arXiv subjects

Isabelle Sagnes

Publications and source records attributed to Isabelle Sagnes.

At least 19 recordsLinked to original sources

arXiv2026

Spin-to-polarization mapping with a coherent quantum dot-cavity receiver

Coherent light-matter interfaces controllably modifying the state of a photon upon interaction with a stationary qubit are a key resource for implementing deterministic entangling gates for optical quantum technologies. This requires a one-to-one mapping between the state of the scattered photon and that of the embedded qubit. Here, we present an experimental signature of such a bijection by leveraging the spin-induced Kerr rotation present in a low-noise charged quantum dot-micropillar cavity device. Through time-resolved polarization measurements, we project the electron spin to one of its eigenstates with $95\pm2\%$ fidelity with a single reflected photon detection, and follow the subsequent spin relaxation through the detection of a second reflected photon. We demonstrate that, after a transient regime governed by the trion radiative lifetime, two orthogonal polarization states can be produced, each associated to a given spin eigenstate. While the current results are limited by a timescale competition between electron spin relaxation and trion radiative lifetime, they could be improved using hole spins displaying increased relaxation times. Our work paves the way towards deterministic logic gates exploiting this one-to-one mapping between a spin and the polarization of a scattered photon.

quant-ph↗

arXiv2026

Engineering Nanophotonic Modes via the Radiation Continuum

We demonstrate, experimentally and theoretically, a universal mechanism for combining nanophotonic modes relying on radiative-loss-mediated couplings. For the case of two modes this mechanism leads to a BIC-type phenomenon characterized by the emergence of a high-quality factor subradiant mode. This mode is experimentally observed in the mid-infrared range, in arrays of double-metal patch antennas where the radiation loss rates are controlled by the geometry of the system. As the mechanism described here is independent of the specific nature or number of the interacting modes, it can be used to combine physically different resonating structures, without requiring fine symmetry tuning or specific modal configurations, opening new opportunities for resonance-based nanophotonic devices.

physics.optics↗

arXiv2026

Plasmonic-cavity Modulator for the Mid-IR with a Semi-transparent and Nonlinear Heavily-doped Semiconductor Mirror

We present a free-space plasmonic modulator based on a single heavily-doped semiconductor layer. We investigate its ability to modulate both the linear and nonlinear response at mid-infrared frequencies slightly below the plasma frequency of the semiconductor. We demonstrate electric control of the linear transmittance and reflectance, and of the efficiency of third-harmonic generation with a field-effect gate structure. We discuss further performance optimization of the device in terms of modulation speed and depth towards a fast modulator with very simple active material requirements. Our results establish a viable route toward practical plasmonic modulators and mixers operating in the mid-infrared atmospheric window available for free-space communications at wavelengths between 8 and 12 um.

physics.optics↗

arXiv2026

Direct Orientation Contrast Imaging of Anti-Phase Domains on III-V Materials Using Scanning Electron Microscopy

Direct orientation contrast imaging of zinc-blende III-V materials is studied using scanning electron microscopy. A quantitative approach is taken using a 3 {\mu}m thick orientation-patterned GaP grown on GaAs sample, studying the anti-phase domain contrast with respect to the electron beam energy and the tilt angle. A qualitative approach is taken for III-V grown on non-polar materials with and without chemical mechanical polishing. Finally, a processing of the acquired image for GaP on Si reveals in plane preferential anti-phase boundaries.

cond-mat.mtrl-sci↗

arXiv2026

Time-Resolved dynamics of semiconductor nanolaser via four-wave mixing gating

We experimentally demonstrate the direct time-domain characterization of photonic-crystal nanolasers at telecom wavelengths using a nonlinear optical gating technique based on four-wave mixing. This approach enables the temporal characterization of the ultrafast emission dynamics under short-pulse excitation with picosecond time resolution. When a weak continuous-wave component is added to the pulsed pump, the emission becomes deterministic and the build-up time is considerably reduced. The difference between purely pulsed and hybrid excitation regimes points to the influence of pulse-to-pulse timing fluctuations. To elucidate this effect, we perform Langevin-based simulations that reproduce the experimentally observed broadening and confirm that time jitter, originating from spontaneous-emission noise near threshold, dominates the temporal dispersion. These results establish four-wave-mixing gating as a powerful method to probe nanolaser dynamics with picosecond precision.

