arXiv subjects

Manuel Rieger

Publications and source records attributed to Manuel Rieger.

5 recordsLinked to original sources

arXiv2025

Mitigating the Transition of SiV$^-$ in Diamond to an Optically Dark State

Negatively charged silicon vacancy centers in diamond (SiV$^-$) are promising for quantum photonic technologies. However, when subject to resonant optical excitation, they can inadvertently transfer into a zero-spin optically dark state. We show that this unwanted change of charge state can be quickly reversed by the resonant laser itself in combination with static electric fields. By defining interdigitated metallic contacts on the diamond surface, we increase the steady-state SiV$^-$ photoluminescence under resonant excitation by a factor $\ge3$ for most emitters, making it practically constant for certain individual emitters. We electrically activate single \sivs near the positively biased electrode, which are entirely dark without applying local electric fields. Using time-resolved 3-color experiments, we show that the resonant laser not only excites the SiV$^-$, but also creates free holes that convert SiV$^{2-}$ to SiV$^-$ on a timescale of milliseconds. Through analysis of several individual emitters, our results show that the degree of electrical charge state controllability differs between individual emitters, indicating that their local environment plays a key role. Our proposed electric-field-based stabilization scheme enhances deterministic charge state control in group-IV color centers and improves its understanding, offering a scalable path toward quantum applications such as entanglement generation and quantum key distribution.

quant-ph↗

arXiv2025

Second-order Stark shifts exceeding 10$\,$GHz in electrically contacted SiV$^-$ centers in diamond

Negatively charged silicon vacancy centers (SiV$^-$) in diamond exhibit excellent spin coherence and optical properties, making them promising candidates for quantum technologies. However, the strain-induced inhomogeneous distribution of optical transition frequencies poses a challenge for scalability. We demonstrate electrical tuning of the SiV$^-$ center zero-phonon lines using in-plane contacts to apply moderate electric fields up to 45$\,$MV/m. The second-order Stark shift exceeds 10$\,$GHz, which is of the same order of magnitude as the 15$\,$GHz inhomogeneous distribution of SiV$^-$ observed in emitters embedded in optical nanostructures such as photonic crystal nanocavities. Analysis of individual SiV$^-$ centers shows significant variation in polarizabilities between defects indicating that the polarizability strongly depends on local parameters like strain. The observed polarizabilities are 3-25 times larger than those of tin vacancy centers, which we attribute to valence band resonances that delocalize the $e_u$ wavefunctions. Photoluminescence excitation measurements reveal that optical linewidths increase moderately with applied electric field strength. Our results demonstrate that large electrical Stark shifts can overcome the inhomogeneous distribution of transition frequencies, representing a significant step toward scalable SiV$^-$-based quantum technologies such as quantum repeaters.

quant-ph↗

arXiv2025

Temperature-Dependent Emission Spectroscopy of Quantum Emitters in Hexagonal Boron Nitride

Color centers in hexagonal boron nitride (hBN) have attracted significant interest due to their potential applications in future optical quantum technologies. For most applications, scalable on-demand fabrication is a key requirement. Recent advances using localized electron irradiation have demonstrated near-identical emitters in the blue and yellow spectral regions. While the blue emitters have been demonstrated in cryogenic temperatures, the yellow emitters remain uncharacterized under such conditions. In this work, we therefore extended the study of yellow emitters to cryogenic temperatures. Initially, multiple spectral features were observed, prompting a systematic investigation that led to the identification of a defect emission centered around 547.5 nm with high brightness and excellent photostability. By tuning the excitation wavelength, we are able to distinguish Raman scattering peaks from the emitter emission. Further analysis of the vibronic emissions allowed us to identify an optical phonon mode, whose contribution becomes increasingly dominant at elevated temperatures. Photoluminescence excitation spectroscopy (PLE) reveals excitation through this phonon mode enhances the emission by almost 5-fold in cryogenic temperature. Temperature-dependent studies further elucidate the role of phonons in the emission process. These observations deepen our understanding of the nature of the emitters, opening new avenues for precise tuning of quantum light sources.

physics.optics↗

arXiv2023

Fast optoelectronic charge state conversion of silicon vacancies in diamond

Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications for photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multi-qubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photo-current spectroscopy. We controllably convert the charge state between the optically active SiV$^-$ and dark SiV$^{2-}$ with MHz rates and 90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV$^-$ photoluminescence under hole-capture, measure the intrinsic conversion time from the dark SiV$^{2-}$ to the bright SiV$^-$ to be 36.4(6.7)ms and demonstrate how it can be enhanced by a factor of $10^5$ via optical pumping. Moreover, we obtain new information on the defects that contribute to photo-conductivity, indicating the presence of substitutional nitrogen and divacancies.

quant-ph↗

arXiv2023

Three-photon excitation of quantum two-level systems

We demonstrate that semiconductor quantum dots can be excited efficiently in a resonant three-photon process, whilst resonant two-photon excitation is highly suppressed. Time-dependent Floquet theory is used to quantify the strength of the multi-photon processes and model the experimental results. The efficiency of these transitions can be drawn directly from parity considerations in the electron and hole wavefunctions in semiconductor quantum dots. Finally, we exploit this technique to probe intrinsic properties of InGaN quantum dots. In contrast to non-resonant excitation, slow relaxation of charge carriers is avoided which allows us to measure directly the radiative lifetime of the lowest energy exciton states. Since the emission energy is detuned far from the resonant driving laser field, polarization filtering is not required and emission with a greater degree of linear polarization is observed compared to non-resonant excitation.

quant-ph↗