arXiv subjects

Ignas Masiulionis

Publications and source records attributed to Ignas Masiulionis.

8 recordsLinked to original sources

arXiv2026

Optical decoherence in Er$^{3+}$-doped CeO$_2$ spin qubit platforms

Erbium ions (Er$^{3+}$) in cerium dioxide (CeO$_2$) represent a promising spin-photon interface for quantum communication, but the mechanisms limiting their optical coherence remain poorly understood. Using periodic hybrid density functional theory calculations with finite-size corrections, we identify Ce$^{3+}$ polarons and their complexes with oxygen vacancies and Er$^{3+}$ dopants as likely sources of optical decoherence. These defects exhibit finite photoionization cross-sections at 0.8 eV, coinciding with both the laser excitation energy used experimentally and the emission energy of Er$^{3+}$. This resonance enables photoionization of the polarons and photoluminescence quenching of Er$^{3+}$, leading to the broadening of optical linewidths, shortening of excited-state lifetimes, and introduction of charge noise. Our concentration-dependent photocurrent measurements in Er$^{3+}$-doped CeO$_2$ films under 0.8 eV illumination validate the predicted decoherence pathway. Our combined computational and experimental results identify a concrete defect-engineering target for improving the Er$^{3+}$-doped CeO$_2$ platform, and point to a decoherence mechanism likely relevant to other Er$^{3+}$-doped multivalent-oxide quantum platforms.

cond-mat.mtrl-sci↗

arXiv2025

Microstructural and preliminary optical and microwave characterization of erbium doped CaMoO$_4$ thin films

This work explores erbium-doped calcium molybdate (CaMoO$_4$) thin films grown on silicon and yttria stabilized zirconia (YSZ) substrates, as a potential solid state system for C-band (utilizing the $\sim$1.5 $μ$m Er$^{3+}$ 4f-4f transition) quantum emitters for quantum network applications. Through molecular beam epitaxial growth experiments and electron microscopy, X-ray diffraction and reflection electron diffraction studies, we identify an incorporation limited deposition regime that enables a 1:1 Ca:Mo ratio in the growing film leading to single phase CaMoO$_4$ formation that can be in-situ doped with Er (typically 2-100 ppm). We further show that growth on silicon substrates is single phase but polycrystalline in morphology; while growth on YSZ substrates leads to high-quality epitaxial single crystalline CaMoO$_4$ films. We perform preliminary optical and microwave characterization on the suspected $Y_1 - Z_1$ transition of 2 ppm, 200 nm epitaxial CaMoO$_4$ annealed thin films and extract an optical inhomogeneous linewidth of 9.1(1) GHz, an optical excited state lifetime of 6.7(2) ms, a spectral diffusion-limited homogeneous linewidth of 6.7(4) MHz, and an EPR linewidth of 1.10(2) GHz.

cond-mat.mtrl-sci↗

arXiv2025

Spin decoherence dynamics of Er$^{3+}$ in CeO$_2$ film

Developing telecom-compatible spin-photon interfaces is essential towards scalable quantum networks. Erbium ions (Er$^{3+}$) exhibit a unique combination of a telecom (1.5 $μ$m) optical transition and an effective spin-$1/2$ ground state, but identifying a host that enables heterogeneous device integration while preserving long optical and spin coherence remains an open challenge. We explore a new platform of Er$^{3+}$:CeO$_2$ films on silicon, offering low nuclear spin density and the potential for on-chip integration. We demonstrate a 38.8 $μ$s spin coherence, which can be extended to 176.4\nobreakspace $μ$s with dynamical decoupling. Pairing experiments with cluster correlation expansion calculations, we identify spectral diffusion-induced Er$^{3+}$ spin flips as the dominant decoherence mechanism and provide pathways to millisecond-scale coherence.

quant-ph↗

arXiv2024

Isolation of individual Er quantum emitters in anatase TiO$_2$ on Si photonics

Defects and dopant atoms in solid state materials are a promising platform for realizing single photon sources and quantum memories, which are the basic building blocks of quantum repeaters needed for long distance quantum networks. In particular, trivalent erbium (Er$^{3+}$) is of interest because it couples C-band telecom optical transitions with a spin-based memory platform. In order to produce quantum repeaters at the scale required for a quantum internet, it is imperative to integrate these necessary building blocks with mature and scalable semiconductor processes. In this work, we demonstrate the optical isolation of single Er$^{3+}$ ions in CMOS-compatible titanium dioxide (TiO$_2$) thin films monolithically integrated on a silicon-on-insulator (SOI) photonics platform. Our results demonstrate a first step toward the realization of a monolithically integrated and scalable quantum photonics package based on Er$^{3+}$ doped thin films.

