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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Diamond chip under single-photon driving as a high spatial resolution quantum magnetometer and electrometer

Alexander V. Tsukanov, I. Yu. Kateev

Published Dec 30, 2016• 0 citations
Publisher

Abstract

The problem of practical realization of a compact sensing device with high-spatial resolution is addressed. The principle of external field measuring uses analysis of transmission or reflection spectra from a diamond microstructure composed of three-microring optical resonators. Due to Zeeman and Stark shifts of energy levels of NV-centers formed in the microring edge the hybrid electron-photon spectrum changes depending on the strength and direction of magnetic and electric fields, respectively. A probe laser with a tunable wavelength excites the structure in a single-photon regime and its response enables one to detect the fields via spectral behavior. The model of the sensor dynamics accounts for both coherent driving and incoherent processes (center relaxation, dephasing and photon leakage) in terms of Lindblad formalism. With use of the finite-difference time-domain numerical method a three-ring spectrum is calculated and eigenmodes close to NV-center zero-phonon line are found. Electromagnetic field shows whispering-gallery behavior, so NV-center is coupled to a common three-ring mode antinode. As we show in the steady-state regime our approach gives the possibility of external fields measuring in a large intensity range with high sensitivity.

DOI
10.1117/12.2266858

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The problem of practical realization of a compact sensing device with high-spatial resolution is addressed. The principle of external field measuring uses analysis of transmission or reflection spectra from a diamond microstructure composed of three-microring optical resonators. Due to Zeeman and Stark shifts of energy levels of NV-centers formed in the microring edge the hybrid electron-photon spectrum changes depending on the strength and direction of magnetic and electric fields, respectively. A probe laser with a tunable wavelength excites the structure in a single-photon regime and its response enables one to detect the fields via spectral behavior. The model of the sensor dynamics accounts for both coherent driving and incoherent processes (center relaxation, dephasing and photon leakage) in terms of Lindblad formalism. With use of the finite-difference time-domain numerical method a three-ring spectrum is calculated and eigenmodes close to NV-center zero-phonon line are found. Electromagnetic field shows whispering-gallery behavior, so NV-center is coupled to a common three-ring mode antinode. As we show in the steady-state regime our approach gives the possibility of external fields measuring in a large intensity range with high sensitivity.
Quantum sensors based on the nitrogen-vacancy (NV) center in diamond are leading platforms for high-sensitivity magnetometry with nanometer-scale resolution. State-of-the-art implementations, however, typically rely on bulky free-space optics or sacrifice spatial resolution to achieve high sensitivities. Here, we realize an integrated platform that overcomes this trade-off by fabricating monolithic whispering-gallery-mode cavities from a diamond chip containing a high density of NV centers and by evanescently coupling excitation to and photoluminescence from the cavity using a tapered optical fiber. Employing a lock-in-amplified Ramsey magnetometry scheme, we achieve a photon-shot-noise-limited DC sensitivity of 58 nT/Hz58\,\text{nT}/\sqrt{\text{Hz}}58nT/Hz​---the best sensitivity reported to date for a nanofabricated cavity-based magnetometer. The microscopic cavity size enables micrometer-scale spatial resolution and low-power operation, while fiber-coupling provides a path to scalable on-chip integration. Arrays of such sensors could enable NV-NMR spectroscopy of sub-nanoliter samples, new magnetic-gradient imaging architectures, and compact biosensing platforms.
This thesis investigates the theoretical foundations, material properties, and experimental realization of quantum sensors based on the Nitrogen-Vacancy (NV) centers in diamond, a solid-state system that combines quantum coherence with room-temperature operability. The first chapter introduces the principles of quantum sensing, outlining the fundamental definitions, operating protocols, and physical processes underlying the quantum measurement paradigm. Emphasis is placed on the quantum sensing Hamiltonian and the distinction between various classes of quantum sensors. The second chapter focuses on diamond as a host material and on the NV center as a quantum defect. The electronic structure, optical transitions, and spin properties of the NV center are analyzed in detail. Several techniques of NV-based magnetometry are presented, including continuouswave and pulsed optically detected magnetic resonance (ODMR). The discussion also addresses coherence times (T1, T2, and T∗2 ) and methods of diamond synthesis