arXiv subjects

Leif Bauer

Publications and source records attributed to Leif Bauer.

14 recordsLinked to original sources

arXiv2026

Hybrid Ferromagnet-SNSPDs: Single photon induced order-to-disorder transition in ferromagnets coupled to thin film superconductors

The development of midwave and longwave infrared single photon detectors is crucial for their emerging applications in spectroscopy, remote sensing, exoplanet detection, and free space quantum communications. However, existing sensors need to be operated at extremely low temperatures (0.08-0.9K) to reduce dark noise and hence require the use of advanced cryogenics such as dilution refrigerators or $^3$He cryogens, significantly limiting applications. Here we propose a vortex-engineering approach based on a hybrid phase transition in a ferromagnet/superconductor bilayer to increase the operating temperature of infrared single photon detectors up to 3.75K. We show that the introduction of a ferromagnetic layer produces a local magnetic field which impedes vortex crossing in the superconductor, reducing dark noise. When a single photon is incident, the photon-induced hotspot causes an order-to-disorder transition in the ferromagnet, leading to a vortex-induced phase transition in the superconducting layer. By engineering the ferromagnet's Curie temperature to be close to the device's operating temperature, single photon sensitivity can be achieved at increased operating temperatures. We predict at midwave/longwave infrared wavelengths (3-14$\mu$m) the operating temperature can be raised to 3.25-3.75K, enabling significantly simpler cooling systems.

cond-mat.supr-con↗

arXiv2026

Physics-Integrated Inference for Signal Recovery in Non-Gaussian Regimes

High-performance room-temperature sensing is often limited by non-stationary $1/f$ fluctuations and non-Gaussian stochasticity. In spintronic devices, thermally activated N\'eel switching creates heavy-tailed noise that masks weak signals, defeating linear filters optimized for Gaussian statistics. Here, we introduce a physics-integrated inference framework that decouples signal morphology from stochastic transients using a hierarchical 1D CNN-GRU topology. By learning the temporal signatures of N\'eel relaxation, this architecture reduces the Noise Equivalent Differential Temperature (NEDT) of spintronic Poisson bolometers by a factor of six (233.78 mK to 40.44 mK), effectively elevating room-temperature sensitivity toward cryogenic limits. We demonstrate the framework's universality across the electromagnetic and biological spectrum, achieving a 9-fold error suppression in Radar tracking, a 40\% uncertainty reduction in LiDAR, and a 15.56 dB SNR enhancement in ECG. This hardware-inference coupling recovers deterministic signals from fluctuation-dominated regimes, enabling near-ideal detection limits in noisy edge environments.

physics.optics↗

arXiv2026

Uncooled Poisson Bolometer for High-Speed Event-Based Long-wave Thermal Imaging

Event-based vision provides high-speed, energy-efficient sensing for applications such as autonomous navigation and motion tracking. However, implementing this technology in the long-wave infrared remains a significant challenge. Traditional infrared sensors are hindered by slow thermal response times or the heavy power requirements of cryogenic cooling. Here, we introduce the first event-based infrared detector operating in a Poisson-counting regime. This is realized with a spintronic Poisson bolometer capable of broadband detection from 0.8-14$\mu\text{m}$. In this regime, infrared signals are detected through statistically resolvable changes in stochastic switching events. This approach enables room-temperature operation with high timing resolution. Our device achieves a maximum event rate of 1,250 Hz, surpassing the temporal resolution of conventional uncooled microbolometers by a factor of 4. Power consumption is kept low at 0.2$\mu$W per pixel. This work establishes an operating principle for infrared sensing and demonstrates a pathway toward high-speed, energy-efficient, event-driven thermal imaging.

physics.optics↗

arXiv2026

Ultra-broadband Mid to Long-wave Infrared Spintronic Poisson Bolometer

Infrared detectors have traditionally been divided into two fundamental classes, mid-wave (MWIR, 3-5 um) and long-wave (LWIR, 8-14 um). Integrating MWIR and LWIR within a single device is challenging due to distinct materials, cooling needs, and detection mechanisms, while such integration is critical for improved object recognition, temperature estimation, and environmental sensing. In this work, we demonstrate a Spintronic Poisson (SP) bolometer enabling room-temperature ultra-broadband sensing across 3-14 um. Unlike conventional bolometers that rely on continuous analog signals, the SP bolometer implements a Poisson-counting detection paradigm, encoding temperature in discrete stochastic events, which turns thermal noise from a limitation into the basis of the estimator itself. We fabricate the SP bolometer using a spintronic transduction layer integrated with a plasmonic nanoantenna array to enhance broadband infrared absorption. Using spintronic transduction, the device achieves the noise-equivalent temperature difference (NETD, thermal sensitivity metric) of 80-100 mK at 300 K, surpassing uncooled detectors and approaching cooled technologies. This work establishes a statistical detection paradigm for room-temperature infrared sensing with broad application potential.

