Roknuzzaman, Md, Sathwik Bharadwaj, Yifan Wang, Chinmay Khandekar, Dan Jiao, Rajib Rahman, and Zubin Jacob. (2023) 2023. “First-principles study of large gyrotropy in MnBi for infrared thermal photonics”. Physical Review B 108 (22).

Nonreciprocal gyrotropic materials have attracted significant interest recently in material physics, nanophotonics, and topological physics. Most of the well-known nonreciprocal materials, however, only show nonreciprocity under a strong external magnetic field and within a small segment of the electromagnetic spectrum. Here, through first-principles density-functional theory calculations, we show that due to strong spin-orbit coupling manganese-bismuth (MnBi) exhibits nonreciprocity without any external magnetic field and a large gyrotropy in a broadband long-wavelength infrared regime. Further, we design a multilayer structure based on MnBi to obtain a maximum degree of spin-polarized thermal emission at 7 µm. The connection established here between large gyrotropy and the spin-polarized thermal emission points to the potential use of MnBi to develop spin-controlled thermal photonics platforms.

Lobet, Michaël, Nathaniel Kinsey, Iñigo Liberal, Humeyra Caglayan, Paloma A. Huidobro, Emanuele Galiffi, Jorge Ricardo Mejía-Salazar, Giovanna Palermo, Zubin Jacob, and Nicolò Maccaferri. (2023) 2023. “New Horizons in Near-Zero Refractive Index Photonics and Hyperbolic Metamaterials”. ACS Publications.

The engineering of the spatial and temporal properties of both the electric permittivity and the refractive index of materials is at the core of photonics. When vanishing to zero, those two variables provide efficient knobs to control light–matter interactions. This Perspective aims at providing an overview of the state of the art and the challenges in emerging research areas where the use of near-zero refractive index and hyperbolic metamaterials is pivotal, in particular, light and thermal emission, nonlinear optics, sensing applications, and time-varying photonics.

Bao, Fanglin, Xueji Wang, Shree Hari Sureshbabu, Gautam Sreekumar, LIPING YANG, Vaneet Aggarwal, Vishnu N. Boddeti, and Zubin Jacob. (2023) 2023. “Heat-assisted Detection and Ranging”. Nature 619: 743–748 .

Machine perception uses advanced sensors to collect information about the surrounding scene for situational awareness. State-of-the-art machine perception using active sonar, radar and LiDAR to enhance camera vision faces difficulties when the number of intelligent agents scales up. Exploiting omnipresent heat signal could be a new frontier for scalable perception.

However, objects and their environment constantly emit and scatter thermal radiation, leading to textureless images famously known as the ‘ghosting effect’. Thermal vision thus has no specificity limited by information loss, whereas thermal ranging—crucial for navigation—has been elusive even when combined with artificial intelligence (AI).

Here we propose and experimentally demonstrate heat-assisted detection and ranging (HADAR) overcoming this open challenge of ghosting and benchmark it against AI-enhanced thermal sensing. HADAR not only sees texture and depth through the darkness as if it were day but also perceives decluttered physical attributes beyond RGB or thermal vision, paving the way to fully passive and physics-aware machine perception.

We develop HADAR estimation theory and address its photonic shot-noise limits depicting information-theoretic bounds to HADAR-based AI performance. HADAR ranging at night beats thermal ranging and shows an accuracy comparable with RGB stereovision in daylight. Our automated HADAR thermography reaches the Cramér–Rao bound on temperature accuracy, beating existing thermography techniques.

Our work leads to a disruptive technology that can accelerate the Fourth Industrial Revolution (Industry 4.0) with HADAR-based autonomous navigation and human–robot social interactions.

Sun, Wenbo, Sathwik Bharadwaj, Li-Ping Yang, Yu-Ling Hsueh, Yifan Wang, Dan Jiao, Rajib Rahman, and Zubin Jacob. 2023. “Limits to Quantum Gate Fidelity from Near-Field Thermal and Vacuum Fluctuations”. Physical Review Applied 19.

High-fidelity quantum gate operations are essential for achieving scalable quantum circuits. In spin qubit quantum computing systems, metallic gates and antennas that are necessary for qubit operation, initialization, and readout, also cause detrimental effects by enhancing fluctuations of electromagnetic fields. Therefore, evanescent wave Johnson noise (EWJN) caused by near-field thermal and vacuum fluctuations becomes an important unmitigated noise, which induces the decoherence of spin qubits and limits the quantum gate operation fidelity. Here, we first develop a macroscopic quantum electrodynamics theory of EWJN to account for the dynamics of two spin qubits interacting with metallic circuitry. Then we propose a numerical technique based on volume integral equations to quantify EWJN strength in the vicinity of nanofabricated metallic gates with arbitrary geometry. We study the limits to two-spin-qubit gate fidelity from EWJN-induced relaxation processes in two experimentally relevant quantum computing platforms: (a) the silicon quantum dot system and (b) nitrogen-vacancy centers in diamond. Finally, we introduce a Lindbladian engineering method to optimize the control pulse sequence design and show its enhanced performance over Hamiltonian engineering in mitigating the influence of thermal and vacuum fluctuations. Our work leverages advances in computational electromagnetics, fluctuational electrodynamics, and open quantum systems to suppress the effects of near-field thermal and vacuum fluctuations and reach the limits of two-spin-qubit gate fidelity.

Wang, Xueji, Tyler Sentz, Sathwik Bharadwaj, Subir Kumar Ray, Yifan Wang, Dan Jiao, Limei Qi, and Zubin Jacob. (2023) 2023. “Observation of nonvanishing optical helicity in thermal radiation from symmetry-broken metasurfaces”. Science Advances 9 (4).

