct tunneling behaviors under a strong magnetic field.

Key Results

• Spin Lifetime: A remarkable spin relaxation lifetime approaching 1 second was observed, exceeding the typical limits found in other semiconductors for single-spin measurement.
• Readout Fidelity: The system demonstrated a readout fidelity surpassing 90%, showing precision in identifying the spin state of electrons, a crucial metric for effective quantum computation.
• Magnetic Field and Tunnel-Coupling: The researchers operated at magnetic fields greater than 1 Tesla and an electron temperature of approximately 200 mK to achieve the spin-dependent tunneling necessary for the experiments.

Implications and Future Work

The successful readout of single electron spins in silicon implies the method's integration into silicon-based quantum computing architectures. This work underpins the feasibility of constructing scalable quantum computers using silicon, leveraging existing infrastructure from the semiconductor industry.

From a practical standpoint, high-fidelity, single-shot readouts pave the way for developing silicon-based quantum computers that can operate alongside classical electronics, enhancing hybrid computing systems. The ultimate goal would be to realize multi-qubit operations and to develop error correction schemes necessitated by quantum error correction protocols.

Looking forward, the research opens avenues for further exploration of silicon-based qubits' coherence properties, the coupling of donor electron spins with nuclear spins for enhanced memory retention, and potential integration into large-scale quantum computing systems. Moreover, combining this method with coherent control techniques to manipulate donor electron and nuclear spins would significantly bolster the capabilities of quantum information science and technology.

In conclusion, this paper not only confirms silicon as a viable material for qubit realization but also enhances the landscape of spintronic devices, offering promising steps towards efficient quantum information processing.