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We utilize cavity-enhanced extinction spectroscopy to directly quantify the optical absorption of defects in MoS$_2$ generated by helium ion bombardment. We achieve hyperspectral imaging of specific defect patterns with a detection limit below 0.01% extinction, corresponding to a detectable defect density below $10^{11}$ cm$^{-2}$. The corresponding spectra reveal a broad sub-gap absorption, being consistent with theoretical predictions related to sulfur vacancy-bound excitons in MoS$_2$. Our results highlight cavity-enhanced extinction spectroscopy as efficient means for the detection of optical transitions in nanoscale thin films with weak absorption, applicable to a broad range of materials., Comment: 17 pages main manuscript, 7 pages supporting information

Four-coordinate distorted tetrahedral bis(2-iminopyrrolyl)cobalt(ii) complexes behave as Single-Ion Magnets (SIMs) in the absence of an external magnetic field.

Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground states and small zero-field splittings qualify as qubits with optical read out thanks to potentially luminescent spin-flip states. We identified two V

Metal–metal bonding is a widely studied area of chemistry1–3, and has become a mature field spanning numerous d transition metal and main group complexes4–7. By contrast, actinide–actinide bonding, which is predicted to be weak8, is currently restricted to spectroscopically detected gas-phase U2 and Th2 (refs. 9,10), U2H2 and U2H4 in frozen matrices at 6–7 K (refs. 11,12), or fullerene-encapsulated U2 (ref. 13). Furthermore, attempts to prepare thorium–thorium bonds in frozen matrices have produced only ThHn (n = 1–4)14. Thus, there are no isolable actinide–actinide bonds under normal conditions. Computational investigations have explored the probable nature of actinide–actinide bonding15, concentrating on localized σ-, π-, and δ-bonding models paralleling d transition metal analogues, but predictions in relativistic regimes are challenging and have remained experimentally unverified. Here, we report thorium–thorium bonding in a crystalline cluster, prepared and isolated under normal experimental conditions. The cluster exhibits a diamagnetic, closed-shell singlet ground state with a valence-delocalized three-centre-two-electron σ-aromatic bond16,17 that is counter to the focus of previous theoretical predictions. The experimental discovery of actinide σ-aromatic bonding adds to main group and d transition metal analogues, extending delocalized σ-aromatic bonding to the heaviest elements in the periodic table and to principal quantum number six, and constitutes a new approach to elaborate actinide–actinide bonding. A crystalline cluster exhibits thorium–thorium bonding, adding to our knowledge of actinide–actinide bonding.

We demonstrate laser-written concave hemispherical structures produced on the endfacets of optical fibers that serve as mirror substrates for tunable open-access microcavities. We achieve finesse values of up to 250, and a mostly constant performance across the entire stability range. This enables cavity operation also close to the stability limit, where a peak quality factor of $1.5\times 10^4$ is reached. Together with a small mode waist of $2.3\; \mathrm{μm}$, the cavity achieves a Purcell factor of $C \sim 2.5$, which is useful for experiments that require good lateral optical access or otherwise large separation of the mirrors. Laser-written mirror profiles can be produced with a tremendous flexibility in shape and on various surfaces, opening new possibilities for microcavities., 8 pages, 3 figures

