arXiv subjects

Maja Colautti

Publications and source records attributed to Maja Colautti.

14 recordsLinked to original sources

arXiv2026

Design of monolithic microcavities for enhancing organic quantum emitters

Single organic molecules are a well-established platform for high-quality single-photon generation: they can emit lifetime-limited photons with high purity and indistinguishability. However, their emission is accompanied by a pronounced red-shifted phonon sideband and higher-order vibrational peaks, which reduce the fraction of photons emitted into the desired narrowband zero-phonon line. The standard approach to suppressing this unwanted emission is to integrate the emitter into a monolithic photonic nanostructure that provides Purcell enhancement. However, incorporating organic materials using clean-room techniques has proven challenging, and has in fact so far prevented their integration into monolithic microcavities altogether. As a result, efficient, narrowband organic single-photon sources for applications in quantum information processing have remained elusive despite their considerable promise. Here, we propose three monolithic microcavity designs tailored to provide sufficient Purcell enhancement for organic quantum emitters. The Purcell effect induced by these cavities preferentially enhances emission into the 0-0 zero-phonon line, increasing spectral purity, photon extraction, and shortening the excited-state lifetime, which in turn relaxes the requirements for generating indistinguishable photons. The cavities have been optimized using Bayesian optimization and the adaptive Antoulas-Anderson (AAA) algorithm for rational approximation, which offer global optimization and the efficient reconstruction of spectra from scattering simulations, respectively. These structures are compatible with both standard clean-room processing and single-molecule preparation techniques. Therefore, they offer a clear route to realize high-quality, practically monochromatic organic single-photon light sources.

quant-ph↗

arXiv2026

Lattice quantum electrodynamics of a molecular emitter in a topological gap

Engineering the photonic environment using lattices of coupled resonators, which we refer to as lattice quantum electrodynamics (QED), provides a route to control both the spontaneous emission of individual quantum emitters and the photon-mediated interactions between them. Here we introduce an optical lattice QED platform based on individual dibenzoterrylene (DBT) molecules embedded in anthracene crystals and coupled to lattices of open optical microcavities. This hybrid architecture benefits from narrow-linewidth molecular emitters, site-resolved optical access, engineered coupled-resonator bands, and compatibility with established molecular frequency-tuning techniques. As a proof-of-principle demonstration, we observe emitter-photon bound states formed when the optical transition of a single molecule is tuned to the band gap of a Su-Schrieffer-Heeger (SSH) cavity lattice. These in-gap states display directional localization and photon emission on a single sublattice, inherited from the vacancy-induced topological edge modes of the underlying SSH lattice. Our results establish open-cavity lattices coupled to DBT molecules as a versatile architecture for engineering many-emitter quantum optical systems with controllable photon-mediated interactions.

quant-ph↗

arXiv2025

Physics-Constrained Neural Network for Metasurface Optical Response Prediction

A physics-constrained neural network is presented for predicting the optical response of metasurfaces. Our approach incorporates physical laws directly into the neural network architecture and loss function, addressing critical challenges in the modeling of metasurfaces. Unlike methods that require specialized weighting strategies or separate architectural branches to handle different data regimes and phase wrapping discontinuities, this unified approach effectively addresses phase discontinuities, energy conservation constraints, and complex gap-dependent behavior. We implement sine-cosine phase representation with Euclidean normalization as a non-trainable layer within the network, enabling the model to account for the periodic nature of phase while enforcing the mathematical constraint $\sin^2 \phi + \cos^2 \phi = 1$. A Euclidean distance-based loss function in the sine-cosine space ensures a physically meaningful error metric while preventing discontinuity issues. The model achieves good, consistent performance (e.g., coefficient of determinations above 0.9) with small, imbalanced datasets of 580 and 1075 data points, compared to several thousand typically required by alternative approaches. This physics-informed approach preserves physical interpretability while reducing reliance on large datasets and could be extended to systems involving periodic or wrapped quantities.

physics.optics↗

arXiv2025

Hybrid interfaces at the single quantum level in fluorescent molecules

We theoretically investigate a single fluorescent molecule as a hybrid quantum optical device, in which multiple external laser sources exert control of the vibronic states. In the high-saturation regime, a coherent interaction is established between the vibrational and electronic degrees of freedom, and molecules can simulate several cavity QED models, whereby a specific vibrational mode plays the role of the cavity mode. Focusing on the specific example where the system is turned into an analogue simulator of the quantum Rabi model, the steady state exhibits vibrational bi-modality resulting in a statistical mixture of highly non-classical vibronic cat states. Applying our paradigm to molecules with prominent spatial asymmetry and combining an optical excitation with a THz(IR) driving, the system can be turned into a single photon transducer. Two possible implementations are discussed based on the coupling to a subwavelength THz patch antenna or a resonant metamaterial. In a nutshell, this work assesses the role of molecules as an optomechanical quantum toolbox for creating hybrid entangled states of electrons, photons, and vibrations, hence enabling frequency conversion over very different energy scales.

