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arXiv:2510.19598

Zero-field identification and control of hydrogen-related electron-nuclear spin registers in diamond

Alexander Ungar, Hao Tang, Andrew Stasiuk, Bo Xing, Boning Li, Ju Li, Alexandre Cooper, Paola Cappellaro

quant-phSubmitted Oct 22, 2025• Announced Oct 23, 2025
v1 · Oct 22, 2025v2 · Jan 29, 2026v3 · Apr 8, 2026v4 · Oct 30, 2026
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Abstract

Spin defects in diamond serve as powerful building blocks for quantum technologies, especially for applications in quantum sensing and quantum networks. Electron-nuclear defects formed in the environment of optically active spins, such as the nitrogen-vacancy (NV) center, can be harnessed as qubits to construct larger hybrid quantum registers. However, many of these defects have yet to be characterized, limiting their integration into scalable devices. Here, we introduce an approach to identify the hyperfine components and nuclear spin species of spin defects through measurements on a nearby NV center. This approach combines double electron-electron resonance performed at zero field (ZF-DEER) with nuclear-electron-electron triple resonance (NEETR), which we use to characterize two unknown defects at the single-spin level, yielding self-consistent results. These results provide a guide to resolving the defect structures using $\textit{ab initio}$ calculations, leading to the identification of a new hydrogen defect structure and an accurate match to a previously identified nitrogen defect. Building on the NEETR protocol, we then demonstrate initialization, unitary control, and long-lived coherence of the nuclear spin qubit of the hydrogen defect with $T_2 = 1.0(3)\,\mathrm{ms}$. Our characterization and control tools establish a framework to expand the accessible defect landscape for hybrid electron-nuclear registers and enable applications in quantum sensing, networks, and atomic-scale magnetic resonance imaging at room temperature.