Spinning thermal radiation is a unique phenomenon observed in condensed astronomical objects, including the Wolf-Rayet star EZ-CMa and the red degenerate star G99-47, due to the existence of strong magnetic fields. Here, by designing symmetry-broken metasurfaces, we demonstrate that spinning thermal radiation with a nonvanishing optical helicity can be realized even without applying a magnetic field. We design nonvanishing optical helicity by engineering a dispersionless band that emits omnidirectional spinning thermal radiation, where our design reaches 39% of the fundamental limit. Our results firmly suggest that metasurfaces can impart spin coherence in the incoherent radiation excited by thermal fluctuations. The symmetry-based design strategy also provides a general pathway for controlling thermal radiation in its temporal and spin coherence.

López, Adrian E. Rubio, Ashwin K. Boddeti, Fanglin Bao, Hyunsoo Choi, and Zubin Jacob. (2023) 2023. “Nonequilibrium Hanbury Brown-Twiss interferometry: Theory and application to binary stars”. Physical Review Research 5 (013057 ).

Intensity interferometry based on Hanbury Brown and Twiss’s seminal experiment for determining the radius of the star Sirius formed the basis for developing the quantum theory of light. To date, the principle of this experiment is used in various forms across different fields of quantum optics, imaging, and astronomy. Although the technique is powerful, it has not been generalized for objects at different temperatures. Here, we address this problem using a generating functional formalism by employing the P-function representation of quantum-thermal light. Specifically, we investigate the photon coincidences of a system of two extended objects at different temperatures using this theoretical framework. We show two unique aspects in the second-order quantum coherence function: interference oscillations and a long-baseline asymptotic value that depends on the observation frequency, temperatures, and size of both objects. We apply our approach to the case of binary stars and discuss the advantages of measuring these two features in an experiment. In addition to the estimation of the radii of each star and the distance between them, we also show that the present approach is suitable for the estimation of temperatures as well. To this end, we apply it to the practical case of binary stars Luhman 16 and Spica α Vir. We find that for currently available telescopes, an experimental demonstration is feasible in the near term. Our work contributes to the fundamental understanding of intensity interferometry of quantum-thermal light and can be used as a tool for studying two-body thermal emitters, from binary stars to extended objects.

Wang, Xueji, Ziyi Yang, Fanglin Bao, Tyler Sentz, and Zubin Jacob. (2023) 2023. “Spinning Meta-Cam: Spectro-Polarimetric Long-wave Infrared Thermal Imaging based on Spinning Metasurfaces”. ArXiv.

Spectro-polarimetric imaging in the long-wave infrared (LWIR) region is a powerful tool for capturing temperature, material composition, and surface morphology information. However, current spectro-polarimetric LWIR imagers are often bulky and severely limited in spectral resolution and field of view (FOV). In this work, we present a new paradigm for spectro-polarimetric demultiplexing by combining large-area meta-optical devices and advanced computational imaging algorithms. We use the intrinsic dispersion and polarization modulation of anisotropic spinning metasurfaces to achieve simultaneous spectral and polarimetric resolution without the need for bulky filter wheels or interferometers. Our spinning-metasurface-based spectro-polarimetric module is robust, compact (< 10 x 10 x 10 cm), and has a wide field of view (25◦ ). Our approach represents a significant advancement in the field of thermal imaging, allowing for high-quality, information-rich thermal image data for a wide range of applications such as astronomical exploration, medical diagnosis, and agricultural monitoring.


Javidian, Mohammad Ali, Vaneet Aggarwal, and Zubin Jacob. 2022. “Quantum Causal Inference in the Presence of Hidden Common Causes: an Entropic Approach”. Physical Review Applied 106 (062425).

Quantum causality is an emerging field of study that has the potential to greatly advance our understanding of quantum systems. In this paper, we put forth a theoretical framework for merging quantum information science and causal inference by exploiting entropic principles. For this purpose, we leverage the tradeoff between the entropy of hidden cause and the conditional mutual information of observed variables to develop a scalable algorithmic approach for inferring causality in the presence of latent confounders (common causes) in quantum systems. As an application, we consider a system of three entangled qubits and transmit the second and third qubits over separate noisy quantum channels. In this model, we validate that the first qubit is a latent confounder and the common cause of the second and third qubits. In contrast, when two entangled qubits are prepared and one of them is sent over a noisy channel, there is no common confounder. We also demonstrate that the proposed approach outperforms the results of classical causal inference for the Tubingen database when the variables are classical by exploiting quantum dependence between variables through density matrices rather than joint probability distributions. Thus, the proposed approach unifies classical and quantum causal inference in a principled way.

Wang, Xueji, and Zubin Jacob. (2022) 2022. “Symmetry Breaking In Thermal Photonics”. Light: Science & Applications.

Engineering symmetries in nanostructures and metasurfaces provides a new paradigm to control incoherent heat radiation for applications in energy conversion, thermal sources, infrared imaging, and radiative cooling.

Bharadwaj, Sathwik, Todd Van Mechelen, and Zubin Jacob. 2022. “Picophotonics: Anomalous Atomistic Waves in Silicon”. Physical Review Applied 18 (4).

The concept of photonic frequency-momentum (ω-q) dispersion has been extensively studied in artificial dielectric structures such as photonic crystals and metamaterials. However, the ω-q dispersion of electrodynamic waves hosted in natural materials at the atomistic level is far less explored. Here, we develop a Maxwell Hamiltonian theory of matter combined with the quantum theory of atomistic polarization to obtain the electrodynamic dispersion of natural materials interacting with the photon field. We apply this theory to silicon and discover the existence of anomalous atomistic waves. These waves occur in the spectral region where propagating waves are conventionally forbidden in a macroscopic theory. Our findings demonstrate that natural media can host a variety of yet to be discovered waves with subnanometer effective wavelengths in the picophotonics regime.