physics.optics↗

arXiv2025

Optical Response in Spintronic Poisson Bolometers

Analog bolometers based on temperature-dependent phase-transition materials such as vanadium oxide (VOx) and barium titanate (BTO) represent the state of the art in uncooled infrared detectors. Recently, the first room-temperature spintronic Poisson bolometer based on magnetic tunnel junctions (MTJs) was proposed and demonstrated as a promising infrared detector. Unlike conventional bolometers, the spintronic Poisson bolometer operates in a probabilistic regime dominated by Poissonian noise, where the response is governed by resistance fluctuations arising from thermally activated magnetization transitions. Spontaneous transitions between two metastable magnetic states occur even in the absence of incident light, and the transition probability increases under illumination. In this work, we experimentally study the statistical properties of the optical response of the spintronic Poisson bolometer under illumination. We demonstrate that transitions in spintronic Poisson bolometers, both in the absence and presence of light, exhibit Poissonian behavior, with transition rates and interarrival times modulated by incident radiation. Under illumination, we observe a 153% increase in the count rate accompanied by a 70% reduction in interarrival time. These results establish spintronic Poisson bolometers as a promising platform for probabilistic, high-speed, and high-sensitivity infrared detection at room temperature.

physics.optics↗

arXiv2025

Poisson wavefront imaging in photon-starved scenarios

Low-photon phase imaging is essential in applications where the signal is limited by short exposure times, faint targets, or the need to protect delicate samples. We address this challenge with Poisson Wavefront Imaging (PWI), an optimization-based method that incorporates Poisson photon statistics and a smoothness prior to improve wavefront reconstruction. By using multiple spatial light modulator's phase patterns, PWI enhances Fisher information, boosting theoretical accuracy and regularizing the retrieval process effectively. In simulations, PWI approaches the theoretical phase error limit, and in experiments it reduces phase error by up to 1.6x compared to the Gerchberg-Saxton algorithm, achieving 1.8x higher resolution wavefront imaging in low photon regime. This method advances photon-limited imaging with applications in astronomy, semiconductor metrology, and biological systems.

physics.optics↗

arXiv2025

Enhanced Sensitivity to Blackbody Radiation in Spintronic Poisson Bolometers

High-sensitivity long-wave infrared (LWIR) detection is crucial for observing weak thermal radiation. Recently, the Poisson bolometer has been proposed as a fundamentally new platform for uncooled infrared detection. In contrast to traditional analog detectors, where signal and noise are determined by continuous currents or voltages, the Poisson bolometer's signal and noise are governed by Poissonian counting statistics regardless of the light source. In this work, we demonstrate advancements in uncooled infrared detection towards cryogenic-level sensitivity through the integration of spintronic and plasmonic materials. Specifically, a spintronic Poisson bolometer is experimentally integrated with a plasmonic nanoantenna array optimized for broadband LWIR absorption to enhance the temperature increase of the sensing layer. The plasmonic absorber exhibits an absorptance exceeding 60\% across the LWIR spectrum, matching the peak of room-temperature blackbody radiation. We demonstrate that these devices are capable of achieving a noise equivalent differential temperature (NEDT) of 35 mK at a 50 Hz frame rate, demonstrating room-temperature performance comparable to the most sensitive uncooled LWIR detectors reported to date. This work opens up a pathway to removing bulky and expensive cooling requirements from high-sensitivity LWIR detection and imaging applications, such as remote sensing, high-speed imaging, and industrial monitoring.

physics.optics↗

arXiv2025

Design of Microlens Arrays for Thermal Imaging with Spintronic Poisson Bolometers

Infrared (IR) detectors are widely used due to their ability to sense thermal radiation. Recently, a room-temperature infrared detector known as the spintronic Poisson bolometer was introduced. While offering fast digital readout, its sensitivity is currently limited by its small photosensitive area and array fill factor. Beyond this specific detector, many emerging detector architectures also require substantial in-pixel electronics or engineering tradeoffs, which can reduce the fill factor and degrade optical coupling efficiency. In this work, we present design guidelines for spherical plano-convex microlens arrays that enhance light collection in spintronic Poisson bolometer arrays in the mid-wave infrared (MWIR). Guided by the simulations, we fabricate a microlens array sample to demonstrate that the chosen geometrical parameters are experimentally attainable and compatible with the fabrication process. We then systematically explore the scaling laws between sensor active size, microlens geometries, and the resulting light collection metrics, yielding practical design rules that are broadly relevant to MWIR detector arrays with limited active area. A radiometric-stochastic model is used to quantify the resulting sensitivity improvements for the spintronic Poisson bolometer. Our work is the first systematic simulation of a microlens design with spintronic Poisson bolometer arrays, bridging microphotonics, spintronics, and thermal imaging.