quant-ph↗

arXiv2024

Enhanced control of single-molecule emission frequency and spectral diffusion

The Stark effect provides a powerful method to shift the spectra of molecules, atoms and electronic transitions in general, becoming one of the simplest and most straightforward way to tune the frequency of quantum emitters by means of a static electric field. At the same time, in order to reduce the emitter sensitivity to charge noise, inversion symmetric systems are typically designed, providing a stable emission frequency, with a quadratic-only dependence on the applied field. However, such nonlinear behaviour might reflect in correlations between the tuning ability and unwanted spectral fluctuations. Here, we provide experimental evidence of this trend, using molecular quantum emitters in the solid state cooled down to liquid helium temperatures. We finally combine the electric field generated by electrodes, which results parallel to the molecule induced dipole, to optically excite long-lived charge states, acting in the perpendicular direction. Based on the anisotropy of the molecule's polarizability, our two-dimensional control of the local electric field allows not only to tune the emitter's frequency but also to sensibly suppress the spectral instabilities associated to field fluctuations.

quant-ph↗

arXiv2024

Advances in quantum metrology with dielectrically structured single photon sources based on molecules

In the realm of fundamental quantum science and technologies, non-classical states of light, such as single-photon Fock states, are widely studied. However, current standards and metrological procedures are not optimized for low light levels. Progress in this crucial scientific domain depends on innovative metrology approaches, utilizing reliable devices based on quantum effects. We present a new generation of molecule-based single photon sources, combining their integration in a polymeric micro-lens with pulsed excitation schemes, thereby realizing suitable resources in quantum radiometry. Our strategy enhances the efficiency of generated single photon pulses and improves stability, providing a portable source at 784.7 nm that maintains consistent performance even through a cooling and heating cycle. The calibration of a single photon avalanche detector is demonstrated using light sources with different photon statistics, and the advantages of the single-molecule device are discussed. A relative uncertainty on the intrinsic detection efficiency well below 1 % is attained, representing a new benchmark in the field.

quant-ph↗

arXiv2023

Singular Spectrum Analysis of Two Photon Interference from Distinct Quantum Emitters

Two-photon interference underlies the functioning of many quantum photonics devices. It also serves as the prominent tool for testing the indistinguishability of distinct photons. However, as their time-spectral profile becomes more involved, extracting relevant parameters, foremost the central frequency difference, may start suffering difficulties. In a parametric approach, these arise from the need for an exhaustive model combined with limited count statistics. Here we discuss a solution to curtail these effects on the evaluation of frequency separation relying on a semiparametric method. The time trace of the quantum interference pattern of two photons from two independent solid-state emitters is preprocessed by means of singular spectral analysis before inspecting its spectral content. This approach allows to single out the relevant oscillations from both the envelope and the noise, without resorting to fitting. This opens the way for robust and efficient on-line monitoring of quantum emitters.

quant-ph↗

arXiv2022

Efficient room-temperature molecular single-photon sources for quantum key distribution

Quantum Key Distribution (QKD) allows the distribution of cryptographic keys between multiple users in an information-theoretic secure way, exploiting quantum physics. While current QKD systems are mainly based on attenuated laser pulses, deterministic single-photon sources could give concrete advantages in terms of secret key rate (SKR) and security owing to the negligible probability of multi-photon events. Here, we introduce and demonstrate a proof-of-concept QKD system exploiting a molecule-based single-photon source operating at room temperature and emitting at 785nm. With an estimated SKR of 0.5 Mbps, our solution paves the way for room-temperature single-photon sources for quantum communication protocols.

quant-ph↗

arXiv2021

Indistinguishable photons on demand from an organic dye molecule

Single molecules in solid-state matrices have been proposed as sources of single-photon Fock states back 20 years ago. Their success in quantum optics and in many other research fields stems from the simple recipes used in the preparation of samples, with hundreds of nominally identical and isolated molecules. Main challenges as of today for their application in photonic quantum technologies are the optimization of light extraction and the on-demand emission of indistinguishable photons. We here present Hong-Ou-Mandel experiments with photons emitted by a single molecule of dibenzoterrylene in an anthracene nanocrystal at 3 K, under continuous wave and also pulsed excitation. A detailed theoretical model is applied, which relies on independent measurements for most experimental parameters, hence allowing for an analysis of the different contributions to the two-photon interference visibility, from residual dephasing to spectral filtering.

