Storing quantum information for 30 seconds in a nanoelectronic device.

Area of Science:

• Quantum information science
• Solid-state physics
• Semiconductor spintronics

Background:

• Semiconductor-based qubits offer a scalable path for quantum information devices.
• Solid-state environments can introduce decoherence through interactions with nuclear spins and charge fluctuations.
• Isotopic enrichment of silicon-28 (28Si) is known to reduce decoherence in bulk spin ensembles.

Purpose of the Study:

• To investigate the coherent operation of single electron and nuclear spin qubits in a gated nanostructure fabricated on an isotopically engineered (28)Si substrate.
• To assess the coherence times and control fidelity of these qubits.
• To identify the dominant sources of decoherence in such devices.

Main Methods:

• Fabrication of a top-gated nanostructure on an isotopically purified (28)Si substrate.
• Coherent manipulation and readout of individual phosphorus-31 ((31)P) electron and nuclear spin qubits.
• Application of Carr-Purcell-Meiboom-Gill (CPMG) sequences to measure coherence times.
• Detailed noise spectroscopy to identify decoherence mechanisms.

Main Results:

• Demonstrated coherent operation of individual (31)P electron and nuclear spin qubits.
• Achieved a benchmark coherence time exceeding 30 seconds for the (31)P nuclear spin qubit using CPMG.
• Reached over 99.99% control fidelity for the (31)P nuclear spin qubit.
• Measured an electron spin CPMG coherence time exceeding 0.5 seconds.
• Noise spectroscopy indicated that decoherence is not limited by proximity to the interface, but likely by external thermal and magnetic noise.

Conclusions:

• Single spin qubits in (28)Si nanostructures exhibit long coherence times, setting a new benchmark for solid-state qubits.
• The results challenge the assumption that interfaces are the primary decoherence source in such devices.
• Decoherence appears to be dominated by external noise, suggesting avenues for further improvement and scalability.