Cavity-enhanced magnetic-field sensing via stimulated emission from nitrogen-vacancy centres in diamond

Media type: E-Book

Title: Cavity-enhanced magnetic-field sensing via stimulated emission from nitrogen-vacancy centres in diamond

Contributor: Hahl, Felix Anton [Verfasser]; Jeske, Jan [Akademischer Betreuer]; Ambacher, Oliver [Sonstige]; Elsässer, Christian [Sonstige]

Corporation: Fraunhofer-Institut für Angewandte Festkörperphysik ; Albert-Ludwigs-Universität Freiburg, Fakultät für Angewandte Wissenschaften

imprint: Freiburg: Universität, 2022

Extent: Online-Ressource

Language: English

DOI: 10.6094/UNIFR/232328

Identifier:

Keywords: Diamant ; Quantum technology ; Quantum sensing ; Nitrogen-vacancy (NV) centre ; Laser threshold magnetometry ; NV laser ; Diamond ; Magnetic-field quantum sensor ; (local)doctoralThesis

Origination:

University thesis: Dissertation, Universität Freiburg, 2022

Footnote:

Description: Abstract: Magnetic-field quantum sensors are among the most advanced technologies of the rapidly developing quantum technologies in terms of a commercial application. The most sensitive magnetometers are SQUIDs (superconducting quantum interference devices) and OPMs (optically pumped magnetometers), based on atomic vapour cells. Both technologies reach sensitivities to magnetic fields below 1 fT / √ Hz and beat classical hall probe sensors by more than six orders of magnitude. SQUIDS are established in medical diagnostics of neuronal activity. However, the SQUID technology is based on superconductivity and requires cryogenic cooling. OPMs are atomic vapour cells, thus they need to be heated and require shielding against external magnetic fields, as they can only be operated in a zero-field environment. As a consequence, high technical effort and high fiancial costs are associated with the implementation of these technologies. The negatively charged nitrogen-vacancy (NV) centre in diamond is a promising magnetic-field quantum sensor. The unique properties of this point defect in dia- mond have caused great attention. The single-electron-spin system is energetically located in the band gap of diamond, and thus forms an optically accessible quantum bit. It can be operated in ambient conditions and in background magnetic fields and serves as a robust sensor due to the extraordinary properties of diamond in terms of hardness, optical transparency and thermal conductivity. Current NV ensemble magnetometers reach sensitivities of 1 pT/ √ Hz limited by photoluminescence (PL) collection efficiency, reduced spin-coherence time and a low contrast of 1% − 5 % in highly NV-doped diamond. Laser threshold magnetometry (LTM) has been a theoretical approach for the improvement of the NV centre ensemble sensitivity to 1 fT/ √ Hz. This would enable to close the gap in sensitivity reached by SQUIDs and OPMs, but with a diamond-based, robust room-temperature sensor. The high sensitivity via LTM is reached by an increased signal strength and magnetic-field contrast due to the non-linear enhancement caused by stimulated emission in an NV lasing cavity. Many theoretical and experimental attempts have been made to realise LTM. Weak stimulated emission has been evidenced in a single transmission experiment of the diamond via lock-in detection and amplification in a fibre cavity has been detected with single-photon detectors. A magnetic-field dependency of the stimulated emission has not been detected, so far. In this work, the principle of laser threshold magnetometry is experimentally demonstrated for the first time. The experiments are based on a macroscopic high-finesse laser cavity of 1.4 cm cavity length. In the laser cavity, the NV centres are pumped with a laser at 532 nm and the cavity is resonantly seeded with a laser at 710 nm. A novel, reproducible process was invented which produces a highly NV-doped and ultra-low absorbing diamond gain material. In this process, the diamond is low- pressure, high-temperature (LPHT) pre-treated at 1800 °C in vacuum or hydrogen atmosphere before the NV creation process of electron irradiation and subsequent annealing at 1000 °C. This significantly reduces the absorption of highly NV-doped diamond by 124% − 1544% compared to reference samples, which were only treated with the generally established NV creation process. At the same time the new process keeps a high NV concentration and increases the PL emission by 60%. By optically pumping the NV centres in the cavity an amplification by stimulated emission is detected which reaches a maximum of 64% between 1 W − 2 W of pumping power. The emission shows a maximal output power in the mW regime. The measurements reveal a previously unknown effect of induced absorption as an additional loss channel in the diamond medium which reduces the amplification and the cavity finesse at pump intensities ≥ 10 kW/cm. This induced absorption prevents the NV centres from self-sustained lasing activity. A permanent magnetic field with a major transverse component Bx, i.e. perpendicular to the NV direction, is applied to the NV centres. The contrast between the cavity signal of applied magnetic field and non-magnetic field reaches 33 % and exceeds the maximum theoretically achievable contrast of the generally established detection via the PL of the NV centres. Thus, in this work magnetic-field-dependent stimulated emission from NV centres is demonstrated for the first time. Furthermore, the first optically detected magnetic resonance (ODMR) via stimulated emission with a contrast between resonant and off -resonant microwave field of 17 % is demonstrated in this work. This contrast is higher than the simultaneously detected ODMR contrast of the PL that reaches 11 %. With the novel magnetic-field sensor based on stimulated emission, a shot-noise limited DC sensitivity of (29.1 ± 2.5) pT/ √ Hz having a coherent laser signal output in the mW range is achieved. This is an improvement of almost one order of magnitude compared to the simultaneously detected PL sensitivity. The advances presented in this work in sensing magnetic fields via stimulated emission of NV centres will have a significant contribution to quantum sensing and enable the exploration of coherent readout of quantum systems

Access State: Open Access

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