quant-ph↗

arXiv2020

Laser-induced frequency tuning of Fourier-limited single-molecule emitters

The local interaction of charges and light in organic solids is the basis of distinct and fundamental effects. We here observe, at the single molecule scale, how a focused laser beam can locally shift by hundreds-time their natural linewidth and in a persistent way the transition frequency of organic chromophores, cooled at liquid helium temperatures in different host matrices. Supported by quantum chemistry calculations, the results are interpreted as effects of a photo-ionization cascade, leading to a stable electric field, which Stark-shifts the molecular electronic levels. The experimental method is then applied to a common challenge in quantum photonics, i.e. the independent tuning and synchronization of close-by quantum emitters, which is desirable for multi-photon experiments. Five molecules that are spatially separated by about 50 microns and originally 20 GHz apart are brought into resonance within twice their linewidth. Combining this ability with an emission linewidth that is only limited by the spontaneous decay, the system enables fabrication-free, independent tuning of multiple molecules integrated on the same photonic chip.

quant-ph↗

arXiv2020

Narrow Line Width Quantum Emitters in an Electron-Beam-Shaped Polymer

Solid-state single photon sources (SPSs) with narrow line width play an important role in many leading quantum technologies. Within the wide range of SPSs studied to date, single fluorescent molecules hosted in organic crystals stand out as bright, photostable SPSs with a lifetime-limited optical resonance at cryogenic temperatures. Furthermore, recent results have demonstrated that photostability and narrow line widths are still observed from single molecules hosted in a nanocrystalline environment, which paves the way for their integration with photonic circuitry. Polymers offer a compatible matrix for embedding nanocrystals and provide a versatile yet low-cost approach for making nanophotonic structures on chip that guide light and enhance coupling to nanoscale emitters. Here, we present a deterministic nanostructuring technique based on electron-beam lithography for shaping polymers with embedded single molecules. Our approach provides a direct means of structuring the nanoscale environment of narrow line width emitters while preserving their emission properties.

physics.app-ph↗

arXiv2019

Quantum optics with single molecules in a three-dimensional polymeric platform

The successful development of future photonic quantum technologies heavily depends on the possibility of realizing robust, reliable and, crucially, scalable nanophotonic devices. In integrated networks, quantum emitters can be deployed as single-photon sources or non-linear optical elements, provided their transition linewidth is broadened only by spontaneous emission. However, conventional fabrication approaches are hardly scalable, typically detrimental for the emitter coherence properties and bear limitations in terms of geometries and materials. Here we introduce an alternative platform, based on molecules embedded in polymeric photonic structures. Three-dimensional patterns are achieved via direct laser writing around selected molecular emitters, which preserve near-Fourier-limited fluorescence. By using an integrated polymeric design, record-high photon fluxes from a single cold molecule are reported. The proposed technology allows to conceive a novel class of quantum devices, including integrated multi-photon interferometers, arrays of indistinguishable single photon sources and hybrid electro-optical nanophotonic devices.

physics.app-ph↗

arXiv2019

A Molecule-Based Single-Photon Source Applied in Quantum Radiometry

Single photon sources (SPSs) based on quantum emitters hold promise in quantum radiometry as metrology standard for photon fluxes at the low light level. Ideally this requires control over the photon flux in a wide dynamic range, sub-Poissonian photon statistics and narrow-band emission spectrum. In this work, a monochromatic single-photon source based on an organic dye molecule is presented, whose photon flux is traceably measured to be adjustable between 144 000 and 1320 000 photons per second at a wavelength of (785.6 +/- 0.1) nm, corresponding to an optical radiant flux between 36.5 fW and 334 fW. The high purity of the single-photon stream is verified, with a second-order autocorrelation function at zero time delay below 0.1 throughout the whole range. Featuring an appropriate combination of emission properties, the molecular SPS shows here application in the calibration of a silicon Single-Photon Avalanche Detector (SPAD) against a low-noise analog silicon photodiode traceable to the primary standard for optical radiant flux (i.e. the cryogenic radiometer). Due to the narrow bandwidth of the source, corrections to the SPAD detection efficiency arising from the spectral power distribution are negligible. With this major advantage, the developed device may finally realize a low-photon-flux standard source for quantum radiometry.

quant-ph↗

arXiv2017

Photostable single-photon emission from self-assembled nanocrystals of polycyclic aromatic hydrocarbons

Quantum technologies could largely benefit from the control of quantum emitters in sub-micrometric size crystals. These are naturally prone to the integration in hybrid devices, including heterostructures and complex photonic devices. Currently available quantum emitters sculpted in nanocrystals suffer from spectral instability, preventing their use as single photon sources e.g., for most quantum optics operations. In this work we report on unprecedented performances of single-photon emission from organic nanocrystals (average size of hundreds \SI{}{\nano\meter}), made of anthracene (Ac) and doped with dibenzoterrylene (DBT) molecules. The source has hours-long photostability with respect to frequency and intensity, both at room and at cryogenic temperature. When cooled down to \SI{3}{K}, the 00-zero phonon line shows linewidth values (\SI{50}{MHz}) close to the lifetime-limit. Such optical properties in a nanocrystalline environment make the proposed organic nanocrystals a unique single-photon source for integrated photonic quantum technologies.

physics.app-ph↗