Recent advances in quantum photonics have enabled increasingly robust protocols in optical phase estimation, achieving precisions beyond the standard quantum limit and approaching the Heisenberg limit. While intrinsic losses hinder the realization of unconditional super-sensitivity, reaching quantum advantage, defined as sensitivity surpassing that of any classical counterpart with identical resources, remains achievable. Here we experimentally demonstrate such an advantage using a fully fibered Mach-Zehnder-type interferometer operating at telecom wavelengths, free of post-selection. The scheme relies on the conversion of polarization-entangled photon pairs, a degree of freedom commonly favored for experimental convenience, into energy-time entanglement, which is particularly well suited for scalable fiber-based sensors. All system imperfections, including asymmetric losses and detector inefficiencies, are accounted for in the Fisher information analysis, yielding a measured quantum advantage of 10

Chromatic dispersion critically impacts the performance of numerous applications, ranging from telecommunication links to ultrafast optics and nonlinear devices, yet fast and precise measurements are challenging, especially for short length-dispersion products. We present a fully fiber-integrated nonlinear Sagnac interferometer that exploits cascaded second-order processes to generate frequency-anticorrelated idler light and achieve odd-order dispersion cancellation without active stabilization. The measurement is intrinsically self-referenced, as the dispersion-induced phase is extracted from the interference between counter-propagating nonlinear processes within the same Sagnac loop, eliminating the need for an external reference arm or prior calibration. Operating entirely at telecom wavelengths and read out on a standard optical spectrum analyzer, the device produces instantaneous, high-visibility fringes and calibration-free spectra using dual-port normalization. We demonstrate chromatic dispersion measurements on fiber samples ranging from 25 cm to 4 km, spanning short fiber segments to long-haul links. This architecture combines self-stability, broadband compatibility, and rapid acquisition, offering a practical metrology tool for both research and industry.

We report a direct demonstration of quantum-enhanced sensing in the Fourier domain by comparing single- and two-photon interference in a fiber-based interferometer under strictly identical noise conditions. The simultaneous acquisition of both signals provides a common-mode reference that enables a fair and unambiguous benchmark of quantum advantage. Spectral analysis of the interferometric outputs reveals that quantum correlations do not increase the amplitude of the modulation peak, but instead lower the associated noise floor, resulting in the expected 3 dB improvement in signal-to-noise ratio. This enhancement persists in the sub-shot-noise regime, where the classical signal becomes buried in the spectral background while the two-photon contribution remains resolvable. These observations establish Fourier-domain quantum super-sensitivity as an operational and broadly applicable resource for precision interferometric sensing.

The Talbot effect – a near-field diffraction phenomenon in which a periodic wavefront self-images at regular distances – can be transposed to the time–frequency domain via the space–time duality between diffraction and dispersive broadening. We exploit this analogy to define the time–frequency (TF) Talbot effect and show that it implements different Clifford operations on TF Gottesman-Kitaev-Preskill (TF-GKP) qubits (Phys. Rev. 102, 012607), a class of qubit states encoded in the discretised frequency and time-of-arrival degrees of freedom of entangled photon pairs, whose logical basis corresponds to even and odd components of an entangled frequency combs. These states are intrinsically robust against small frequency and temporal displacements, which can be further corrected by linear or nonlinear quantum error-correction schemes. We analyse the role of the comb envelope and peak width relative to the free spectral range, and show that a compromise must be made between the gate fidelity of the Clifford gates induced by TF-Talbot operation and the error-correction capacity of the code. We then demonstrate that the signature of the TF-Talbot effect is directly accessible via the generalised Hong-Ou-Mandel interferometer: all six logical GKP states can be unambiguously distinguished by introducing a frequency shift of half the comb periodicity in one interferometer arm. We conclude with a feasibility analysis based on current experimental technology, identifying the comb finesse as the key figure of merit for both gate performance and correctability. This conclusion extends naturally to quadrature GKP states, where a shear in quadrature phase space is precisely a Talbot effect.

Accurate knowledge of the uneven free spectral range of an optical microresonator, which provides direct insight into group velocity dispersion, is essential for understanding and controlling Kerr frequency comb dynamics. In this work, we present a simple and highly precise method for measuring the free spectral range over a 5 THz bandwidth in silicon nitride microresonators, leveraging a wavemeter with 0.4 MHz resolution. Our fully fibered plug-and-play experimental setup enables accurate extraction of resonance frequencies. By carefully analyzing the spectral position of each resonance, we measure both second- and third-order free spectral range expansion coefficients. This approach offers a robust and accessible tool for dispersion characterization in integrated photonic circuits, paving the way for next generation of Kerr comb sources and quantum photonic technologies.

