Scientists have achieved quantum entanglement of up to 27 nuclear spins of phosphorus atoms in a silicon crystal. This milestone represents the largest number of entangled nuclear spin qubits to date in a solid-state material, surpassing previous limits and demonstrating the feasibility of using these systems for quantum computing. The experiment was conducted at cryogenic temperatures and under a magnetic field, using microwave and radiofrequency pulses to manipulate the nuclear and electronic spins.

Multiparticle entanglement is a fundamental resource for quantum computing, quantum simulation, and precision metrology. Nuclear spins are attractive as qubits due to their long coherence times, which can extend for hours or even days. However, their weak coupling to the environment and to each other, which grants them this coherence, also makes their manipulation and entanglement challenging. This work directly addresses this challenge by demonstrating precise control over a system of multiple nuclear spins in a solid-state environment.

To achieve entanglement, the team used an electronic spin qubit of a phosphorus atom as an intermediary to mediate the interaction between the nuclear spins. Through carefully calibrated pulse sequences, they were able to generate entangled states of up to 27 nuclear spins, verifying the entanglement through tomographic reconstruction of the quantum states. The fidelity of the generated entangled states remained high, which is crucial for practical applications.

This breakthrough opens new avenues for the development of scalable quantum processors based on nuclear spins in silicon, a well-established material in the semiconductor industry. The ability to entangle such a large number of qubits with high fidelity is a crucial step towards building fault-tolerant quantum computers and exploring complex quantum phenomena in many-body systems. Future steps will include increasing the number of entangled qubits and implementing more sophisticated quantum algorithms.