together with NV-center generation through irradiation and annealing. Chapter three develops the physical theory describing the NV center. The Hamiltonian formalism includes spin-spin, hyperfine, and quadrupolar interactions, as well as couplings to external magnetic fields. The chapter further introduces the Bloch sphere representation, magnetic resonance phenomena, and models of lightmatter interaction, ranging from the semiclassical to the fully quantum Rabi framework. A seven-level rate-equation model is proposed to capture the spin dynamics and optical cycling processes of the NV center. The fourth chapter reports the experimental results. After describing materials and methods, several ODMR-based vector magnetometry experiments are presented, highlighting different spectral regimes and the dependence of resonance features on the external magnetic field geometry. Additional studies demonstrate temperature sensing and microwave-free magnetometry techniques for mapping magnetic field distributions. Sensitivity analysis and calibration procedures are also discussed.
Precision measurements of electric current flow in motors and power converters is indispensable for efficient digital control by monitoring their energy use. Nitrogen-vacancy (NV) centers in a crystalline diamond are promising candidates for sensitive magnetometry and electric current measurements. In a diamond quantum sensor with NV centers, the Zeeman splitting of the electron spin state of the NV center can be utilized to detect magnetic field. This is because the splitting of the spectral line is proportional to the external magnetic field strength, and the arbitrary constant of the gyromagnetic ratio is independent of both frequency and magnetic field. Then, the Zeeman splitting can be measured with optically detected magnetic resonance (ODMR) spectroscopy.
As one of the most promising candidates of solid-state qubits, nitrogen-vacancy (NV) centers in diamonds have been paid much attention for experimental quantum information processings, such as their energy level structures characterized by microwave absorption probes. In this paper we develop a simplified steady-state spectral method to exactly solve the driven three-level atomic system for fitting the measured microwave absorptions of the NV centers in diamonds. Due to the energy level structures of the NV centers in diamonds which are controllable by applying external magnetic fields, the precision measurements of the ESR spectra of the NV centers in diamond can be used to precisely detect the applied magnetic fields with nanometer spatial scale resolutions. Our steady-state spectral simulations show that the Bz-component (parallel with the axis of the NV centers) of the applied magnetic fields causes the symmetric Zeeman shifts in the zero-field splitting levels, while the B⊥-component (perpendicular to the NV axis mainly) causes the asymmetric Zeeman shifts. Therefore, by exactly probing the steady-state Zeeman shift absorption spectra of the NV centers in diamonds the applied magnetic fields can be detected precisely, at least theoretically.
Abstract Nitrogen-vacancy centers have demonstrated significant potential as quantum magnetometers for nanoscale phenomena and sensitive field detection, attributed to their exceptional spin coherence at room temperature. However, it is challenging to achieve solid-state magnetometers that can simultaneously possess high spatial resolution and high field sensitivity. Here we demonstrate nanoscale quantum sensing with high field sensitivity by using on-chip diamond micro-ring resonators. The ring resonator enables the efficient use of photons by confining them in a nanoscale region, enabling the magnetic sensitivity of 1.0 μT/√Hz on a photonic chip with a measurement contrast of theoretical limit. We also show that the proposed on-chip approach can improve the sensitivity via efficient light extraction with photonic waveguide coupling. Our work provides a pathway toward the development of chip-scale packaged sensing devices that can detect various nanoscale physical quantities for fundamental science, chemistry, and medical applications.
The optical properties of a photonic molecule consisting of three diamond microring cavities are theoretically investigated. The probability of single-photon excitation (optical response) of a photonic molecule by a weak laser field in the steady-state mode with regard to the dissipative effects is calculated using the model analogous to the tight binding approximation. It is shown that the spectrum can be fine tuned by depositing additional layers onto the photonic-molecule surface. The dependences of the wavelength of the mode corresponding to the zero-phonon optical transition in the NV center on the thickness of these layers and refractive index of their material are established. The NV center localized in the electromagnetic field antinode effectively interacts with the photonic molecule eigenmode, which can be observed as anticrossing points in the dependences of the optical response of the system on exciting laser and transition frequencies.