arXiv subjects

Oscar Cordero

Publications and source records attributed to Oscar Cordero.

3 recordsLinked to original sources

arXiv2026

Phase-Sensitive Crystal-Edge Effects in Linear Optical Parametric Oscillators: Why Nominally Identical Squeezers Behave Differently

Efficient and reproducible squeezed-light sources are essential for quantum information processing and precision metrology. Compact linear standing-wave optical parametric oscillators (OPOs) are attractive because they combine low optical loss, low pump-power requirements, and large longitudinal mode spacing. In doubly resonant cavities, however, the nonlinear interaction is not determined solely by bulk phase matching: forward- and backward-generated fields recombine coherently, making the effective gain sensitive to crystal-edge termination, wavelength-dependent coating phases, and the cavity resonance condition. Here, we show that these microscopic phase contributions can produce large threshold variations between nominally similar OPOs. We combine double-pass second-harmonic generation with OPO threshold measurements to extract the relevant crystal-cavity phases and analyse three linear OPO systems. The observed devices exhibit threshold variations of up to nearly six-fold, traced to the phase-dependent nonlinear-gain envelope at accessible doubly resonant operating points. Our results establish a phase-aware framework for compact linear OPOs and provide design guidelines for reproducible low-threshold squeezed-light sources in scalable photonic quantum systems.

quant-ph↗

arXiv2025

Quantum learning advantage on a scalable photonic platform

Recent advancements in quantum technologies have opened new horizons for exploring the physical world in ways once deemed impossible. Central to these breakthroughs is the concept of quantum advantage, where quantum systems outperform their classical counterparts in solving specific tasks. While much attention has been devoted to computational speedups, quantum advantage in learning physical systems remains a largely untapped frontier. Here, we present a photonic implementation of a quantum-enhanced protocol for learning the probability distribution of a multimode bosonic displacement process. By harnessing the unique properties of continuous-variable quantum entanglement, we obtain a massive advantage in sample complexity with respect to conventional methods without entangled resources. With approximately 5 dB of two-mode squeezing -- corresponding to imperfect Einstein--Podolsky--Rosen (EPR) entanglement -- we learn a 100-mode bosonic displacement process using 11.8 orders of magnitude fewer samples than a conventional scheme. Our results demonstrate that even with non-ideal, noisy entanglement, a significant quantum advantage can be realized in continuous-variable quantum systems. This marks an important step towards practical quantum-enhanced learning protocols with implications for quantum metrology, certification, and machine learning.

quant-ph↗

arXiv2021

Equivalence regimes for geometric quantum discord and local quantum uncertainty

The concept of quantum discord aims at unveiling quantum correlations that go beyond those described by entanglement. Its original formulation [J. Phys. A 34, 6899 (2001); Phys. Rev. Lett 88, 017901 (2002)] is difficult to compute even for the simplest case of two-qubits systems. Alternative formulations have been developed to address this drawback, such as the geometric measure of quantum discord [Phys. Rev. A 87, 062303 (2013)] and the local quantum uncertainty [Phys. Rev. Lett 110, 240402 (2013)] that can be evaluated in closed form for some quantum systems, such as two-qubit systems. We show here that these two measures of quantum discord are equivalent for 2 x D dimensional bipartite quantum systems. By considering the relevant example of N00N states for phase estimation in lossy environments, we also show that both metrics of quantum discord quantify the decrease of quantum Fisher information of the phase estimation protocol. Given their ease of computation in 2 x D bipartite systems, the geometric measure of quantum discord and the local quantum uncertainty demonstrate their relevance as computable measures of quantum discord.

quant-ph↗