Quantum-enhanced interferometry is often discussed in terms of ideal resources and asymptotic scalings, whereas in practice its performance is set by a delicate interplay between losses, state imbalance, and photon number. We address this interplay in a folded Franson interferometer fed with partially entangled N00N states, treating asymmetric losses and tunable input imbalance on equal footing. From exact detection probabilities we obtain closed-form expressions for the fringe visibility and the Fisher information, and show that these two figures of merit respond very differently to imperfections. In particular, we demonstrate that perfect interference contrast can always be recovered by compensating loss asymmetry with an appropriate input imbalance, while the Fisher information generally peaks at a distinct operating point, reflecting the irreducible trade-off between coherence restoration and signal attenuation. By determining the exact optima and benchmarking against single-photon strategies, we identify the critical loss and minimum entanglement required to maintain a genuine quantum advantage over optimized single-photon strategies under identical loss conditions, and establish their scaling with the photon number N . Beyond delineating the fundamental trade-offs between loss, entanglement, and sensitivity, this work establishes a comprehensive theoretical framework that both underpins and extends the experimental demonstration of quantum advantage reported in [1], providing a unified description of the relevant operating regimes.

Quantum frequency converters are key enabling technologies in photonic quantum information science to bridge the gap between quantum emitters and telecom photons. Here, we report a coherent frequency converter scheme combining a fiber-coupled nonlinear optical lithium niobate waveguide with a fiber-pigtailed single-photon source based on semiconductor quantum dots. Single and indistinguishable photons are converted from 925.7 nm to the telecommunication C-band, with a 48.4% end-to-end efficiency and full preservation of single-photon purity and indistinguishability. The integration of the two fiber-based modules achieving top-level performance represents an important step toward the practical interconnection of future quantum information processing systems operating at different wavelengths.

Fiber-optic resonator sensors enable high-sensitivity measurements of various physical parameters. Here, we demonstrate a quantum-enhanced interrogation scheme of an all-fiber-optic Fabry-Pèrot resonator, employing entangled two-photon interference to probe directly strain-induced optical phase shifts. The resonator is interrogated by a narrow-linewidth laser frequency-locked to its resonance mode, thereby exploiting the cavity’s inherent sensitivity to variations in the fiber length and refractive index. To access the phase fluctuations transferred to the interrogation field due to external perturbations on the sensor, we implement an in-fiber Mach–Zehnder interferometer readout. This configuration allows the sensor to operate both with classical coherent light and with entangled photon pairs generated via spontaneous parametric down-conversion. Harnessing two-photon entangled states corresponding to an N = 2 N00N state, we experimentally demonstrate a reduction of the measurement noise below the standard quantum limit. These results provide clear evidence of the quantum advantage in enhancing fiber-optic sensors under practical constraints on optical power

The interference between two independent photons stands as a crucial aspect of numerous quantum information protocols and technologies. In this work, we leverage fiber-coupled devices, which encompass fibered photon pair-sources and off-the-shelf optics, to demonstrate Hong-Ou-Mandel interference. We employ two distinct single photon sources, namely a heralded single-photon source and a weak coherent laser source, both operating asynchronously in continuous-wave regime. We record two-photon coincidences, showing a state-of-art visibility of 91.9(5)%. This work, compliant with telecom technology, provides realistic backbones for establishing long-range communication based on quantum teleportation in hybrid quantum networks.

This experimental work demonstrates multipartite quantum correlation in bright frequency combs out of a microresonator integrated on silicon nitride operating above its oscillation threshold. Multipartite features, going beyond so far reported two-mode correlation, naturally arise due to a cascade of nonlinear optical processes, making a single-color laser pump sufficient to initiate their generation. Our results show the transition from two-mode to multipartite correlation, witnessed by noise reductions as low as −2.5dB and −2dB, respectively, compared to corresponding classical levels. A constant of the movement of the nonlinear interaction Hamiltonian is identified and used to asses the multipartite behavior. Reported demonstrations pave the way to next generation on-chip multipartite sources for quantum technologies applications.

Inertial sensors, such as gyroscopes and accelerometers, are widely used in aerospace and navigation and play a vital role in seismic monitoring and safety for urban areas and large infrastructures. In particular, fiber-optic inertial sensors, being passive, lightweight, and immune to electromagnetic interference, can be ideally integrated into complex structures for localized and distributed sensing. Optical fibers are also a well-established technology, today widely used in a wealth of applications in physics, engineering and aerospace. However, limitations due to classical noise prevent a significant improvement in the performance currently achievable with fiber sensors.