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Spin defects in diamond serve as powerful building blocks for quantum technologies, especially for applications in quantum sensing and quantum networks. Electron-nuclear defects formed in the environment of optically active spins, such as the nitrogen-vacancy (NV) center, can be harnessed as qubits to construct larger hybrid quantum registers. However, many of these defects have yet to be characterized, limiting their integration into scalable devices. Here, we introduce an approach to identify the hyperfine components and nuclear spin species of spin defects through measurements on a nearby NV center. This approach combines double electron-electron resonance performed at zero field (ZF-DEER) with nuclear-electron-electron triple resonance (NEETR), which we use to characterize two unknown defects at the single-spin level, yielding self-consistent results. These results provide a guide to resolving the defect structures using ab initio\textit{ab initio}ab initio calculations, leading to the identification of a new hydrogen defect structure and an accurate match to a previously identified nitrogen defect. Building on the NEETR protocol, we then demonstrate initialization, unitary control, and long-lived coherence of the nuclear spin qubit of the hydrogen defect with T2=1.0(3) msT_2 = 1.0(3)\,\mathrm{ms}T2​=1.0(3)ms. Our characterization and control tools establish a framework to expand the accessible defect landscape for hybrid electron-nuclear registers and enable applications in quantum sensing, networks, and atomic-scale magnetic resonance imaging at room temperature.
We experimentally demonstrate an approach to scale up quantum devices by harnessing spin defects in the environment of a quantum probe. We follow this approach to identify, locate, and control two electron-nuclear spin defects in the environment of a single nitrogen-vacancy center in diamond. By performing spectroscopy at various orientations of the magnetic field, we extract the unknown parameters of the hyperfine and dipolar interaction tensors, which we use to locate the two spin defects and design control sequences to initialize, manipulate, and readout their quantum state. Finally, we create quantum coherence among the three electron spins, paving the way for the creation of genuine tripartite entanglement. This approach will be useful in assembling multispin quantum registers for applications in quantum sensing and quantum information processing.
A promising approach for multi-qubit quantum registers is to use optically addressable spins to control multiple dark electron-spin defects in the environment. While recent experiments have observed signatures of coherent interactions with such dark spins, it is an open challenge to realize the individual control required for quantum information processing. Here, we demonstrate the heralded initialisation, control and entanglement of individual dark spins associated to multiple P1 centers, which are part of a spin bath surrounding a nitrogen-vacancy center in diamond. We realize projective measurements to prepare the multiple degrees of freedom of P1 centers-their Jahn-Teller axis, nuclear spin and charge state-and exploit these to selectively access multiple P1s in the bath. We develop control and single-shot readout of the nuclear and electron spin, and use this to demonstrate an entangled state of two P1 centers. These results provide a proof-of-principle towards using dark electron-nuclear spin defects as qubits for quantum sensing, computation and networks.
Nitrogen-vacancy centers in diamond are sensitive probes of time-varying magnetic fields that can be used to identify unknown spin defects in their nearby environment. Performing spectral quantum measurements on such single quantum probes enables gaining information about the internal structure and dynamics of nearby spin defects that would otherwise be inaccessible through direct or indirect measurements with classical probes. Here, we identify a system composed of two electron-nuclear spin defects in a diamond crystal by performing a series of spectral identification measurements using a single nitrogen-vacancy center in diamond. Besides enabling the identification of new spin defects and studies of their formation mechanisms, these techniques will be useful for scaling up quantum systems by converting environmental spin defects into quantum resources.
Digital information based on the laws of quantum mechanics promisses powerful new ways of computation and communication. However, quantum information is very fragile; inevitable errors continuously build up and eventually all information is lost. Therefore, realistic large-scale quantum information processing requires the protection of quantum bits (qubits) against errors. In this thesis we present the experimental implementation of quantum error correction protocols based on spins in diamond. In such protocols, a quantum state is protected against errors by encoding in multiple qubits. Errors can be detected and corrected by measurement of correlations, so-called stabilizer-measurements, on these qubits.The experimental work presented in this thesis employs multiple spins in diamond as qubits to explore and implement error correction protocols. The nitrogen-vacancy (NV) centre in diamond is a lattice defect consisting of a nitrogen atom (N) and a vacancy (V) on two adjacent diamond lattice sites. This defect effectively results in an electronic spin that can be addressed as a qubit. The spin state can be manipulated by microwave fields and optically read out. At liquid helium temperatures (cryogenic temperature, ~4 K = -269 C), the NV electron spin provides high-fidelity single-shot readout and long coherence times.The NV centre is surrounded by naturally available (1.1% abundance) nuclear C13 spins. As the number of spins that are close enough to the NV centre to be strongly coupled is limited, we employ the weakly coupled nuclear spins in the spin bath of the NV centre. Using dynamical decoupling techniques these nuclear spins can be detected via the NV electron spin through the hyperfine interaction. The nuclear spins are long-lived and robust against optical excitation of the NV electron spin, which can make these spins a robust quantum register for quantum error correction.In Ch. 4 we demonstrate universal control over multiple of such weakly coupled nuclear C13 spins in the environment of the NV centre at ambient temperatures. We demonstrate initialization, control and read-out of individual nuclear spins. Finally, we implement a quantum error correction protocol by encoding a quantum state in the NV electron spin and two nuclear spins. Errors are detected by un-encoding the quantum state back to the electron spin and correction via a double controlled operation.For universal fault-tolerant quantum computations it is essential that the quantum information remains encoded at all times. In Ch. 5 we present multiple rounds of quantum error correction and active feedback on a continuously encoded qubit at cryogenic temperatures. A quantum state is protected by encoding in three weakly coupled spins. Errors are detected via high-fidelity non-demolition readout of the NV electron spin and actively corrected using fast classical electronics. We demonstrate that an actively error-corrected qubit is robust against phase flip errors and show that a superposition state can live longer than the best physical qubit in the encoding.The presented methods and results can be extended to a range of future experiments. In Ch. 6 we propose the implementation of five-qubit quantum error correction, the smallest code to correct for general single-qubit errors on the physical qubits in the encoding, by extending the experimental methods as developed in Chs. 4&5. Besides the exploration and development of larger error correction protocols and fault-tolerant quantum computing, the presented quantum register based in spins in diamond can be employed as a quantum node and combined with recent advances in the realization of quantum entanglement over large distances to form quantum networks. These networks can be used to study both fundamental questions as well as future applications in quantum information technology.
Electron spin qubits associated with individual solid-state defects can exhibit exceptional coherence and bright optical interfaces. Furthermore, their magnetic interactions with nuclear spins in the host material present a resource for multi-qubit registers. They have thus emerged as powerful systems with which to develop quantum technologies. In this thesis, we develop a toolbox for the precise control of multi-qubit spin systems associated with single nitrogen-vacancy centres in diamond. We utilise this platform to explore a number of avenues in quantum science: networks, computation, sensing, and simulation. Our findings provide new insights towards the goal of distributed quantum computation, and establish a programmable solid-state-spin quantum simulator for studying many-body physics.
A negatively-charged nitrogen-vacancy (NV) center in diamond is a promising system for quantum computation and quantum information. It has the diamond structure with a substitutional nitrogen atom and a neighboring vacancy. An electron spin in the NV center has an exceptionally long coherence time at room temperature. Thus the NV center has a potential to realize a room-temperature quantum computer which is more efficient than a classical computer. In this dissertation, we focus on the nitrogen nuclear spin as well as the electron spin in the NV center. Every NV center has the nitrogen nuclear spin. Because of the long coherence time of the nitrogen nuclear spin, it is a good candidate for a quantum memory. Thus it is important to prepare the nitrogen nuclear spin qubit in a given pure state for quantum computation. We provide a theoretical understanding of the popular nuclear spin initialization technique. Furthermore, we propose an optimal condition for the initialization of the nitrogen nuclear spin by including the local strain in the NV center. We expect that this optimal condition can improve the purity of the nuclear spin initialization. We also propose an efficient quantum measurement protocol for the hyperfine interaction between the electron spin and the ¹⁵N nuclear spin in the NV center. A precise knowledge of the hyperfine interaction is important to reduce an error in a coherent control of the ¹⁵N nuclear spin. In this protocol, a sequence of quantum operations with successively increasing duration is utilized to estimate the hyperfine interaction with successively higher precision approaching the quantum metrology limit. Unlike common quantum metrological methods, this protocol does not need the preparation of the nuclear spin in a pure state. In the presence of realistic operation errors and electron spin decoherence, we show the overall precision of our protocol still surpasses the standard quantum limit