This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers in China have extended the lifetime of entanglement in a room-temperature, solid-state system by up to a factor of 240. Led by Shuo Ren and Rui-Jian Liang at the University of Science and Technology of China in Hefei, the team transferred entangled states from the electron spins of solid-state defects to the spins of surrounding atomic nuclei, which are far more resilient to noise.
The research has been published in Physical Review Letters. When two or more quantum particles are entangled, their properties remain correlated no matter how far apart they are: Measuring one immediately tells you something about its entangled partners. This phenomenon is increasingly being explored for quantum sensing and information processing, where entangled networks of quantum bits, or "qubits," can perform tasks beyond the limits of classical systems.
The enduring challenge is that quantum information is quickly destroyed as qubits interact with thermal fluctuations in their surroundings. This noise can be minimized by cooling systems to ultracold temperatures—but today, physicists are also exploring more practical approaches, in which qubits have built-in resilience against their environment while still allowing information to be easily written and read out. One type of qubit now widely studied for this purpose is the "spin defect." These are atomic-scale imperfections in the orderly lattices of solid-state materials, whose electrons can store quantum information in their spin states.
One example is the "color center" in silicon carbide, whose electrons can absorb and re-emit light at characteristic wavelengths. When fabricated just a few nanometers beneath the material's surface, these defects become highly sensitive to external signals, while their spin states can still be set, controlled and read out using light and microwaves. "These color centers are highly attractive for quantum sensing because bringing the spin close to the surface strengthens its interaction with external signals," explains co-author Jin-Shi Xu.
"The drawback is that the electron spin is also more exposed to surface noise, so its coherence and entanglement can decay much faster." To address this challenge, Ren and Liang's team considered how the electrons of color centers interact with the silicon nuclei immediately surrounding them. Most silicon nuclei have no spin, but around 5% are the isotope silicon-29, whose nuclear spin couples to the electron through the hyperfine interaction, allowing the two to become entangled. Silicon-29 spins are difficult to address directly, but they are far more resilient against surface noise than the electrons.
To exploit this advantage, the researchers developed a "SWAP-gate" protocol: a sequence of control pulses that exchanges the quantum states of two qubits. Once an entangled state had been prepared between a color center's electron and a nearby nucleus, the protocol transferred the entanglement to two silicon-29 nuclei, where it was stored before being mapped back to the electron for readout. "This allowed us to use the electron for fast control while using the nuclear spins as the memory," Xu explains.
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