arXiv subjects

Amit Kam

Publications and source records attributed to Amit Kam.

7 recordsLinked to original sources

arXiv2026

Toward Micro-Endoscopy: Distal-Free, Configuration-Agnostic Focusing Through Multimode Fiber

Multimode fibers (MMFs) can transmit multiple guided modes simultaneously, making them a promising platform for high-resolution biomedical imaging, endoscopy and high-bandwidth optical communication. However, their complex modal behavior, influenced by environmental perturbations and mode coupling, presents a major challenge for accurate wavefront control. Conventional approaches for shaping the light at their output typically rely on the transmitted field as a source for iterative feedback, making it impractical for in-situ applications where direct access to the transmission is impossible. Here, we introduce a deep learning-based framework for predicting transmission through MMF by observing only the reflected signal. Harnessing the reflected signals that encode the fiber's internal configuration, our approach not only generalizes across varying fiber conditions but also enables focusing through the fiber without requiring transmission feedback. By training the system experimentally using a dataset of 4 million images across 1200 distinct fiber configurations, we demonstrate robust and precise wavefront reconstruction even under significant perturbations. Our results underscore the potential of learning-based techniques for real-time MMF-based imaging and optical communications, paving the way for efficient non-invasive focusing in practical applications.

physics.optics↗

arXiv2026

Quantum Skyrmions in Mixed States of Light and Their Nested Topology

Topological quasiparticles of light, such as classical and quantum optical skyrmions, have so far relied on fully coherent or pure quantum states whose topology is encoded in the entanglement between polarization and two-dimensional spatial modes. Here we show that skyrmionic topology can emerge directly within the density matrix of a mixed quantum state. We introduce a framework in which a coherence-Stokes vector defines a topological texture over the density matrix, enabling the realization of quantum skyrmions using only a pseudospin and a real or synthetic one-dimensional space of modes. For a single photon, the density matrix is analogous to the coherence matrix of classical light, and can be encoded using partially coherent electromagnetic fields. We further analyze the topological texture encoded in a bipartite entangled photon pair, showing how skyrmions arise not only in the full bi-photon system, but also in its reduced subspaces with any pseudospin-mode combination simultaneously. We then explore the robustness of such skyrmions to environmental noise, and discover their persistence in mixed-quantum states of multiple photons. Finally, we propose a feasible experimental route to generate and measure such skyrmions using integrated photonic networks, and suggest avenues for similar implementations in other quantum systems. Our work paves the way for robustly encoding classical information on partially coherent light or on mixed quantum states and for encoding topological charges on many-body quantum systems.

quant-ph↗

arXiv2025

Hyperentanglement in Nanophotonic Systems with Discrete Rotational Symmetry

We propose a scheme to generate hyperentanglement between photons carrying angular momentum in nanophotonic systems with discrete rotational symmetry. Coupling free-space photons into surface plasmon polaritons by a polygonal-shaped grating restricts the basis of the generated near-field modes to a finite set, thus creating a new mechanism for spatial mode entanglement. By encoding the incoming photons with spin and orbital angular momenta, we find that the system preserves the high-dimensional Hilbert space, in contrast to rotationally symmetric nanophotonic platforms, where the inseparability of spin and orbital degrees of freedom results in loss of information. We further show that by properly engineering the phase of the photons to conform to the polygonal boundary conditions, we achieve a new scheme for generating hyperentangled states, utilizing both the vector-field nature of the nanophotonic modes and the finite basis of states in polygonal boundary conditions. Our approach paves the way for on-chip quantum communication by expanding the Hilbert space used in computation.

physics.optics↗

arXiv2025

Reduced State Embedding for Error Correction in Quantum Cryptography

Encoding in a high-dimensional Hilbert space improves noise resilience in quantum information processing. This approach, however, may result in cross-mode coupling and detection complexities, thereby reducing quantum cryptography performance. This fundamental trade-off between correctness and secrecy motivates the search for quantum error-correction approaches for cryptography. Here, we introduce state embeddings that use a k-symbol subset within a d-dimensional Hilbert space, tailored to the channel's error structure. In the framework of quantum error-correction, our reduced-state embedding realizes an explicit erasure-type error-correction within the quantum channel. We demonstrate the advantage of our scheme in realistic quantum channels, producing a higher secure key rate. We validate our approach using a d=25 quantum key distribution (QKD) experimental data, derive closed-form expressions for the key rate and threshold, and determine the optimum at k=5. These findings advance high-dimensional QKD and pave the way to error-correction and modulation for quantum cryptography.

quant-ph↗

arXiv2025

Tracking the Evolution of Near-Field Photonic Qubits into High-Dimensional Qudits via State Tomography

Quantum nanophotonics offers essential tools and technologies for controlling quantum states, while maintaining a miniature form factor and high scalability. For example, nanophotonic platforms can transfer information from the traditional degrees of freedom (DoFs), such as spin angular momentum (SAM) and orbital angular momentum (OAM), to the DoFs of the nanophotonic platform - and back, opening new directions for quantum information processing. Recent experiments have utilized the total angular momentum (TAM) of a photon as a unique means to produce entangled qubits in nanophotonic platforms. Yet, the process of transferring the information between the free-space DoFs and the TAM was never investigated, and its implications are still unknown. Here, we reveal the evolution of quantum information in heralded single photons as they couple into and out of the near-field of a nanophotonic system. Through quantum state tomography, we discover that the TAM qubit in the near-field becomes a free-space qudit entangled in the photonic SAM and OAM. The extracted density matrix and Wigner function in free-space indicate state preparation fidelity above 97%. The concepts described here bring new concepts and methodologies in developing high-dimensional quantum circuitry on a chip.

quant-ph↗

arXiv2025

Nonlinear Nanophotonics for High-Dimensional Quantum States

Quantum nanophotonics merges the precision of nanoscale light manipulation with the capabilities of quantum technologies, offering a pathway for enhanced light-matter interaction and compact realization of quantum devices. Here, we show how a recently-demonstrated nonlinear nanophotonic process can be employed to selectively create photonic high-dimensional quantum states (qudits). We utilize the nonlinearity on the surface of the nanophotonic device to dress, through the polarization of the pump field, the near-field modes carrying angular momentum and their superpositions. We then use this approach for the realization of a multilevel quantum key distribution protocol, which doubles the key rate compared to standard schemes. This idea is an important step towards experimental realizations of quantum state generation and manipulation through nonlinearity within nanophotonic platforms, and enables new capabilities for on-chip quantum devices.

physics.optics↗

arXiv2023

Time-refraction and time-reflection above critical angle for total internal reflection

We study the time-reflection and time-refraction of waves caused by a spatial interface with a medium undergoing a sudden temporal change in permittivity. We show that monochromatic waves are transformed into a pulse by the permittivity change, and that time-reflection is enhanced at the vicinity of the critical angle for total internal reflection. In this regime, we find that the evanescent field is transformed into a propagating pulse by the sudden change in permittivity. These effects display enhancement of the time-reflection and high sensitivity near the critical angle, paving the way to experiments on time-reflection and photonic time-crystals at optical frequencies

physics.optics↗