Metal complexes of 1,2-diamidobenzenes have been long studied because of their intriguing redox properties and electronic structures. We present here a series of such complexes with 1,2-bis(sulfonamido)benzene ligands to probe the utility of these ligands for generating a large zero-field splitting (ZFS, D) in metal complexes that possibly act as single-ion magnets. To this end, we have synthesized a series of homoleptic ate complexes of the form (X)n[M{bis(sulfonamido)benzene}2] (n equals 4 minus the oxidation state of the metal), where M (Fe/Co/Ni), X [K+/(K-18-c-6)+/(HNEt3)+, with 18-c-6 = 18-crown ether 6], and the substituents (methyl and tolyl) on the ligand [bmsab = 1,2-bis(methanesulfonamido)benzene; btsab = 1,2-bis(toluenesulfonamido)benzene] were varied to analyze their effect on the ZFS, possible single-ion-magnet properties, and redox behavior of these metal complexes. A combination of X-ray crystallography, (spectro)electrochemistry, superconducting quantum interference device magnetometry, high-frequency electron paramagnetic resonance spectroscopy, and Mossbauer spectroscopy was used to investigate the electronic/geometric structures of these complexes and the aforementioned properties. These investigations show that the cobalt(II) complexes display very high negative D values in the range of -100 to -130 cm-1, and the nickel(II) complexes display very high positive D values of 76 and 58 cm-1. In addition, the cobalt(II) complexes shows barriers of 200-260 cm-1 and slow relaxation of the magnetization in the absence of an external magnetic field, underscoring the robustness of this class of complexes. The iron(II) complex exhibits a D value of -3.29 cm-1 and can be chemically oxidized to an iron(III) complex that has D = -1.96 cm-1. These findings clearly show that bis(sulfonamido)benzenes are ideally suited to stabilize ate complexes, to generate very high ZFSs at the metal centers with single-ion-magnet properties, and to induce exclusive oxidation at the metal center (for iron) despite the presence of ligands that are potentially noninnocent. Our results therefore substantially enhance the scope for this class of redox-active ligands.

Here we explore the electronic structure of the diiron complex [(dppf)Fe(CO)3]0/+ [10/+; dppf = 1,1'-bis(diphenylphosphino)ferrocene] in two oxidation states by an advanced multitechnique experimental approach. A combination of magnetic circular dichroism, X-ray absorption and emission, high-frequency electron paramagnetic resonance (EPR), and Mossbauer spectroscopies is used to establish that oxidation of 10 occurs on the carbonyl iron ion, resulting in a low-spin iron(I) ion. It is shown that an unequivocal result is obtained by combining several methods. Compound 1+ displays slow spin dynamics, which is used here to study its geometric structure by means of pulsed EPR methods. Surprisingly, these data show an association of the tetrakis[3,5-bis(trifluoromethylphenyl)]borate counterion with 1+.

We report the synthesis of the lanthanide-(bis)boryloxide complex [Dy{OB(NArCH)2}2(THF)4][BPh4] (2Dy, Ar = 2,6-Pri2C6H3), with idealised D4h@Dy(III) point-group symmetry. Complex 2Dy exhibits single-molecule magnetism (SMM), with one of the highest energy barriers (Ueff = 1565(298) K) of any six-coordinate lanthanide-SMM. Complex 2Dy validates electrostatic model predictions, informing the future design of lanthanide-SMMs.

Metallonitrenes (M–N) are complexes with a subvalent atomic nitrogen ligand that have been proposed as key reactive intermediates in nitrogen atom transfer reactions. However, in contrast to the common classes of nitride complexes (M≡N) and organic nitrenes (R–N), structurally and spectroscopically well defined ‘authentic’ metallonitrenes with a monovalent atomic nitrogen ligand remain elusive. Here we report that the photolysis of a platinum(ii) pincer azide complex enabled the crystallographic, spectroscopic, magnetic and computational characterization of a metallonitrene that is best described as a singly bonded atomic nitrogen diradical ligand bound to platinum(ii). The photoproduct exhibits selective C–H, B–H and B–C nitrogen atom insertion reactivity. Despite the subvalent metallonitrene character, mechanistic analysis for aldehyde C–H amidation shows nucleophilic reactivity of the N-diradical ligand. Ambiphilic reactivity of the metallonitrene is indicated by reactions with CO and PMe3 to form isocyanate and phosphoraneiminato platinum(ii) complexes, respectively. Transient metallonitrenes (M–N) have been proposed as key intermediates in nitrogen atom transfer reactions, but well-defined examples have remained elusive. Now, a platinum complex with an atomic nitrogen ligand, best described as a subvalent nitrogen diradical singly bonded to a platinum(ii) ion (Pt–N), has been isolated and shows ambiphilic reactivity.

