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Journal of Quantum Information Science

Exploring Spin Mixing with Fluorescence Microscopy

Cecelia Embleton, Oscar Chen, Zihan Yu

Published Jan 1, 2025• 0 citations
Publisher

Abstract

Point defects in diamond, also known as color centers, offer unique possibilities for solid-state quantum magnetometry. Here, we demonstrate and explore quantum spin mixing and optical readout of nitrogen vacancy diamond quantum states with a portable, educational toolkit from Quantum Education Initiative. Visible light photons electronically excite NV centers, upon which their integrated photoluminescence is measured through a free-space photodetector. With household magnets, changes in photoluminescence are correlated with changes in the NV electrons magnetic spin state to intuitively understand optical initialization and readout of an NV ensemble. As a continuous wave laser is used for excitation, we do not demonstrate the trivial procedure for optical readout for quantum gates. Rather, we employ a magnet with a non-zero transverse field component to induce steady-state spin mixing, allowing us to observe decreases in photoluminescence due to occupation of the m s =±1 sublevels.

DOI
10.4236/jqis.2025.153008

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Point defects in diamond, also known as color centers, offer unique possibilities for solid-state quantum magnetometry. Here, we demonstrate and explore quantum spin mixing and optical readout of nitrogen vacancy diamond quantum states with a portable, educational toolkit from Quantum Education Initiative. Visible light photons electronically excite NV centers, upon which their integrated photoluminescence is measured through a free-space photodetector. With household magnets, changes in photoluminescence are correlated with changes in the NV electrons magnetic spin state to intuitively understand optical initialization and readout of an NV ensemble. As a continuous wave laser is used for excitation, we do not demonstrate the trivial procedure for optical readout for quantum gates. Rather, we employ a magnet with a non-zero transverse field component to induce steady-state spin mixing, allowing us to observe decreases in photoluminescence due to occupation of the m s =±1 sublevels.
The nitrogen-vacancy center in diamond offers unique possibilities for room-temperature quantum magnetometry. Here, we demonstrate and explore diamond magnetometry with a portable, educational toolkit from Quantum Education Initiative (QEI). A green (532 nm) laser diode and optical elements are used to electronically excite NV− electrons, while a transverse magnetic field induces spin mixing. Through all-optical initialization and readout (fluorescence), we gained a conceptual understanding of diamond-based magnetometry. We aligned several optical elements and measured intensity data to create an intensity versus magnetic field relationship. The employed magnetometry scheme does not attain state of the art sensitivities, but it is purely employed for educational purposes.
Abstract Transverse-magnetic-field-induced spin mixing in nitrogen-vacancy (NV) centers hybridizes the |0⟩ and | ± 1⟩ manifolds, degrading optical spin polarization and spin-dependent fluorescence and thereby limiting optically detected magnetic resonance (ODMR) contrast and quantum-sensor fidelity. While recent work has clarified key elements of NV photophysics, how spin mixing evolves with temperature under device-relevant operating conditions─and how it intertwines with charge-state dynamics─remains insufficiently quantified. Here we perform systematic magnetic-field-temperature (B-T) mapping of transverse-field-induced photoluminescence (PL) quenching in an ensemble of NV centers. By spectrally resolving the NV– and NV0 zero-phonon-line emission, we disentangle spin-mixing-driven contrast loss within NV– from correlated changes in charge-state-resolved fluorescence. We introduce an operational critical field Bc extracted from the PL-contrast line shape, which provides a compact, reproducible figure-of-merit for transverse-field robustness and enables straightforward comparison across temperatures and field geometries. The measured temperature dependence of Bc is captured by a concise model incorporating phonon-mediated excited-state orbital dynamics, establishing a predictive framework for optimizing operating conditions and benchmarking ensemble NV sensing platforms.
The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers (NV), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the NV centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems.
The color centers in diamonds are promising candidates in the context of quantum information science, quantum computation, and spin-based quantum sensors due to their exceptional spin-dependent emission properties. The manipulation and the optical readout of the spin state is measured using a spectroscopic technique known as the Optically Detected Magnetic Resonance (ODMR). Here, we discuss the indigenous development of an ODMR setup to manipulate and measure the spin state of nitrogen-vacancy centers in diamond. The study involves the confocal mapping of NV centers to measure the spin state by applying a micro-wave field. The spin state control appears as a dip in the measured emission intensity as a function of micro-wave frequency.
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.