quant-ph↗

arXiv2024

Anomalous Purcell decay of strongly driven inhomogeneous emitters coupled to a cavity

We perform resonant fluorescence lifetime measurements on a nanocavity-coupled erbium ensemble as a function of cavity-laser detuning and pump power. Our measurements reveal an anomalous three-fold suppression of the ensemble Purcell factor at zero cavity detuning and high pump fluence. We capture qualitative aspects of this decay rate suppression using a Tavis-Cummings model of non-interacting spins coupled to a common cavity.

quant-ph↗

arXiv2023

Optical and microstructural characterization of Er$^{3+}$ doped epitaxial cerium oxide on silicon

Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies such as quantum memory, due to the intrinsic spin-photon interface of the rare-earth ion combined with the integration methods available in the solid-state. Erbium-doped cerium oxide (Er:CeO$_2$) is a particularly promising platform for such a quantum memory, as it combines the telecom-wavelength (~1.5 $μ$m) 4f-4f transition of erbium, a predicted long electron spin coherence time supported by CeO$_2$, and is also near lattice-matched to silicon for heteroepitaxial growth. In this work, we report on the epitaxial growth of Er:CeO$_2$ thin films on silicon using molecular beam epitaxy (MBE), with controlled erbium concentration down to 2 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO$_2$ host structure, and characterize the spin and optical properties of the embedded Er$^{3+}$ ions. In the 2-3 ppm Er regime, we identify EPR linewidths of 245(1) MHz, optical inhomogeneous linewidths of 9.5(2) GHz, optical excited state lifetimes of 3.5(1) ms, and spectral diffusion-limited homogenoeus linewidths as narrow as 4.8(3) MHz in the as-grown material. We test annealing of the Er:CeO$_2$ films up to 900 deg C, which yields modest narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%. We have also studied the variation of the optical properties as a function of Er doping and find that the results are consistent with the trends expected from inter-dopant charge interactions.

cond-mat.mtrl-sci↗

arXiv2023

Optical and spin coherence of Er$^{3+}$ in epitaxial CeO$_2$ on silicon

Solid-state atomic defects with optical transitions in the telecommunication bands, potentially in a nuclear spin free environment, are important for applications in fiber-based quantum networks. Erbium ions doped in CeO$_2$ offer such a desired combination. Here we report on the optical homogeneous linewidth and electron spin coherence of Er$^{3+}$ ions doped in CeO$_2$ epitaxial film grown on a Si(111) substrate. The long-lived optical transition near 1530 nm in the environmentally-protected 4f shell of Er$^{3+}$ shows a narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 $μ$s at 3.6 K. The reduced nuclear spin noise in the host allows for Er$^{3+}$ electron spin polarization at 3.6 K, yielding an electron spin coherence of 0.66 $μ$s (in the isolated ion limit) and a spin relaxation of 2.5 ms. These findings indicate the potential of Er$^{3+}$:CeO$_2$ film as a valuable platform for quantum networks and communication applications.

quant-ph↗

arXiv2023

Nanocavity-mediated Purcell enhancement of Er in TiO$_2$ thin films grown via atomic layer deposition

The use of trivalent erbium (Er$^{3+}$), typically embedded as an atomic defect in the solid-state, has widespread adoption as a dopant in telecommunications devices and shows promise as a spin-based quantum memory for quantum communication. In particular, its natural telecom C-band optical transition and spin-photon interface makes it an ideal candidate for integration into existing optical fiber networks without the need for quantum frequency conversion. However, successful scaling requires a host material with few intrinsic nuclear spins, compatibility with semiconductor foundry processes, and straightforward integration with silicon photonics. Here, we present Er-doped titanium dioxide (TiO$_2$) thin film growth on silicon substrates using a foundry-scalable atomic layer deposition process with a wide range of doping control over the Er concentration. Even though the as-grown films are amorphous, after oxygen annealing they exhibit relatively large crystalline grains, and the embedded Er ions exhibit the characteristic optical emission spectrum from anatase TiO$_2$. Critically, this growth and annealing process maintains the low surface roughness required for nanophotonic integration. Finally, we interface Er ensembles with high quality factor Si nanophotonic cavities via evanescent coupling and demonstrate a large Purcell enhancement (300) of their optical lifetime. Our findings demonstrate a low-temperature, non-destructive, and substrate-independent process for integrating Er-doped materials with silicon photonics. At high doping densities this platform can enable integrated photonic components such as on-chip amplifiers and lasers, while dilute concentrations can realize single ion quantum memories.

cond-mat.mtrl-sci↗