We observe cavity-enhanced ensemble fluorescence of nitrogen-vacancy centers in diamond, showing Purcell-enhancement of the Zero Phonon Line (ZPL). The emission features temporal bunching of ZPL photons, indicating collective emission that can be attributed to superfluorescence.

Open-access microcavities are a powerful tool to enhance light-matter interactions for solid-state quantum and nano systems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements - full tunability to cope with spatial and spectral inhomogeneities of a material, and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully-tunable, open-access, fiber-based Fabry-P\'erot microcavity platform which can be operated also under increased noise levels in a closed-cycle cryostat. It comprises custom-designed monolithic micro- and nanopositioning elements with up to mm-scale travel range that achieve a passive cavity length stability at low temperature of only 15 pm rms in a closed-cycle cryostat, and 5 pm in a more quiet flow cryostat. This can be further improved by active stabilization, and even higher stability is obtained under direct mechanical contact between the cavity mirrors, yielding 0:8 pm rms during the quiet phase of the closed-cycle cryo cooler. The platform provides operation of cryogenic cavities with high finesse and small mode volume for strong enhancement of light-matter interactions, opening up novel possibilities for experiments with a great variety of quantum and nano materials., Comment: 7 pages, 5 figures

International audience; Rare-earth ions (REIs) are promising solid-state systems for building light-matter interfaces at the quantum level1,2. This relies on their potential to show narrow optical and spin homogeneous linewidths, or, equivalently, long-lived quantum states. This enables the use of REIs for photonic quantum technologies such as memories for light, optical-microwave transduction and computing3-5. However, so far, few crystalline materials have shown an environment quiet enough to fully exploit REI properties. This hinders further progress, in particular towards REI-containing integrated nanophotonics devices6,7. Molecular systems can provide such capability but generally lack spin states. If, however, molecular systems do have spin states, they show broad optical lines that severely limit optical-to-spin coherent interfacing8-10. Here we report on europium molecular crystals that exhibit linewidths in the tens of kilohertz range, orders of magnitude narrower than those of other molecular systems. We harness this property to demonstrate efficient optical spin initialization, coherent storage of light using an atomic frequency comb, and optical control of ion-ion interactions towards implementation of quantum gates. These results illustrate the utility of rare-earth molecular crystals as a new platform for photonic quantum technologies that combines highly coherent emitters with the unmatched versatility in composition, structure and integration capability of molecular materials.

Certain aspects before and during the fabrication of single-crystal diamond (SCD) membranes are highlighted, which are decisive to obtain high-quality membranes with low surface roughness values around 0.2 nm on a small area scale. In addition to the requirements for the starting material, including a high planarity and a moderate surface roughness, the importance of cleaning processes to minimize particles and impurities before and during the structuring is emphasized. With the help of a planarization procedure, consisting of a combination of different Ar/Cl$_2$ recipes with low etch rates, surface defects like grooves due to polishing are minimized and smooth surfaces are acquired. Severe micromasking can be prevented by the application of a cyclic Ar/Cl$_2$ + O$_2$ recipe, allowing finally the fabrication of defect-minimized and planarized SCD membranes in the thickness range between few microns and a few hundred nanometers. The high quality of the structured SCD membranes is evidenced with a morphological as well as an optical characterization via fiber-based microcavity measurements.

The fine-tuning of intermolecular or intramolecular non-covalent interactions (NCIs) and thus the precise synthesis of metal complexes in which the spin states can be controlled by NCIs remains challenging, even though several such complexes have been intensively studied. In this regard, we present mononuclear cobalt(II) and iron(II) complexes with "click"-derived tripodal ligands that contain fluorinated benzyl substituents in the secondary coordination sphere. The complexes were co-crystallized with different solvent molecules to decipher the effect of the crystallized solvents on NCIs, and on the spin state of the metal ion. Additionally, the fluorine-specific interactions in the secondary coordination sphere were examined. We present a first structure-property correlation between the nature of interaction of the (per)fluorinated aromatic substituents on the ligand periphery, and the spin state of the metal complexes. In particular, the TF5TA containing ligand show interesting stacking motifs depending on the used solvent, and these interactions have an influence on the spin state of the cobalt(II) complexes. Furthermore, the iron(II) complex thereof, Fe(TF5TA)2(BF4)2·2EtOH displays spin crossover (SCO).

