arXiv subjects

Aneesh Ramaswamy

Publications and source records attributed to Aneesh Ramaswamy.

8 recordsLinked to original sources

arXiv2026

Analysis of polarization drift of optical signals over deployed aerial-inground fiber connections

Polarization measurements of a classical 1550-nm signal are collected and analyzed on 15-km hybrid aerial-inground fiber connections over 11 months. The spectral area and spectral moments of mHz-resolution Fast-Fourier-Transform (FFT) of these measurements are extracted, and related to temperature, humidity, wind speed, and time of day. Spectral area correlations show a strong diurnal structure: daytime maxima align with temperatures/wind speed peaks and humidity dips, with lower levels during the night. These diurnal patterns also show seasonality, with higher mean and variance in summer than winter. A random forest regressor is used to estimate FFT features from environmental measurements, informed by a theoretical model

quant-ph↗

arXiv2026

Quantum-Classical Coexistence Network Tomography

Quantum-classical coexistence networks (QCNs) share optical fiber between quantum and classical signals via wavelength-division multiplexing, offering a practical path to quantum communication over existing telecom infrastructure. However, co- and counter-propagating classical traffic introduce distinct depolarization noise, complicating channel characterization. We develop a tomography framework that infers per-link channel parameters of a QCN from end-to-end measurements alone. We first model each coexisting fiber by decomposing the signal evolution into photon loss, successful transmission, and three direction-dependent depolarization components. We then derive closed-form link-level estimators, and extend the approach to star-topology networks through a system of multiplicative equations across end-node pairs, together with a simple classical-signal-direction-switching protocol that resolves the remaining unknowns. On single-link experimental testbed data, we recover per-link depolarization probabilities accurately, with estimated process fidelities closely tracking the Bayesian-process-tomography baseline across multiple fiber lengths and wavelengths; residual gaps reflect the depolarization-only approximation. Absent a multi-link coexistence testbed, we validate the star-network estimators on emulated paths built from measured single-link channels. We further extend the framework in two directions: (i) a channel model that factorizes the coexisting fiber into a depolarizing-with-loss signal channel and a Raman-noise-injection channel on separate optical modes -- a completely-positive, trace-preserving tensor product -- whose link observables reduce exactly to our basic model; and (ii) a generalization to arbitrary topologies via a peeling algorithm (trees) and a least-squares estimator (meshes), validated by Monte-Carlo simulations on tree and cyclic-mesh networks.

cs.IT↗

arXiv2026

Degenerate mirrorless lasing in thermal vapors

Theoretical predictions were made for the steady-state gain of an orthogonally polarized probe field in a degenerate two-level alkali atom system driven by a linearly polarized continuous-wave pump field in [Opt. Mem. Neural Networks 32 (Suppl 3), S443-S446 (2023)]. Employing linear response theory, we computed the probe absorption spectrum under conditions where the pump was detuned from resonance. The results revealed a sub-natural linewidth dispersive feature near the pump resonance, characterized by both gain and absorption. Furthermore, a distinct pure gain peak emerged at a sideband associated with a dressed-state transition. These phenomena are generally absent outside the ultracold regime due to inhomogeneous broadening, primarily from Doppler effects, which obscure the fine spectral structure. In this paper, it is demonstrated that the sideband gain peak is sustained in the warm vapor regime when both the pump Rabi frequency and detuning exceed the Doppler width, $Ω_P > Δ_P \gg Δ_{Dop}$. Our results can enable degenerate mirrorless lasing in thermal alkali atom vapors, offering a significant enhancement in the signal-to-noise ratio for fluoroscopic remote magnetic sensing applications. The theoretical model studied in this paper is also a complete description of atomic vapors with isolated $J = 2 \to J' = 3$ transitions, such as atomic samarium.

physics.atom-ph↗

arXiv2024

Electron Beam Characterization via Quantum Coherent Optical Magnetometry

We present a quantum optics-based detection method for determining the position and current of an electron beam. As electrons pass through a dilute vapor of rubidium atoms, their magnetic field perturb the atomic spin's quantum state and causes polarization rotation of a laser resonant with an optical transition of the atoms. By measuring the polarization rotation angle across the laser beam, we recreate a 2D projection of the magnetic field and use it to determine the e-beam position, size and total current. We tested this method for an e-beam with currents ranging from 30 to 110 μA. Our approach is insensitive to electron kinetic energy, and we confirmed that experimentally between 10 to 20 keV. This technique offers a unique platform for non-invasive characterization of charged particle beams used in accelerators for particle and nuclear physics research.