physics.optics↗

arXiv2026

Purcell enhanced electroluminescence of a unipolar light emitting quantum device at 10 micron

Efficient generation of radiation in the mid- and far- infrared relies primarily on lasers and coherent nonlinear optical phenomena driven by lasers. This wavelength range lacks of luminescent devices because the spontaneous emission rate becomes much longer than the nonradiative energy relaxation processes and therefore emitters have to count on stimulated emission produced by linear or non-linear optical gain. However, spontaneous emission is not a fundamental property of the emitter. By engineering metamaterials composed of arrays of nano-emitters into microcavities coupled to patch antennas, we have demonstrated mid-infrared electroluminescent devices emitting a collimated beam with excellent spatial properties and a factor 100 increase in the collected power, compared to standard devices. Our results illustrate that by reshaping the photonic environment around emitting dipoles, as in the Purcell effect, it is possible to enhance the spontaneous emission and conceive efficient optoelectronic light emitting devices that operate close to the thermodynamical equilibrium as LEDs in the visible range.

quant-ph↗

arXiv2026

Integrated nano electro-optomechanical spiking neuron

Neuromorphic computing offers a pathway toward energy-efficient processing of data, yet hardware platforms combining nanoscale integration and multimodal functionality remain scarce. Here we demonstrate a gallium-phosphide electro-optomechanical spiking neuron that integrates optical and electromechanical interfaces within a single nanostructure on a silicon photonic chip operating at telecommunication wavelengths (1550 nm) and exploiting a 3 gigahertz-frequency mechanical mode. Our device displays excitable dynamics, generating optical spikes at its output, as in the spiking activity of neurons and cardiac cells and defined by the calibrated all-or-none response to external perturbations. This dynamic is consistent with the saddle-node on invariant circle scenario and associated features are demonstrated including control of excitable threshold, temporal summation and refractory period. Our device compact footprint and its CMOS-compatible platform make it well suited for edge-computing applications requiring low latency and establish a foundation for versatile brain-inspired optomechanical computing and advanced on-chip optical pulse sources.

physics.optics↗

arXiv2025

Line lasing in a two-dimensional lattice of orbital photonic resonators

The engineering of specialty lasers with unconventional mode structures is one of the modern challenges in the development of integrated coherent sources. Examples include the use of bound states in the continuum, microlasers with orbital angular momentum, Dirac-band lasers and topological lasers. In this work we engineer a two-dimensional lattice of coupled micropillars with lasing line modes. We use a convenient combination of orbital photonic modes to design photonic bands which are flat in one direction and dispersive in the perpendicular one giving rise to line lasing modes. Such an architecture opens the possibility of implementing densely packed lasing matrices in compact two dimensional lattices.

physics.optics↗

arXiv2025

Measuring non-Abelian quantum geometry and topology in a multi-gap photonic lattice

Recent discoveries in semi-metallic multi-gap systems featuring band singularities have galvanized enormous interest in particular due to the emergence of non-Abelian braiding properties of band nodes. This previously uncharted set of topological phases necessitates novel approaches to probe them in laboratories, a pursuit that intricately relates to evaluating non-Abelian generalizations of the Abelian quantum geometric tensor (QGT) that characterizes geometric responses. Here, we pioneer the direct measurement of the non-Abelian QGT. We achieve this by implementing a novel orbital-resolved polarimetry technique to probe the full Bloch Hamiltonian of a six-band two-dimensional (2D) synthetic lattice, which grants direct experimental access to non-Abelian quaternion charges, the Euler curvature, and the non-Abelian quantum metric associated with all bands. Quantum geometry has been highlighted to play a key role on macroscopic phenomena ranging from superconductivity in flat-bands, to optical responses, transport, metrology, and quantum Hall physics. Therefore, our work unlocks the experimental probing of a wide phenomenology of multi-gap systems, at the confluence of topology, geometry and non-Abelian physics.