Developing efficient molecular catalysts for the electrocatalytic hydrogen evolution reaction (HER) is a highly important goal in contemporary science. We report here on a bimetallic triply fused copper porphyrin complex (1) comprising two monomeric porphyrin units linked through β–β, meso–meso, β′–β′ triple covalent linkages, that exhibits remarkable enhancement of catalytic activity for the electrochemical HER in comparison to the analogous monomeric copper porphyrin complex (2). Spectroscopic characterization, in association with magnetic measurements, clearly establish the ground state structures of both the bimetallic and monometallic complexes as containing two and one copper (II) centers, respectively. The fused metalloporphyrin complex is found to undergo electrochemical reduction at a lower negative applied potential compared to the metalloporphyrin monomer, as evident from the significant anodic shift (~800mV) in the potential of the first reduction process. Electrochemical investigations in the presence of a proton source (trifluoroacetic acid) confirm that the catalytic activity of the fused metalloporphyrin occurs at a significantly lower onset potential, (overpotential decreased by ~320 mV), compared to the non-fused monomer. Controlled potential electrolysis combined with the kinetic analysis of catalysts 1 and 2 confirm the production of hydrogen, with 96% and 71% faradaic efficiencies and turnover numbers of 102 and 18, respectively. Kinetic investigations further reveal an observed rate constant of around 107 (s-1), implying high efficiency of the bimetallic catalyst towards hydrogen evolution reaction. Mechanistic insights are presented by using a combination of UV-vis-NIR and EPR spectroscopy and electrochemistry. Our results thus firmly establish the triply fused porphyrin ligands as candidates for generating highly efficient molecular electrocatalysts in combination with transition metal centers.

The use of low-dimensional objects in the field of cavity optomechanics is limited by their low scattering cross section compared to the size of the optical cavity mode. Fiber-based Fabry-P\'{e}rot microcavities can feature tiny mode cross sections and still maintain a high finesse, boosting the light-matter interaction and thus enabling the sensitive detection of the displacement of minute objects. Here we present such an ultrasensitive microcavity setup with the highest finesse reported so far in loaded fiber cavities, $\mathcal{F} = 195\,000$. We are able to position-tune the static optomechanical coupling to a silicon nitride membrane stripe, reaching frequency pull parameters of up to $\mathrm{\lvert G/2\pi\rvert=1}\,\mathrm{GHz\, nm^{-1}}$. We also demonstrate radiation pressure backaction in the regime of an ultrahigh finesse up to $\mathcal{F}=165\,000$.

The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g. for shaping the emitted photons waveform, for generating quantum entanglement, or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into nanoparticles. By embedding the doped nanoparticles into a fully tunable high finesse fiber based optical microcavity, we show that we can tune the cavity on- and out of-resonance by controlling its length with sub-nanometer precision, on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This allows us to shape in real time the Purcell enhanced emission of the ions and to achieve full control over the emitted photons' waveforms. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity., 12 pages, 7 figures, submitted

Whilst quantum computing has recently taken great leaps ahead, the development of quantum memories has decidedly lagged behind. Quantum memories are essential devices in the quantum technology palette and are needed for intermediate storage of quantum bit states and as quantum repeaters in long-distance quantum communication. Current quantum memories operate at cryogenic, mostly sub-Kelvin temperatures and require extensive and costly peripheral hardware. It is demonstrated that ensembles of weakly coupled molecular spins show long coherence times and can be used to store microwave pulses of arbitrary phase. These studies exploit strong coupling of the spin ensemble to special 3D microwave resonators. Most importantly, these systems operate at room temperature.

