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arXiv:2406.15324 · New Journal of Physics

Spin Squeezing Enhanced Quantum Magnetometry with Nitrogen-Vacancy Center Qutrits

Lea Gassab, Özgür Esat Müstecaplıoğlu

Published Aug 6, 2025• 4 citations
arXivHTMLPDF

Abstract

Abstract We explore the utility of quantum spin squeezing in quantum magnetometry, focusing on three-level (qutrit) Nitrogen-Vacancy (NV) centers within diamond, utilizing a standard Ramsey interferometry pulse protocol. Our investigation incorporates the effects of dephasing and relaxation on NV centers' dynamics during Ramsey measurements, modeled via the Lindblad quantum master equation. We conduct a comparative analysis between the metrological capabilities of a single NV center and a pair of NV centers, considering Quantum Fisher Information both with and without spin squeezing. The quantum correlations between NV centers are assessed through the evaluation of the Kitagawa-Ueda spin squeezing parameter within a two-level manifold. Additionally, parallel calculations are conducted using a two-level model (qubit) for NV centers. Our findings reveal that leveraging qutrits and spin squeezing yields enhanced magnetometric precision, albeit constrained by dephasing effects. Nevertheless, even in the absence of dynamical decoupling methods to mitigate environmental dissipation, strategic timing of squeezing and free evolution can sustain the advantages of qutrit-based magnetometry.

DOI
10.1088/1367-2630/adf87b

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Abstract We explore the utility of quantum spin squeezing in quantum magnetometry, focusing on three-level (qutrit) Nitrogen-Vacancy (NV) centers within diamond, utilizing a standard Ramsey interferometry pulse protocol. Our investigation incorporates the effects of dephasing and relaxation on NV centers' dynamics during Ramsey measurements, modeled via the Lindblad quantum master equation. We conduct a comparative analysis between the metrological capabilities of a single NV center and a pair of NV centers, considering Quantum Fisher Information both with and without spin squeezing. The quantum correlations between NV centers are assessed through the evaluation of the Kitagawa-Ueda spin squeezing parameter within a two-level manifold. Additionally, parallel calculations are conducted using a two-level model (qubit) for NV centers. Our findings reveal that leveraging qutrits and spin squeezing yields enhanced magnetometric precision, albeit constrained by dephasing effects. Nevertheless, even in the absence of dynamical decoupling methods to mitigate environmental dissipation, strategic timing of squeezing and free evolution can sustain the advantages of qutrit-based magnetometry.
Solid-state spin defects, particularly the nitrogen-vacancy (NV) center in diamond, have emerged as powerful platforms for exploring quantum many-body physics and quantum metrology. Their exceptional coherence properties and strong dipolar interactions offer unique opportunities to simulate complex quantum dynamics and engineer entangled states for enhanced sensing beyond the standard quantum limit. However, achieving scalable entanglement in these systems is notoriously difficult due to intrinsic disorder and the complex nature of long-range dipole-dipole interactions. This thesis presents both theoretical and experimental advancements in harnessing quantum dynamics in interacting spin ensembles for quantum-enhanced metrology. A central result is the experimental realization of spin squeezing in a dense ensemble of NV centers, demonstrating a clear path toward overcoming classical limits in solid-state platforms. To further formalize and scale these phenomena, this work develops theoretical frameworks for generating robust spin squeezing under realistic experimental conditions. We show that finite-temperature easy-plane magnetism can be actively leveraged to create scalable squeezed states for the dipolar spin systems on regular lattices. Building upon this, we further extend the result to spatially disordered quantum dipoles. We demonstrate that strongly coupled spin pairs suppress squeezing through dynamical heating, and we propose a selective shelving protocol to mitigate this problem. Furthermore, we also propose a universal protocol for quantum-enhanced sensing that exploits information scrambling, utilizing the natural, scrambling dynamics of strongly interacting many-body systems to effectively amplify weak external signals. Together, the findings detailed in this thesis establish a foundational paradigm for controlling and utilizing solid-state spin ensembles, paving the way for entanglement-enhanced quantum sensors.
Abstract Nitrogen-vacancy (NV) centers in diamond are a leading solid-state platform for quantum technologies. While often operated as qubits, their native ground state is a spin-1 triplet, making them natural qutrits. Here, we develop a quantitative framework to assess the performance of two coupled NV qutrits as a quantum resource in the presence of environmental noise. We model the system with a Hamiltonian including zero-field splitting, Zeeman, and dipole-dipole terms, and study its evolution under a phase-covariant dephasing channel characteristic of solid-state environments. For an Ohmic bath at zero temperature, we derive an exact analytical form for the decay of two-qutrit coherences. Applying this model to maximally entangled and isotropic states, we obtain closed-form expressions for teleportation fidelity and the visibility thresholds required to demonstrate Bell nonlocality and quantum steering. Our central result is a set of analytic formulas for the quantum advantage time, the duration for which these quantum tasks outperform their classical limits, as a function of the bath’s cutoff frequency. This framework provides direct, parameter-level guidance for designing and benchmarking experiments with coupled NV-center qutrits.
So far most well-established quantum sensing techniques based on the negatively charged nitrogen-vacancy (NV) center in diamond utilize the recorded fluorescence intensity to detect the electronic spin states. However, the fluorescence intensity of a NV center is not only dependent on its spin state, but also affected by measurement issues, such as fluctuations of the excitation laser power and charge state transformation of the NV center. Instabilities in terms of output power or polarization changes in the laser source as well as sample drifts during a measurement are common factors that weaken the precision. Here, we demonstrate proof-of-principle of a sensing method making use of the excited-state lifetimes of a NV center for magnetometry experiments.
The Nitrogen-Vacancy (NV) center is becoming a promising qubit for quantum information processing. The defect has a long coherence time at room temperature and it allows spin state initialized and read out by laser and manipulated by microwave pulses. It has been utilized as a ultra sensitive probe for magnetic fields and remote spins as well. Here, we review the recent progresses in experimental demonstrations based on NV centers. We first introduce our work on implementation of the Deutsch-Jozsa algorithm with a single electronic spin in diamond. Then the quantum nature of the bath around the center spin is revealed and continuous wave dynamical decoupling has been demonstrated. By applying dynamical decoupling, a multi-pass quantum metrology protocol is realized to enhance phase estimation. In the final, we demonstrated NV center can be regarded as a ultra-sensitive sensor spin to implement nuclear magnetic resonance (NMR) imaging at nanoscale.
Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( T2∗{T}_{2}^{* }T2∗​ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.
The nitrogen vacancy (NV) center in diamond is a versatile color center used for magnetometry, quantum computing, and quantum communications. In this article, using a single laser beam as a pump and probe, we measure the spin states of the NV center using the Faraday effect and use such measurements to develop a novel magnetic field sensor. Using the spin-state-dependent effect on the left and right circularly polarized light, we probe and confirm the existence of spin-orbit coupling in the NV center at room temperature. The sensitivity of our magnetometer is 350 350~350 nT/Hz\sqrt{Hz}Hz​, limited by the background produced by the laser trapped inside the diamond. We argue that by using an optical cavity and a high-purity diamond, sensitivities in the femtotesla level can be achieved.