cond-mat.mes-hall↗

arXiv2025

Accurate prediction of optical transitions in epitaxial InGaAs/InAlAs asymmetric coupled quantum well structures

Atomically-resolved Z-contrast and strain mappings are used to extract a model of the composition of an InGaAs/InAlAs asymmetric coupled quantum-well structure grown on InP using metal-organic vapor phase epitaxy. The model accounts for grading across the multiple alloy interfaces. The model is used to compute intersubband absorption in the structure. The simulation accurately predicts the experimental absorption spectrum of the structure within only a few meV, an almost ten-fold improvement over simulations using a square-band profile with nominal alloy compositions, and a significant step forward in accurate and predictive simulations of the optical properties epitaxial heterostructures for emission, modulation and detection in mid-infrared.

cond-mat.mtrl-sci↗

arXiv2025

Mid-infrared integrated resonators on a III-V platform with Q-factors beyond half a million

We demonstrate mid-IR integrated race-track resonators on a III-V semiconductor platform,InGaAs core epitaxially grown on InP. We have performed a complete characterization of the optical propagation losses at wavelength = 4.6 um and wavelength = 8.5 um, two representative wavelengths for the 1st and 2nd atmospheric transparency windows. We measured losses of 1 dB/cm (TE polarization) and 1.3 dB/cm (TM polarization) at 8.5 um. Substantially lower losses, 0.28 dB/cm, were measured at wavelength = 4.6 um (TM polarization). We then implemented racetrack resonators with straight evanescent couplers. We obtained loaded quality factors larger than 600.000 at wavelength = 4.6 um. These results are promising towards the development of non-linear mid-IR integrated devices with Q factors beyond a million, where the onset of stimulated parametric processes could be reachable.

physics.optics↗

arXiv2025

A sublattice Stokes polarimeter for bipartite photonic lattices

The concept of pseudo-spin provides a general framework for describing physical systems featuring two-component spinors, including light polarization, sublattice degrees of freedom in bipartite lattices, and valley polarization in 2D materials. In all cases, the pseudo-spin can be mapped to a Stokes vector on the Poincar\'e sphere. Stokes polarimeters for measuring the polarization of light are a powerful tool with a wide range of applications both in classical and quantum science. Generalizing Stokes polarimetry to other spinor degrees of freedom is thus a challenge of prime importance. Here, we introduce and demonstrate a Stokes polarimeter for the sublattice polarization in a bipartite photonic lattice. Our method relies on k-space photoluminescence intensity measurements under controlled phase shifts and attenuations applied independently to each sublattice. We implement our method using honeycomb arrays of coupled microcavities realizing photonic analogs of graphene and hexagonal boron nitride. Using our sublattice polarimeter, we reconstruct the Bloch modes in amplitude and phase across the Brillouin zone, achieving sub-linewidth precision in the determination of their eigenenergies, including near band touching points. This enables full access to the system Bloch Hamiltonian and quantum geometric tensor. Our approach can readily be extended to more complex systems with additional internal degrees of freedom, enabling experimental investigations of trigonal warping, Chern insulating phases, and Euler-class topology in multigap systems.

cond-mat.mes-hall↗

arXiv2025

Directional transport and nonlinear localization of light in a one-dimensional driven-dissipative photonic lattice

Photonic lattices facilitate band structure engineering, supporting both localized and extended modes through their geometric design. However, greater control over these modes can be achieved by taking advantage of the interference effect between external drives with precisely tuned phases and photonic modes within the lattice. In this work, we build on this principle to demonstrate optical switching, directed light propagation and site-specific localization in a one-dimensional photonic lattice of coupled microresonators by resonantly driving the system with a coherent field of controlled phase. Importantly, our experimental results provide direct evidence that increased driving power acts as a tuning parameter enabling nonlinear localization at frequencies previously inaccessible in the linear regime. These findings open new avenues for controlling light propagation and localization in lattices with more elaborate band structures.

physics.optics↗

arXiv2025

Monitoring the generation of photonic linear cluster states with partial measurements

