arXiv subjects

Samuele Altilia

Publications and source records attributed to Samuele Altilia.

6 recordsLinked to original sources

arXiv2026

A Simple and Robust Balanced Homodyne Detector for High-Repetition-Rate Pulsed Sources

We design and experimentally characterize a balanced homodyne detector optimized for high-repetition-rate (100 MHz) pulsed optical sources. Unlike conventional transimpedance-amplifier architectures, which suffer from nonlinearities and dynamic instabilities with ultrashort pulses, our approach allows to directly amplify the photocurrent extracted at the common photodiode node without feedback loops. A theoretical model describing the detector response, noise, and pulse-to-pulse correlations is developed, providing quantitative predictions for the signal variance, signal-to-noise ratio (SNR), and inter-pulse correlations. Implemented with two matched InGaAs photodiodes illuminated by a 1030 nm mode-locked laser at 100 MHz, the detector exhibits excellent linearity and shot-noise-limited scaling of the signal variance with optical power. Optimizing the temporal integration window yields a maximum SNR of about 14 dB, while correlation measurements confirm negligible inter-pulse correlations. These results demonstrate that the proposed architecture offers a robust and simple solution for high-speed pulsed homodyne detection, suitable for quantum optics and continuous-variable quantum information applications.

physics.optics↗

arXiv2026

Experimental investigation of the effect of dispersion on squeezing generation in a synchronously pumped optical parametric oscillator

An experimental investigation of intracavity dispersion effects in a synchronously pumped optical parametric oscillator (SPOPO) is presented. A flexible setup combining spectral and phase shaping of both pump and local oscillator fields with frequency-resolved balanced homodyne detection is employed to examine how intracavity dispersion influences squeezing. Different cavity configurations with varying finesse and dispersion conditions are studied, and the squeezing is measured as a function of pump power and local oscillator bandwidth. Contrary to expectations based on existing theoretical models, the measured squeezing levels remain essentially unchanged as dispersion varies. To account for these observations, a modeling approach is introduced in which intracavity dispersion is described as an effective spectral filtering occurring at the stage of SPOPO supermode generation. Within this framework, the filtering is incorporated directly into the interaction Hamiltonian of the nonlinear process. This perspective establishes a consistent experimental benchmark for the study of dispersion in SPOPOs and underscores the importance of spectral filtering in the interpretation of multimode squeezing experiments.

physics.optics↗

arXiv2025

Generation and detection of squeezed states via a synchronously pumped optical parametric oscillator

A synchronously pumped optical parametric oscillator (SPOPO) operating at 93 MHz is used to generate squeezed states at 1035 nm. The system features a counter-propagating beam at the same wavelength as the quantum state, which simultaneously actively stabilizes the cavity and, after transmission, acts as the local oscillator for homodyne detection. By deriving the local oscillator directly from the SPOPO cavity, the setup establishes an intrinsically excellent spatial mode overlap and high interference visibility, forming a distinctive self-referenced architecture. Two spatial light modulators enable precise spectral shaping of both the pump and the local oscillator in amplitude and phase, allowing investigation of the spectral properties of the generated states. The versatility of the setup further allows exploration of different SPOPO configurations, including regimes with varied finesse and escape efficiency. Representative measurements, including homodyne traces and squeezing levels as functions of pump power and local oscillator bandwidth, demonstrate the performance of the system. Theoretical simulations based on a multimode singular-value-decomposition model reproduce well the measured dependence of squeezing on pump power and LO bandwidth, confirming the accuracy of the description and the robustness of the setup. Measured squeezing levels up to -3.3 dB are achieved, corresponding to -5.7 dB at SPOPO output, evidencing the robustness and versatility of this platform for stable pulsed squeezed-light generation and advanced quantum optical applications.

quant-ph↗

arXiv2025

A minimalist self-differencing gating scheme for dead-time-free single-photon avalanche diodes at high repetition rate

Gated quenched SPAD detectors are widely used in quantum communication and quantum computing setups employing high-repetition-rate lasers. Here, we present a novel scheme for high-repetition-rate (100 MHz) sine-wave gated SPADs, based on the self-differencing technique, which significantly simplifies previous designs while offering additional advantages. These include straightforward implementation, more precise control of the SPAD biasing, and an improved SNR. We implemented this approach using an InGaAs photodiode and characterized it experimentally with 100 MHz attenuated laser pulses, measuring quantum efficiency, dark count rate, and afterpulsing behavior. Importantly, we demonstrate that the detector recovers full quantum efficiency in less than one pulse-repetition period after a detection event, enabling continuous operation at 100 MHz, which, in principle, could reach the GHz regime.

quant-ph↗

arXiv2025

Measuring spatial coherence of quantum and classical light with an ultrastable monolithic interferometer

We describe a monolithic interferometer for spatial coherence measurements of both classical and quantum light sources. The design combines parametric down-conversion with a thermal source, using two identical calcite crystals to control beam alignment via birefringence. The monolithic structure ensures inherent stability. Spatial coherence is measured through temporal interferograms and spectral analysis, with both methods showing close agreement with theoretical predictions. The system is robust and performs reliably for both quantum and classical light. Its design enables automated, rapid coherence measurements across different source types.

quant-ph↗

arXiv2023

Local discrimination of orbital angular momentum in entangled states

We address the use of a calcite crystal-based local detector to the discrimination of orbital angular momentum of quantum radiation produced by parametric down conversion. We demonstrate that a discrimination can be obtained exploiting the introduction of a fine and controlled spatial shift between two replicas of the state in the crystals. We believe that this technology could be used for future development of long-distance quantum communication techniques, where information encoding is based on orbital angular momentum.

quant-ph↗