Open Access
Generalized approach to quantum interference in lossy N-port devices via a singular value decomposition
(Optica, 2022) Hernández Martínez, Osmery; Liberal Olleta, Íñigo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Modeling quantum interference in the presence of dissipation is a critical aspect of quantum technologies. Including dissipation into the model of a linear device enables for assessing the detrimental impact of photon loss, as well as for studying dissipation-driven quantum state transformations. However, establishing the input-output relations characterizing quantum interference at a general lossy N-port network poses important theoretical challenges. Here, we propose a general procedure based on the singular value decomposition (SVD), which allows for the efficient calculation of the input-output relations for any arbitrary lossy linear device. In addition, we show how the SVD provides an intuitive description of the principle of operation of linear optical devices. We illustrate the applicability of our method by evaluating the input-output relations of popular reciprocal and nonreciprocal lossy linear devices, including devices with singular and nilpotent scattering matrices. Our method also enables the analysis of quantum interference in large lossy networks, as we exemplify with the study of an N-port epsilon-near-zero (ENZ) hub. We expect that our procedure will motivate future research on quantum interference in complex devices, as well as the realistic modelling of photon loss in linear lossy devices.
Open Access
Quantum and thermal noise in coupled non-hermitian waveguide systems with different models of gain and loss
(De Gruyter, 2025-01-03) Hernández Martínez, Osmery; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Non-Hermitian (NH) photonic systems leverage gain and loss to open new directions for nanophotonic technologies. However, the quantum and thermal noise intrinsically associated with gain/loss affects the eigenvalue/eigenvector structure of NH systems, and thus the existence of exceptional points, as well as the practical noise performance of these systems. Here, we present a comparative analysis of the impact of different gain and loss mechanisms on the noise generated in gain-loss compensated NH waveguide systems. Our results highlight important differences in the eigenvalue/eigenvector structure, noise power, photon statistics and squeezing. At the same time, we identify some universal properties such as the occurrence of phase-transition points in parameter space and intriguing phenomena related to them, including coalescence of pairs of eigenvectors, gain-loss compensation, and linear scaling of the noise with the length of the waveguide. We believe that these results contribute to a better understanding of the impact of the gain/loss mechanism on the noise generated in NH systems.
Open Access
Quantum interference in Wilkinson power dividers
(John Wiley & Sons, 2022) Hernández Martínez, Osmery; Ortega Gómez, Ángel; Bravo Acha, Mikel; Liberal Olleta, Íñigo; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
Scaling up quantum technologies entails the challenge of developing large-scale and high-performance photonic quantum networks. Engineering novel optical components, with a compact footprint and advanced functionalities, might help addressing this challenge by reducing the size and complexity of optical networks. Here, quantum interference phenomena in Wilkinson power dividers (WPDs), a popular element of microwave networks, is investigated. It is theoretically demonstrated that WPDs grant access to coherent perfect absorption (CPA) quantum state transformations (single photon CPA, coherent absorption of N00N states, two-photon nonlinear absorption, and absorption of coherence in squeezed light) in CPA networks with a smaller footprint and a reduced number of elements. Additionally, it is shown how a WPD can be designed in a pure silicon-on-insulator platform by taking advantage of radiative losses. These findings might represent an important step forward in the development of CPA quantum networks.
Open Access
On the lossy character of Y-branches and their analogy to Wilkinson power dividers
(Optica Publishing Group, 2024-11-04) Oña Valladares, Douglas; Hernández Martínez, Osmery; Ortega Gómez, Ángel; González-Andrade, David; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Y-branches are commonly used devices for power splitting and combining in various technological applications. Despite their widespread use, research on their design and analysis has been mostly focused on their characterization based on reflection and transmission when operating as power dividers, leaving aside an exhaustive consideration of all their possible modes of operation. Also, it has not been fully recognized that these devices have intrinsic losses. If these losses are not properly managed, they can negatively impact the network, but also open the door to new opportunities. In this context, this paper examines Y-bifurcation properties and their connection to Wilkinson's power dividers. Additionally, through numerical analysis, we demonstrate the possibility of integrating these devices into more complex optical networks. We use them as components in generalized power dividers and analog optical computational systems designed to filter out the maximum common phase component and avoid backward reflections for any input signal.
Open Access
Orthogonal thermal noise and transmission signals: a new coherent perfect absorption's feature
(American Physical Society, 2024-09-06) Oña Valladares, Douglas; Ortega Gómez, Ángel; Hernández Martínez, Osmery; Liberal Olleta, Íñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Coherent perfect absorption (CPA) is an interference process associated with the zeros of the scattering matrix of interest for optical computing, data processing, and sensing. However, the noise properties of CPA remain relatively unexplored. Here, we demonstrate that CPA thermal noise signals exhibit a unique property: they are orthogonal to the signals transmitted through the network. In turn, such property enables a variety of thermal noise management effects, such as the physical separability of thermal noise and transmitted signals, and "externally lossless"networks that internally host radiative heat transfer processes. We believe that our results provide a new perspective on the many CPA technologies currently under development.