Designing and controlling quantum cascade lasers for quantum technologies: towards a new generation of infrared sub-classical sources
Francesco Cappelli, Simone Borri, Luigi Consolino, Tecla Gabbrielli, Alessia Sorgi, G. Roati, Francesco Scazza, Andrea Trombettoni, M. Giuntini, Alessio Montori, Mario Siciliani de Cumis, Natalia Bruno, Augusto Smerzi, Alessandro Zavatta, M. De Rosa, Iolanda Ricciardi, Paolo De Natale
Laser sources, since their invention, have proved to be the right solution in practically all conceived applications. Recently, the so-called second quantum revolution and quantum technologies like sensing, computing, simulation or communication are triggering a new generation of sub-classical sources to tackle such novel and challenging applications. First concepts and experimental results aimed to endow quantum cascade lasers and other infrared sources with truly quantum properties will be shown.
Laser sources, since their invention, have proved to be the right solution in practically all conceived applications. Recently, the so-called second quantum revolution and quantum technologies like sensing, computing, simulation or communication are triggering a new generation of sub-classical sources to tackle such novel and challenging applications. First concepts and experimental results aimed to endow quantum cascade lasers and other infrared sources with truly quantum properties will be shown.
We will present our latest innovations on high-power diode lasers and discuss their application in quantum technologies. We show that these laser sources are key not only to explore the magic world of quantum physics, but also to drive the commercialization of exciting new applications coming along with the second quantum revolution, such as quantum computers, -sensing, -metrology and optical clocks. Compared to other laser sources such as gas- or solid-state lasers, diode lasers offer key advantages for these applications, e.g. their compactness, low weight, low energy consumption and low cost of ownership.
The second quantum revolution, Quantum 2.0, is fueled by recent progress in generating and manipulating quantum states in both light and matter, leading to new applications such as quantum sensing, computing, and communications. These new applications, which leverage unique quantum properties, such as superposition, entanglement, and measurement sensitivity of quantum states to offer fundamental advantages over classical technologies, are in principle enabled by the Quantum 1.0 technologies such as lasers. As quantum information science and technology progresses steadily from a purely academic discipline towards technology demonstrations, the imperative to transition from laboratory-grade lasers to industry-grade lasers becomes evident in the quest for scalability, robustness, improved performance, and often, reduced SWaP (Size, Weight, and Power) for field deployability. This paper provides an overview of the current state and challenges of laser-enabled quantum applications and outlines the advancements in laser technologies from macro-optics to micro-optics to integrated photonics with their prospects towards the practical realization of quantum advantage.
The exploitation of quantum mechanics has the potential to solve important challenges and \nintroduce novel technologies enabling, among others, powerful computation (which can solve \ncertain problems exponentially faster than classical computers), perfectly secure communications, \nas well as sensing and imaging with precision and resolutions not achievable by classical means. \nIn order to make use of the unique properties of quantum physics, experimental platforms \nthat provide access to, and allow the control of quantum states, need to be developed. In \nparticular, quantum systems composed of multiple parties are required, where each party is in a \ncoherent superposition of states, and where multiples of such parties are in a coherent \nsuperposition with each other (e.g. being entangled). Additionally, in order to make use of such \nentangled quantum systems, it is required that each individual party can be coherently controlled \nand measured. The usability and available quantum resources of the entangled system is related \nto its size, which is proportional to the number of entangled parties, as well as the dimensionality \nof the superposition each party is in. For this reason, there is a imminent demand to achieve, \ninvestigate, and improve the generation and control of large quantum systems, comprised of as \nmany entangled parties as possible, where each party is in an ideally high-dimensional \nsuperposition. \nMany quantum platforms are currently subject to extensive research, such as trapped ions, \nsuperconducting circuits, defect centers in solid-state crystals, mechanical oscillators, and optical \nquantum states (i.e. photons). While all platforms provide distinct advantages (as well as \nchallenges), optical photon states are of particular interest, because they can interact with other \nquantum systems, and can be transmitted over long distances while preserving their quantum \ncoherence without the need for extensive shielding. A large variety of sources for optical \nquantum states has been demonstrated, however most such implementations suffer from high \ncomplexity, ultimately limiting their scalability. Integrated photonics has recently become a \nleading platform for the compact, cost-efficient, and stable generation and processing of optical \nquantum states. However, to date, integrated quantum sources have only been able to generate \nphoton pairs, which operated on single channels, and single polarization modes. Furthermore, in \nthe few realizations of on-chip entanglement, they were limited to two entangled parties, where \neach party was in a two-dimensional superposition. These limitations of current integrated photon sources arise in large part from the concepts currently exploited to generate and control these \nstates. In particular, path-entangled sources are the most commonly used, but increasing the \nquantum state complexity requires a significant, and very challenging, increase in device \ncomplexity. There is therefore an urgent need to develop new concepts that can achieve the onchip \ngeneration of large and complex photon states without increasing source complexity, while \nstill enabling coherent quantum state control and detection. \nIn this work, we aim to address these limitations by making use of multiple frequency and \ntemporal modes within a single spatial waveguide mode (therefore readily compatible with \nstandard optical fibers) of an on-chip microring resonator. This approach is in contrast to more \ncommonly used techniques relying on path entanglement, which exploits multiple spatial modes \nand generates entanglement by means of complex waveguide structures. Working within a single \nspatial mode, we achieve the first demonstration of pure heralded single photons and entangled \nphoton pairs, which are emitted on multiple frequency modes from a single source. We then \ndemonstrate the first generation of multi-photon entangled quantum states on a photonic chip. \nFinally, by making use of the spectral multi-mode nature of optical frequency combs, we achieve \nthe generation of photon pairs in a coherent superposition of multiple frequency modes, \nrepresenting the first generation of high-dimensional entangled states on a photonic chip. \nOur work represents a significant step forward in the generation of complex quantum \nstates on a photonic chip and in a single spatial mode compatible with standard optical fibers. In \naddition, we demonstrated coherent quantum state control and manipulation for all generated \nstates by means of standard telecommunications components, which could in the future be also \nintegrated on single, monolithic chip. Our results indicate that the exploitation of integrated \noptical frequency comb sources for the generation of optical quantum states can provide a \nscalable and practical platform for quantum technologies.
Abstract When quantum theories were first formulated a century ago, who would have guessed how much technological developments originating from quantum physics shape the way we live and interact today. Whether we work on a computer, use our mobile phones, or get a diagnosis based on magnetic resonance imaging: The understanding of quantum mechanics is the basis for all these technologies. In photonics, the laser and light‐emitting diodes are prime examples, with a current market of more than 12 billion US dollars for lasers alone. Now there are new quantum technologies on the horizon, promising a second quantum revolution.
Extending beyond the achievements already made in the so-called "first quantum revolution", quantum technologies hold the potential to revolutionize the design and management of protocols for new emerging technologies in observation, communication, simulation, metrology and sensing. The second quantum revolution strives to exploit fundamental quantum properties, such as entangled quantum states, the wave nature of particles, coherent superpositions and non-classical correlations in leading edge theoretical and experimental research advancements.