The first isolation and structural characterization of an f-element dinitrogen complex was reported in 1988, but an f-element complex with the first heavier group 15 homologue diphosphorus has to date remained unknown. Here, we report the synthesis of a side-on bound diphosphorus complex of uranium(IV) using a 7λ3-(dimethylamino)phosphadibenzonorbornadiene-mediated P atom transfer approach. Experimental and computational characterization reveals that the diphosphorus ligand is activated to its dianionic (P2)2- form and that in-plane U-P π-bonding dominates the bonding of the U(μ-η2:η2-P2)U unit, which is supplemented by a weak U-P interaction of δ symmetry. A preliminary reactivity study demonstrates conversion of this diphosphorus complex to unprecedented uranium cyclo-P3 complexes, suggesting in situ generation of transient, reactive phosphido species.

Here we explore the electronic structure of the diiron complex [(dppf)Fe(CO)

Realization of quantum photonic devices requires coupling single quantum emitters to the mode of optical resonators. In this work, a hybrid system consisting of defect centers in few-layer hexagonal boron nitride (hBN) grown by chemical vapor deposition and a fiber-based Fabry–Pérot cavity is presented. The sub 10-nm thickness of hBN and its smooth surface enable efficient integration into the cavity mode. This hybrid platform is operated over a broad spectral range larger than 30 nm and its tuneability is used to explore different coupling regimes. Consequently, very large cavity-assisted signal enhancement up to 50-fold and strongly narrowed linewidths are achieved, which is owing to cavity funneling, a record for hBN-cavity systems. Additionally, an excitation and readout scheme is implemented for resonant excitation that allows to establish cavity-assisted photoluminescence excitation (PLE) spectroscopy. This work marks an important milestone for the deployment of 2D materials coupled to fiber-based cavities in practical quantum technologies.

The introduction of an optical resonator can enable efficient and precise interaction between a photon and a solid-state emitter. It facilitates the study of strong light-matter interaction, polaritonic physics and presents a powerful interface for quantum communication and computing. A pivotal aspect in the progress of light-matter interaction with solid-state systems is the challenge of combining the requirements of cryogenic temperature and high mechanical stability against vibrations while maintaining sufficient degrees of freedom for in-situ tunability. Here, we present a fiber-based open Fabry-P\'{e}rot cavity in a closed-cycle cryostat exhibiting ultra-high mechanical stability while providing wide-range tunability in all three spatial directions. We characterize the setup and demonstrate the operation with the root-mean-square cavity length fluctuation of less than $90$ pm at temperature of $6.5$ K and integration bandwidth of $100$ kHz. Finally, we benchmark the cavity performance by demonstrating the strong-coupling formation of exciton-polaritons in monolayer WSe$_2$ with a cooperativity of $1.6$. This set of results manifests the open-cavity in a closed-cycle cryostat as a versatile and powerful platform for low-temperature cavity QED experiments., Comment: 10 pages, 8 figures

We report the synthesis of the lanthanide-(bis)boryloxide complex [Dy{OB(NArCH)2}2(THF)4][BPh4] (2Dy, Ar = 2,6-Pri2C6H3), with idealised D4h@Dy(iii) point-group symmetry. Complex 2Dy exhibits single-molecule magnetism (SMM), with one of the highest energy barriers (Ueff = 1565(298) K) of any six-coordinate lanthanide-SMM. Complex 2Dy validates electrostatic model predictions, informing the future design of lanthanide-SMMs.

Molecular qubits are extensively tunable, in contrast to other spin qubits. The use of spin ensembles as quantum repeaters in quantum communication relies on strong coupling between photon and spin modes. Here we show that the effective coupling strength depends on the magnetic interactions between the spins in the ensemble.