quant-ph↗

arXiv2024

Entanglement transfer of a Rydberg W-state to a multi-mode photonic state

A robust quantum protocol has been developed that achieves highly efficient entanglement transfer from a three-atom Rydberg system, initially in a W state (|rrg>+|rgr>+|grr>)/3^0.5, to an equivalent photonic W state (|101>+|110>+|011>)/3^0.5. The entanglement transfer is achieved by dynamically adjusting the cavity mode frequencies and modulating the coupling rates, simplifying the complex transfer process into a sequence of processes involving two-level avoided crossings. We demonstrate that entanglement transfer can be achieved using either a fully adiabatic protocol or one with controlled non-adiabatic transitions at avoided crossings, generated by continuously chirping the cavity modes. Our adiabatic protocol uses the fractional STIRAP method to facilitate the partial population transfer required for generation of the photonic W state. In comparison, the non-adiabatic protocol uses non-adiabatic transitions to achieve the required partial population transfer. Furthermore, we propose two strategies for experimental implementation of our protocols.

quant-ph↗

arXiv2023

Control with EIT: High energy charged particle detection

The strong non-linear optical response of atomic systems in electromagnetically induced transparency (EIT) states is considered as a means to detect the presence of small perturbations to steady states. For the 3-level system, expressions for the group velocity and group velocity dispersion (GVD) were derived and a quantum control protocol was established to account for the change in the chirp spectrum of a probe pulse when the steady state was perturbed. This was applied to the propagation of slow Cherenkov polaritons in the medium due to the passage of a train of high-energy charged particles (high energy particles). The choice of the initial steady state with focus on the slow light condition and strong narrowly confined dispersion, equated to the continuous trapping of Cherenkov polaritons in the medium along a narrow group cone, allowing for non-trivial fields to accumulate. Considering another medium prepared for the detection of the radiation, sweeping of the control field and detuning parameters in the field-atom parameter space showed the presence of optimal regions to maximize the first order perturbation in the coherences creating changes in the optical responses that modify the chirp spectra of probe pulses.

physics.atom-ph↗

arXiv2023

Mirrorless lasing: a theoretical perspective

Mirrorless lasing has been a topic of particular interest for about a decade due to promising new horizons for quantum science and applications. In this work, we review first-principles theory that describes this phenomenon, and discuss degenerate mirrorless lasing in a vapor of Rb atoms, the mechanisms of amplification of light generated in the medium with population inversion between magnetic sublevels within the $D_2$ line, and challenges associated with experimental realization.

quant-ph↗

arXiv2023

Chirped Fractional Stimulated Raman Adiabatic Passage

Stimulated Raman Adiabatic Passage (STIRAP) is a widely used method for adiabatic population transfer in a multilevel system. In this work, we study STIRAP under novel conditions and focus on the fractional, F-STIRAP, which is known to create a superposition state with the maximum coherence. In both configurations, STIRAP and F-STIRAP, we implement pulse chirping aiming at a higher contrast, a broader range of parameters for adiabaticity, and enhanced spectral selectivity. Such goals target improvement of quantum imaging, sensing and metrology, and broaden the range of applications of quantum control techniques and protocols. In conventional STIRAP and F-STIRAP, two-photon resonance is required conceptually to satisfy the adiabaticity condition for dynamics within the dark state. Here, we account for a non-zero two-photon detuning and present control schemes to achieve the adiabatic conditions in STIRAP and F-STIRAP through a skillful compensation of the two-photon detuning by pulse chirping. We show that the chirped configuration - C-STIRAP - permits adiabatic passage to a predetermined state among two nearly degenerate final states, when conventional STIRAP fails to resolve them. We demonstrate such a selectivity within a broad range of parameters of the two-photon detuning and the chirp rate. In the C-F-STIRAP, chirping of the pump and the Stokes pulses with different time delays permits a complete compensation of the two-photon detuning and results in a selective maximum coherence of the initial and the target state with higher spectral resolution than in the conventional F-STIRAP.

quant-ph↗