Quantum entanglement is a resource for computation, secure communication, and ultra-precise measurements. In solids, it is typically achieved in diamond or silicon carbide, but two-dimensional materials offer unprecedented spatial resolution for quantum sensors: a scanning probe on a single defect in an hBN layer achieved 1 nanometer, an order of magnitude better than diamond counterparts. Alongside this work, the archive hosts studies of quantum entanglement as geometry, heat capacity as a detector of entanglement over time, and entangled photons in optical fibers, all moving toward practical platforms for quantum technologies. However, entangling spins in hBN itself had not been achieved until now: the dense nuclear environment destroyed electron spin coherence within hundreds of nanoseconds.
The spin defect was created by implanting carbon-13 ions into an hBN crystal followed by high-temperature annealing. A confocal photoluminescence map revealed a single emitter, and photon correlation measurement confirmed its single-photon nature (g(2)(0)=0.21). The defect turned out to be a pair of electron spins separated by several nanometers; one of them is strongly coupled to a carbon-13 nuclear spin, allowing a four-level two-qubit subsystem to be isolated. The electron spin was manipulated with microwave pulses at frequencies separated by 290 MHz, and the nuclear spin with radiofrequency pulses at 141 and 145 MHz in a magnetic field of 73.5 mT. To extend coherence, a Carr-Purcell-Meiboom-Gill (CPMG) sequence with up to 1024 refocusing π-pulses was applied. Entangled states were prepared using nonlocal gates, and the density matrix was reconstructed via quantum state tomography.
The electron spin coherence increased from 141 ns (Hahn echo) to 38±10 μs with 1024 refocusing pulses, a record for hBN at room temperature. The coherence time as a function of pulse number follows a power law with exponent 0.77±0.09, indicating the dominance of slowly fluctuating noise. Four maximally entangled Bell states were prepared with fidelity up to 0.89 (for the Ψ+ state). The nuclear spin was used as a quantum memory in correlation spectroscopy of an alternating magnetic field: the signal persisted up to 1 ms, far beyond the electron spin relaxation time (about 130 μs). Fourier analysis of the extended signal yielded a spectral resolution of 0.7±0.2 kHz, seven times better than without the memory.
This work demonstrates for the first time entanglement of spin qubits in a two-dimensional material at room temperature, placing hBN alongside diamond and silicon carbide as a platform for quantum technologies. Unlike neighboring studies on geometric interpretations of entanglement or heat capacity as its detector, here entanglement is both achieved and used practically: the nuclear spin serves as a long-lived memory, and the electron spin as a fast optical interface. This is the first case where a nuclear-spin quantum memory in hBN enhanced the sensitivity of an alternating magnetic field sensor, confirming the suitability of two-dimensional materials for hybrid quantum devices.
A natural next step is scaling to multiple nuclear spins to create a quantum register and realize multi-spin entanglement. Increasing the number of refocusing pulses and optimizing the isotopic composition of hBN could further extend coherence. Integrating such defects into van der Waals heterostructures would enable quantum sensors with atomic resolution for studying two-dimensional magnetism, moiré potentials, and many-body entanglement in new materials.
The result will impact quantum sensing, solid-state quantum computing, and quantum networks, where spin nodes compatible with photons are needed. Two-dimensional hBN-based sensors could find applications in materials science for mapping magnetic fields with nanometer resolution.
Test entanglement between multiple nuclear spins of a single defect and measure the lifetime of entangled states. Investigate defects with stronger hyperfine coupling to speed up gates and improve fidelity.
For quantum sensing, the question of sensitivity limits at room temperature remains open: nuclear environment noise limits coherence, and this work shows that dynamic decoupling and quantum memory mitigate but do not eliminate the problem. Also unresolved is the challenge of scaling entanglement to dozens of qubits in solids without loss of fidelity.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This work demonstrates quantum entanglement between electron and nuclear spins in hBN at room temperature. Using carbon-13 implantation, the authors created a two-qubit system, extended the electron spin coherence to 38 μs with CPMG, prepared Bell states with a fidelity of 0.89, and used the nuclear spin as a memory for correlation spectroscopy with a resolution of 0.7 kHz.
Where its strength is
The record coherence in hBN at room temperature and the demonstration of entanglement with a nuclear memory open the path to scalable quantum sensors based on two-dimensional materials.
Where it could go next
Worth trying
Why this may matter
This result brings quantum sensors closer to practical applications in biology and materials science, thanks to the atomic thickness of hBN and its operation at room temperature.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.56, against a usual 0.64. It looks like few have drilled nearby.
The electron spin coherence time after dynamic decoupling (38 μs) is 270 times longer than the original (141 ns). If a car increased its range by the same factor, it would go from 5 km to 1350 km.
The idea of a nuclear-spin quantum memory echoes the concept of an 'ancilla' from science fiction, a auxiliary quantum object that stores information while the main qubit interacts with the environment. In Greg Egan's novel 'Quarantine', quantum states are used as a computational resource, and here the nuclear spin plays the role of such a 'buffer' for the electron sensor.