Quantum interferometry methods exploit quantum resources, such as photonic entanglement, to enhance phase estimation beyond classical limits. Nonlinear optics has served as a workhorse for the generation of entangled photon pairs, ensuring both energy and phase conservation, but at the cost of limited rate and degraded signal-to-noise ratio compared to laser-based interferometry approaches. We present a “quantum-like” nonlinear optical method that reaches super-resolution in classical detection regime. This is achieved by replacing photon-pairs by coherent states of light, mimicking quantum properties through classical nonlinear optics processes. Our scheme utilizes two high-brightness lasers. This results in a substantially greater signal-to-noise ratio compared to its quantum counterpart. Such an approach paves the way to significantly reduced acquisition times, providing a pathway to explore signals across a broader range of bandwidth. The need to increase the frequency bandwidth of the quantum sensor significantly motivates the potential applications of this pathway.

We show several quantum-sensing experimental realizations dedicated to the qualification of optical-material key-properties, such as chromatic dispersion and refractive index variations. More specifically, the material under test (typically, an optical fibre or a nonlinear crystal) is introduced in one of the two arms or in the loop of interferometric devices, mainly in Mach-Zehnder and Sagnac configurations. Probing such devices using peculiar quantum, or quantum-mimicking, photonic states creates material-under-test-dependent relative-phase differences that are imprinted on the established coherent superposition. Here, the employed photonic states exhibit specific modal structures, in the frequency and/or spatial domains, that exploit or mimic quantum entanglement, providing access to the relative phases and to the optical properties under investigation. Associated measurement results show unprecedented precision and/or accuracy, reduced overhead, and otherwise unreachable stability and repeatability. Such quantum interferometric methods pave the way to redefining the very way optical materials are characterized, finding repercussion in various fields ranging from fundamental optics to industry-grade developments.

We are developing integrated source-emitting photon pairs in the MIR and IR ranges. This source is the core component of a spectroscopic technique based on non-linear interferometry, which we have successfully demonstrated.

Optical phase measurements play a key role in the detection of macroscopic parameters such as position, velocity, and displacement. They also permit to qualify the microscopic properties of photonic waveguides such as polarization mode dispersion, refractive index difference, and chromatic dispersion. In the quest for ever-better measurement performance and relevance, we report a quantum nonlinear interferometer based on a Sagnac configuration allowing precise, accurate, self-stabilized, and reproductible optical phase measurement. The potential of this system is demonstrated through the measurement of second-order dispersion, namely, chromatic dispersion of a commercial dispersion-shifted fiber at telecommunication wavelength. We demonstrate a precision of 0.007%, surpassing state-of-the-art measurements by more than one order of magnitude. Additionally, the accuracy of the second-order dispersion value is determined through the measurement of the third-order dispersion, showing a quadratic error as low as 5%. Our system promises the development of photonic-based sensors enabling the measurements of optical-material properties in a user-friendly manner.

This work reports recent progress in developing silicon photonic circuits for on-chip generation and manipulation of entangled photon pairs. We successfully integrated three essential functions— photon-pair source, pump filtering, and demultiplexing—into a single silicon chip. Key performance results include a high-quality resonator (Q-factor > 100,000), pump rejection over 80 dB, and efficient signal-idler separation with minimal crosstalk (better than 40 dB). These advancements pave the way for high-brightness photon-pair generation and manipulation, beneficial for quantum applications.

We present a theoretical model of multimode quantum correlations in bright frequency combs generated in continuous-wave regime by microresonators above threshold. Our analysis shows how these correlations emerge from cascading four-wave mixing processes fed by the input pump as well as the generated bright beams. Logarithmic negativity criterion is employed to quantify entanglement between partitions of modes, demonstrating the transition from a bipartite regime just above the oscillation threshold to the multipartite one at higher input pump powers. Due to its generality, our model can be safely used to describe other kinds of non-linear χ(3) cavities.

On-chip pump rejection filters are key building blocks in a variety of applications exploiting nonlinear phenomena, including Raman spectroscopy and photon-pair generation. Ultrahigh rejection has been achieved in the silicon technology by non-coherent cascading of modal-engineered Bragg filters. However, this concept cannot be directly applied to silicon nitride waveguides as the comparatively lower index contrast hampers the suppression of residual light propagating in the orthogonal polarization, limiting the achievable rejection. Here, we propose and demonstrate a novel, to the best of our knowledge, strategy to overcome this limitation based on non-coherent cascading of the modal- and polarization-engineered Bragg filters. Based on this concept, we experimentally demonstrate a rejection exceeding 60 dB for both polarizations, with a bandwidth of 4.4 nm. This is the largest rejection reported for silicon nitride Bragg gratings supporting both polarizations.

In this paper, we introduce an all-fibered dual-comb spectrometer based on a new design of highly nonlinear fiber to efficiently convert frequency combs from 1.55 micron to 2 micron We show that our spectrometer can be used to measure absorption profiles of rovibrational transitions of CO2 and N2O molecules, and especially their collisional self-broadening coefficients. The results show very good agreement with the HITRAN database and thus further measurements have been performed on a mixture CO2 /N2O to measure the broadening of the CO2 absorption lines resulting from the presence of N2O.