In the domain of light emissions, quantum mechanics has been an immensely successful guiding tool for us. In the propagation of light and optical instrument design, Huygens-Fresnel diffraction integral (HFDI) (or its advanced versions) and Maxwell’s wave equation are continuing to be the essential guiding tools for optical scientists and engineers. In fact, most branches of optical science and engineering, like optical instrument design, image processing, Fourier optics, Holography, etc., cannot exist without using the foundational postulates behind the Huygens-Fresnel diffraction integral. Further, the field of structured light is also growing where phases and the state of polarizations are manipulated usually with suitable classical macro-devices to create wave fronts that restructured through light-matter interactions through these devices. Mathematical modeling of generating such complex wave fronts generally follows classical concepts and classical macro tools of physical optics. Some of these complex light beams can impart mechanical angular momentum and spin-like properties to material particles inserted inside these structured beams because of their electromagnetic dipolar properties and/or structural anisotropy. Does that mean these newly structured beams have acquired new quantum properties without being generated through quantum devices and quantum transitions? In this chapter, we bridge the classical and quantum formalism by defining a hybrid photon (HP). HP is a quantum of energy, hν, at the initial moment of emission. It then immediately evolves into a classical time-finite wave packet, still transporting the original energy, hν, with a classical carrier frequency ν (oscillation of the E-vector). This chapter will raise enquiring questions whether all these observed “quantum-like” behaviors are manifestations of the joint properties of interacting material particles with classical EM waves or are causal implications of the existence of propagation of “indivisible light quanta” with exotic properties like spin, angular momentum, etc.
In the domain of light emissions, quantum mechanics has been an immensely successful guiding tool for us. In the propagation of light and optical instrument design, Huygens-Fresnel diffraction integral (HFDI) (or its advanced versions) and Maxwell’s wave equation are continuing to be the essential guiding tools for optical scientists and engineers. In fact, most branches of optical science and engineering, like optical instrument design, image processing, Fourier optics, Holography, etc., cannot exist without using the foundational postulates behind the Huygens-Fresnel diffraction integral. Further, the field of structured light is also growing where phases and the state of polarizations are manipulated usually with suitable classical macro-devices to create wave fronts that restructured through light-matter interactions through these devices. Mathematical modeling of generating such complex wave fronts generally follows classical concepts and classical macro tools of physical optics. Some of these complex light beams can impart mechanical angular momentum and spin-like properties to material particles inserted inside these structured beams because of their electromagnetic dipolar properties and/or structural anisotropy. Does that mean these newly structured beams have acquired new quantum properties without being generated through quantum devices and quantum transitions? In this chapter, we bridge the classical and quantum formalism by defining a hybrid photon (HP). HP is a quantum of energy, hν, at the initial moment of emission. It then immediately evolves into a classical time-finite wave packet, still transporting the original energy, hν, with a classical carrier frequency ν (oscillation of the E-vector). This chapter will raise enquiring questions whether all these observed “quantum-like” behaviors are manifestations of the joint properties of interacting material particles with classical EM waves or are causal implications of the existence of propagation of “indivisible light quanta” with exotic properties like spin, angular momentum, etc.
We present observational and causality arguments to underscore that a better model for light is a “hybrid photon” wave packet. At the moment of quantum transitions, the electromagnetic energy is embedded in the transient quantum, hν. But, it immediately evolves into a diffractively spreading classical, quasi-exponential, EM wave packet. This hybrid photon accommodates both quantum and classical optics. The quantum formalism has demonstrated staggering successes in modeling the micro world of atoms. The Huygens-Fresnel diffraction integral and Maxwell’s wave equation are also enjoying continued successes since early 1800’s. In this paper, using the model of hybrid photon, we underscore that the photoelectron counting statistics should vary depending upon the relative phases, spacing and amplitudes of the superposed wave packets (hybrid photons) as they simultaneously arrive and stimulate the quantum mechanical dipole complexes on the surface of the photo detectors.
Einstein’s 1905 paper on the photoelectric effect successfully modeled the published data while explicitly defining light as “indivisible light quanta”. One of the key successes of Quantum Mechanics (QM) of 1925-26, is the release of discrete packet of energy hv during any quantum level transitions in atoms and molecules. These two modern successes have overturned the mathematical and experimental knowledge developed over several centuries behind the optical science and engineering, without successfully bridging the knowledge gap epitomized by the still unresolved “wave-particle-duality” (WPD). Note that, optical science and engineering fields are still thriving using Huygens-Fresnel diffraction integral (HF-DI) of 1817 and Maxwell’s wave equations of 1876, without any controversy. This chapter resolves this dichotomy by eliminating the need for WPD. We provide a model for the atomic emission as a discrete packet of energy hv, as required by QM, but which evolves and propagates out as a Maxwellian classical exponential wave packet, while diffractively spreading out obeying the HF-DI. The continuing need to accept the magical WPD arises because we have not been systematically and explicitly exploring the two-step physical processes which take place during light-detector interaction before the photoelectric data is generated by our apparatus. The two steps are: (i) Linear amplitude-amplitude stimulation induced on the detecting dipoles by the light wave vector; (ii) which is then followed by the quadratic energy absorption step by the detector. If the detector is an LCR oscillator (for radio waves), or an old fashioned Bolometer (for higher frequencies), we would not observe any quantumness in the data. But, when we use a modern quantum photodetector using higher frequency EM waves, we can count highly amplified current pulses of electrons, generated out of each one of the released electron, bound quantum mechanically inside the detector.