physics.optics↗

arXiv2025

Photon-starved imaging through turbulence at the diffraction limit

Ground-based imaging systems struggle to achieve diffraction-limited resolution when atmospheric turbulence and photon scarcity act simultaneously. In this regime, conventional adaptive optics, speckle imaging, and blind deconvolution lack sufficient information diversity to reliably estimate either the scene or the turbulence. We present Turbulence Aware Poisson Blind Deconvolution (TAP-BD), a framework designed for robust image recovery in these extreme conditions. TAP-BD extracts more information from coded-detection through phase diversity and decodes it with a physics-informed optimization that incorporates low photon Poisson statistics. Experiments show that TAP-BD provides reliable reconstructions of both scene and turbulence using only a few tens of measurements, even under strong aberrations and photon-starved conditions where existing methods fail. This capability enables photon-efficient, turbulence resilient imaging for applications such as space situational awareness and long-range remote sensing.

physics.optics↗

arXiv2025

Long wave infrared detection using probabilistic spintronic bolometer arrays

The use of probabilistic spintronic devices for infrared radiation detection has introduced a shift in approach to thermal imaging. The integration of probabilistic magnetic tunnel junctions with infrared plasmonic nano-antennas achieves high-sensitivity digital-mode infrared sensors at room temperature. Here, we present a scalable approach towards multipixel plasmonic-spintronic bolometer array fabrication and readout. We fabricate proof-of-concept 2x2 row-column multiplexed probabilistic plasmonic sprintronic arrays and show their response to long-wave infrared radiation (8-14um) with high readout speeds (10K-1M counts per second). These spintronic, ultrafast, nanoscale (SUN) bolometers can result in novel high-pixel density CMOS compatible infrared detection platforms. Our work provides a broadband (9kHz to 3GHz) readout platform for future digital probabilistic detector applications. Furthermore, our approach addresses a key challenge associated with scaling infrared pixel sizes that can drive progress towards high pixel density detector arrays for infrared sensing and microscopy applications.

physics.ins-det↗

arXiv2025

Unified Theory of Dark Count Rate and System Detection Efficiency for NbN, WSi Based Superconducting Single Photon Detectors

Predicting the behavior of superconducting nanowire single photon detectors (SNSPDs) is important as their use becomes more widespread in fields ranging from quantum computing to quantum remote sensing. Here, we present a vortex crossing theory of photon detection which provides a unified definition of system detection efficiency and dark count rates. Our approach quantitatively captures the plateau region of system detection efficiency for NbN and WSi based SNSPDs. We concurrently predict the temperature dependence of dark count rates and the intrinsic timing jitter of SNSPDs. We extensively benchmark our model against various experiments to aid in the design of the next generation of SNSPDs.

cond-mat.supr-con↗

arXiv2025

Type-1.5 SNSPD: Interacting vortex theory of two bandgap superconducting single photon detectors

Photon detectors based on type-2 superconductors have found widespread applications from on-chip quantum computing to quantum remote sensing. Here, we develop the theory for a new class of type-1.5 superconducting nanowire single photon detectors (SNSPDs) based on two bandgap superconductors with high transition temperatures such as MgB2 (Tc ~38.6K). We show that vortex-vortex interactions in two component condensates lead to a unique operating regime where single photons can seed multiple vortices within a hotspot. We also show that dark counts are suppressed in the type-1.5 regime compared to the widely studied type-2 SNSPDs. Our work opens the door for exploring the unique vortex physics of two-gap superconductors for quantum device applications.

cond-mat.supr-con↗

arXiv2022

Optically induced static magnetic field in ensemble of nitrogen-vacancy centers in diamond

Generation of local magnetic field at the nanoscale is desired for many applications such as spin-qubit-based quantum memories. However, this is a challenge due to the slow decay of static magnetic fields. Here, we demonstrate photonic spin density (PSD) induced effective static magnetic field for an ensemble of nitrogen-vacancy (NV) centers in bulk diamond. This locally induced magnetic field is a result of coherent interaction between the optical excitation and the NV centers. We demonstrate an optically induced spin rotation on the Bloch sphere exceeding 10 degrees which has potential applications in all optical coherent control of spin qubits.

quant-ph↗

arXiv2021

Quantum sensing of photonic spin density

Photonic spin density (PSD) in the near-field gives rise to exotic phenomena such as photonic skyrmions, optical spin-momentum locking and unidirectional topological edge waves. Experimental investigation of these phenomena requires a nanoscale probe that directly interacts with PSD. Here, we propose and demonstrate that the nitrogen-vacancy (NV) center in diamond can be used as a quantum sensor for detecting the spinning nature of photons. This room temperature magnetometer can measure the local polarization of light in ultra-subwavelength volumes through photon-spin-induced virtual transitions. The direct detection of light's spin density at the nanoscale using NV centers in diamond opens a new frontier for studying exotic phases of photons as well as future on-chip applications in spin quantum electrodynamics (sQED).

quant-ph↗