Quantum Imagery Applications In The Future
Abstract
Quantum imagery is a diverse topic of study that offers ultralow-light microscopy and very efficient imaging in extreme spectrum bands. The field has progressed from extremely exciting academic study to the edge of demonstrating tangible technological advancements in imaging and microscopy since the first proof-of-concept tests over 30 years ago. The goal of this paper is to provide researchers outside of the quantum optical community, particularly those working with imaging technology, with an overview of several promising quantum imagery approaches, as well as to assess both the quantum benefit and the prospects for practical application in the near future. Several use case scenarios are covered, as well as a thorough examination of related technology needs and required advances in order to achieve practical and commercial implementation.
Introduction
Optical microscopy and spectroscopy are important techniques in current study spanning a wide range of disciplines, from fundamental physics to material science, chemistry, and biology. It's fascinating to see how increasing understanding of light's nature has led to new imaging applications throughout history. The simplest way to describe light is to think of it as ray bundles ("Strahlenbündel"). This geometric optics illustration allows the working principle of lenses to be described, as well as its application in the form of magnification glasses, for example. However, understanding diffraction and interference requires taking into consideration the wave form of light. This is used in interference microscopes, for example. The resolution of an optical system is linearly proportional to the wavelength of the light utilized for observation, which is inextricably tied to this knowledge. At the turn of the twentieth century, the fundamental revelation that light is made up of discrete energy components called quanta sparked the so-called first quantum revolution. It serves as the foundation for the entire photonics and laser sector. Furthermore, fluorescence microscopy, a flexible and widely used technique in modern life science, cannot be described without this discovery. We are currently witnessing the second quantum revolution, in which quantum states capable of superposition and entanglement are being exploited for quantum technology applications. Various novel imaging methods are now possible thanks to these new findings.
Many researchers all around the world are working to overcome the limits of today's recognized imaging systems. Resolution, SNR, contrast, and spectral range are all addressed. One method to get around some of these constraints is to use light's quantum qualities. Entanglement plays a key part in this process. Momentum, energy, and position correlations of entangled photon pairs are particularly important. They enable spectroscopy and imaging in spectral bands where efficient detection is impossible, as well as imaging with light that has never come into contact with a material. Additionally, by employing specific quantum states of light and their photon number statistics, sensing and imaging beyond classical restrictions, such as the shot noise level, is conceivable. Additionally, when using quantum light, two-photon fluorescence microscopy can be performed at extremely low light intensities, allowing for new insights into photosensitive biological probes.
Many quantum-enhanced imaging systems, in essence, take advantage of the advantageous features of correlated photon pairs. We'd want to have a look at some of the different photon-based imaging approaches. First, we go over the fundamental properties of many quantum states of light and highlight the unique properties of photon pairs and associated states. We also go over how photon pairs are usually formed and how their attributes are related to the process. Photon pairs can be used in a variety of ways for imaging, with the photons being used in fundamentally different ways. The number of photons that interact with the object and are used to record an image is how we structure our review of imaging technologies. Quantum imaging approaches use only one of the pair's photons to interact with the sample, while the other is used to make the measurements. The image generation is based on quantum interference of many sources in this case. In contrast, whereas only one photon of the pair interacts with the sample in the procedures discussed in Section 4, both are required to construct an image based on their intrinsic correlations. Finally, techniques in which the entire pair interacts with the item and is detected or produces fluorescence light that can be detected. Entanglement of photon pairs is used in these methods. Standard microscopy techniques such as phase contrast microscopy and laser scanning microscopy can be directly compared.
Some of the imaging techniques mentioned here are based on spatial correlations between the two photons in a pair that are created during the generation process. Due to the presence of analogous correlations in the spectrum of photon pairs, equivalent quantum-enhanced spectroscopy methods have been developed, which will also be discussed here.
Basically, all of the methods presented so far have only been examined in principle and have yet to be implemented in real-world applications. As a result, in our discussion, we will emphasize their specific advantages as well as possible applications where these advantages would be useful. In addition, significant experimental problems that must be overcome in order to promote the applicability of the stated approaches will be discussed. These are frequently linked to the quantum light source's or detecting hardware's features. To assess the state of the art in these disciplines in terms of the obstacles associated with adopting quantum imaging techniques.
We'd also like to call attention to a few review papers and overview pieces that address issues that are mentioned here but are outside the scope of this review: single photon generators and detectors,15-17 integrated-optical sources of entangled photons,18, 19 and spontaneous four-wave mixing creation of photon pairs
Fundamentals
When you consider the quantum nature of light, you may imagine new imaging schemes that could be implemented in quantum-enhanced microscopes or imaging devices. The non-classical features or processes connected with quantum light that immediately give rise to applications in the field of quantum-enhanced imaging are briefly explained in this article.
Quantum Imagery Based On Correlation
The imaging and spectroscopy systems detailed so far were based on detecting only one photon of the pair generated by SPDC, with the second photon serving to mediate interference between the many probable photon pairs' origins. This section will cover imaging systems in which only one photon interacts with the material yet both are observed. The spatial correlation between the two photons in a pair is responsible for the generation of the observed image in this case.
Quantum Ghost Detection
Quantum ghost imaging is the most well-known of these imaging techniques (QGI). The two photons of an SPDC-generated correlated photon pair are divided into two independent beams here. One of these beams, such as the signal, is utilized to illuminate the item, and the photons transmitted by the signal are then detected using a bucket detector. The idler beam, on the other hand, is distinguished by a spatially resolving single-photon detector that can be implemented using either an array or a single scanning detector. Both detectors cannot generate an image of the object on their own since one does not get spatial information and the other does not receive object information. The image, however, is visible in the correlation signal of the two observations. This imaging approach takes advantage of the fact that a pair's photons are always fully linked in time and, ideally, in space. As a result, measuring the position of the idler photon with the spatially resolving detector is sufficient to establish the position of the signal photon on the object, while monitoring the transmitted photon statistics will eventually lead to an estimate of the object transmission at that place.