Quantum states of light with many entangled photons are key resources for photonic quantum computing and quantum communication. In this work, we exploit a highly resource-efficient generation scheme based on a linear optical circuit embedding a fibered delay loop acting as a quantum memory. The single photons are generated with a bright single-photon source based on a semiconductor quantum dot, allowing to perform the entangling scheme up to 6 photons. We demonstrate $2$, $3$, $4$ and $6$-photon entanglement generation at respective rates of $6$kHz, $120$Hz, $2.2$Hz, and $2$mHz, corresponding to an average scaling ratio of $46$. We introduce a method for real-time control of entanglement generation based on partially post-selected measurements. The visibility of such measurements carries faithful information to monitor the entanglement process, an important feature for the practical implementation of photonic measurement-based quantum computation.

quant-ph↗

arXiv2025

Measurement-induced back-action in a QD-based coherent spin-photon interface

Polarization-encoded spin-photon interfaces constitute promising candidates for the development of stationary nodes used as photon receivers, for quantum communication and distributed quantum computing. Here we introduce a time-resolved tomography approach which allows observing the dynamics of an electron spin, in a semiconductor quantum dot, mapped onto the dynamics of the polarization state of reflected photons. Through a single tomography experiment, we infer all the relevant spin dynamics timescales, including precession, decoherence and relaxation times. We also demonstrate and quantify the measurement back-action induced, on the embedded spin qubit, by the detection of a single reflected photon. We show that the induced population and coherence of the spin state can be tuned by the chosen polarization basis of the measurement. The control of the photon-induced back-action on the embedded spin qubit constitutes a crucial requirement for the use of spin-photon interfaces as quantum receivers.

quant-ph↗

arXiv2025

Three-dimensional Meta-atoms for High Confinement of Mid-IR Radiation

The ability to confine photons into structures with highly sub-wavelength volumes is extremely interesting for many applications such as sensing, nonlinear optics, and strong light-matter interactions. However, their realization is increasingly difficult as the wavelength becomes shorter, due to fabrication challenges and increased metal losses. In this work, we present the first experimental characterization of three-dimensional circuit-like resonators operating in the mid-infrared. Through a combination of simulations, reflectivity measurements, and scanning near-field optical microscopy, we developed an analytical model capable of predicting the electromagnetic response of these structures based on their geometrical parameters. The design we studied offers a high degree of flexibility, enabling precise control over the resonant frequency of the various modes supported by the resonator, as well as independent control over radiative and non-radiative losses. Combined with the extreme field confinement demonstrated, these meta-atoms are highly promising for applications in detectors,

physics.optics↗

arXiv2024

High efficiency second harmonic generation in transverse orientation patterned gallium phosphide waveguides

Achieving high conversion efficiencies in second-order nonlinear optical processes is a key challenge in integrated photonics for both classical and quantum applications. This paper presents the first demonstration of Transverse Orientation-Patterned gallium phosphide (TOP-GaP) waveguides showing high-efficiency second harmonic generation. In such devices, first order modal phase matching is unlocked and optimized through the inversion of the nonlinear susceptibility along the vertical direction. We discuss here the theory behind modal phase matching in TOP structures, describe the fabrication process, and present linear and nonlinear characterizations of the TOP-GaP waveguides.

physics.optics↗

arXiv2024

Indistinguishability of remote quantum dot-cavity single-photon sources

Generating identical photons from remote emitter-based bright single-photon sources is an important step for scaling up optical quantum technologies. Here, we study the Hong-Ou-Mandel interference of photons emitted from remote sources based on semiconductor quantum dots. We make use of a deterministic fabrication technique to position the quantum dots in a spectrally resonant micropillar cavity and fine tune their operation wavelength electrically. Doing so, we can match four pairs of sources between five distinct sources, study them under various excitation schemes and measure their degree of indistinguishability. We demonstrate remote indistinguishabiltiy between 44$\pm$1% and 69$\pm$1% depending on the pair of sources and excitation conditions, record values for quantum dots in cavities. The relative contribution of pure dephasing and spectral diffusion is then analysed, revealing that the remaining distinguishability is mostly due to low frequency noise

quant-ph↗