Single quantum emitters coupled to optical cavities in the Purcell regime can be used as high-efficiency spin-photon interfaces that are essential for building a quantum network. Furthermore, the dynamical control of the spontaneous emission rate of quantum emitters can have important implications in quantum technologies, e.g. for shaping the emitted photons waveform, or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical Purcell-enhanced emission of a mesoscopic ensemble of erbium ions doped into nanocrystals coupled to a fully-tunable high-finesse fiber-based optical microcavity. Erbium has excellent optical and spin coherence properties at cryogenic temperatures and, in addition, has a transition in the telecom band that can facilitate integration into existing commercial telecom fibers. We show that we can tune the cavity on and out of resonance at a rate of above 8 KHz, which is two orders of magnitude faster that the natural lifetime of the erbium ions (55 Hz), and a factor of five faster than the Purcell enhanced emission (1.8 KHz). This allows us to shape in real time the Purcell enhanced emission of the ions and to achieve full control over the emitted photon’s waveforms. With moderate improvements in our detection efficiency and cavity finesse, this capability will allow for the generation of single telecom photons with controllable wave-shape from single erbium ions and for the realization of quantum processing between rare-earth ion qubits using dipolar interactions.

The chromium(III) complex [CrIII(ddpd)2]3+ (molecular ruby; ddpd=N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine) is reduced to the genuine chromium(II) complex [CrII(ddpd)2]2+ with d4 electron configuration. This reduced molecular ruby represents one of the very few chromium(II) complexes showing spin crossover (SCO). The reversible SCO is gradual with T 1/2 around room temperature. The low‐spin and high‐spin chromium(II) isomers exhibit distinct spectroscopic and structural properties (UV/Vis/NIR, IR, EPR spectroscopies, single‐crystal XRD). Excitation of [CrII(ddpd)2]2+ with UV light at 20 and 290 K generates electronically excited states with microsecond lifetimes. This initial study on the unique reduced molecular ruby paves the way for thermally and photochemically switchable magnetic systems based on chromium complexes complementing the well‐established iron(II) SCO systems., Ruby‐reduced: Reduction of the molecular ruby [CrIII(ddpd)2]3+ (ddpd=N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine) gives the genuine chromium(II) complex [CrII(ddpd)2]2+ showing spin crossover (SCO) with T 1/2 around room temperature. Geometric distortions and color changes accompany this reversible SCO. Excitation with UV light yields electronically excited states with microsecond lifetimes.

We operate a fiberbased cavity with an inserted diamond membrane containing ensembles of silicon vacancy centers (SiV$^-$) at cryogenic temperatures $ \geq4~$K. The setup, sample fabrication and spectroscopic characterization is described, together with a demonstration of the cavity influence by the Purcell effect. This paves the way towards solid state qubits coupled to optical interfaces as long-lived quantum memories., 10 pages, 6 figures

In a Bose–Einstein condensate, bosons condense in the lowest-energy mode available and exhibit high coherence. Quantum condensation is inherently a multimode phenomenon, yet understanding of the condensation transition in the macroscopic limit is hampered by the difficulty in resolving populations of individual modes and the coherences between them. Here, we report non-equilibrium Bose–Einstein condensation of 7 ± 2 photons in a sculpted dye-filled microcavity, where the extremely small particle number and large mode spacing of the condensate allow us to measure occupancies and coherences of the individual energy levels of the bosonic field. Coherence of the individual modes is found to generally increase with increasing photon number. However, at the break-down of thermal equilibrium we observe phase transitions to a multimode condensate regime wherein coherence unexpectedly decreases with increasing population, suggesting the presence of strong intermode phase or number correlations despite the absence of a direct nonlinearity. Experiments are well-matched to a detailed non-equilibrium model. We find that microlaser and Bose–Einstein statistics each describe complementary parts of our data and are limits of our model in appropriate regimes, providing elements to inform the debate on the differences between the two concepts1,2.

Monolayer transition metal dichalcogenides integrated in optical microcavities host exciton-polaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe2-WSe2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavity – van der Waals heterostructure systems., Cavity-enhanced light-matter interaction in the weak-coupling regime is known to result in Purcell enhancement. Here the authors demonstrate Purcell enhancement in the photoluminescence of vertical MoSe2-WSe2 heterostructures coupled to a micro-cavity and determine the light-matter coupling strength for interlayer excitons.