Sensors are measuring tools. In any measurement, we have at least two different kinds of interactants. We never know all there are to know about any one of these interactants and the interaction processes that are mostly invisible. Yet, our engineering innovation driven evolution is persisting for over five million years. It is then important to articulate explicitly our Interaction Process Mapping Thinking (IPM-T) that we keep applying in the real world without formally recognizing it. We present how the systematic application of IPM-T removes century old wave-particle duality by introducing a model of hybrid photon. It seamlessly bridges the quantum and the classical worlds. Photons are discrete energy packets only at the moment of emission; then they evolve diffractively and propagate as classical waves. Thus, "interference of a single indivisible photon" is only a non-causal assertion. We apply IPM-T to improve the photoelectric equation and we obtain Non-Interaction of Wave (NIW) amplitudes. Note that Huygens explicitly articulated NIW by postulating his "secondary spherical wavelets." Later Fresnel incorporated this postulate in the now famous Huygens- Fresnel (HF) diffraction integral. Most modern optical science and engineering are based upon propagating EM waves through optical devices and systems using this integral in some form or other. Maxwell’s wave equation accepts HF integral as its solution. Systematic application of IPM-T to our causal and working mathematical equations, along with NIW in interferometric experiments, reveal that Superposition Effects can emerge only when the interacting material dipoles respond, whether classically or quantum mechanically, to the joint stimulations due to all the simultaneously superposed waves. This indicates the non-causality of our belief that a single indivisible photon can interfere by itself. We would not have a causally evolving universe had any stable elementary particle were to change itself through selfinterference. Further, our working superposition equations always contain two or more terms representing two or more independently evolving entities. That is why we need physical instruments with two or more independent channels of propagation along with appropriately placed detectors to generate physical superposition effects. Nature does not violate causality. Otherwise, our causally framed equations would not have been working so elegantly.
Recent progress in meta-optics, particularly the development of metasurfaces, has enabled compact, tunable, and integrable control over the amplitude, phase, polarization, and wavefront of light, thereby allowing a paradigm shift in traditional optical science and engineering. In parallel, the ability to generate and precisely manipulate nonclassical light is central to quantum optics, enabling key functionalities in secure quantum communication, precision measurement, and scalable quantum computation. This review aims to bridge these two rapidly advancing fields by presenting recent progress in the application of structured materials to the manipulation of quantum states of light. We begin by introducing the concept of singular optics, followed by a discussion of various families of spatially and temporally structured beams that form the foundation for many of the phenomena explored in quantum photonics. Next, we revisit the theoretical framework of quantum optics, including the formalism of photon quantization and the principles governing quantum frequency conversion. We then examine how metasurfaces can be engineered to enable highly efficient nonlinear quantum processes, including both up-conversion and down-conversion, thereby offering new approaches for generating and controlling complex quantum states. Furthermore, we discuss the crucial role of structured materials in shaping the properties of quantum light and in applications such as quantum ghost imaging. The review concludes by identifying emerging directions for integrating meta-optical platforms with quantum systems, highlighting their potential for scalable manipulation of nonclassical light at the nanoscale.
Our starting platform is the staggering and pervasive successes of the Huygens-Fresnel principle (HFP) from macro to nano photonics fields, which model the propagation as if each point on the wave front serves as a secondary point source. Summation of the complex amplitudes of these secondary wave fronts with proper inclination factor gives us remarkably accurate results for every possible realistic situation. Therefore, we take the concept of secondary point source of "energy" as a reality in all of cosmic space, irrespective of whether the space is "empty" or filled with "materials" as we understand them. It amounts to accepting the existence of an all pervading cosmic tension field (CTF). We justify our platform by comparing and contrasting with the various "material" based propagating waves that we can generate and experience, which always require the existence of uniform tension field energy at every point. Then we show that two of the key motivations behind Dirac's quantization of the EM field can easily be accommodated by semi-classical model a la Jaynes (quantized atoms and classical EM wave packet). They are: (i) Photo electric effects that require photon to be indivisible packets of energy; and (ii) QM transition rule requiring the emission of a unique frequency ν would violate "monochromaticity" rule implied by Fourier's time-frequency theorem and "coherence theory" if photons were to be time-finite classical wave packets.