Integrated Photonics: Pioneering the Second Quantum Revolution in Communication and Metrology

Integrated photonics has significantly transformed quantum technologies over the past two decades, playing a crucial role in the ongoing second quantum revolution. This technology, which involves controlling the flow of photons on a chip, has contributed to the rapid growth of photonics and optical communications. It has also paved the way for the emergence of quantum photonics, the science dedicated to the coherent manipulation of photons. Integrated photonic solutions have been instrumental in modern telecommunications and have enabled the development of practical real-field prototypes in the field of quantum information.

What is the Role of Integrated Photonics in Quantum Communications and Metrology?

Integrated photonics has significantly transformed the field of quantum technologies over the past two decades. This technology is currently at the forefront of the ongoing second quantum revolution, which is a timely opportunity for a comprehensive review and exploration of the directions taken by integrated quantum photonics. This perspective is based on recent advances and discusses the current challenges and future trends related to different technological platforms. Key examples will be considered across various subfields, including quantum communication, quantum metrology, and quantum memories. The main objective is to provide a forward-looking discussion ranging from state-of-the-art developments to open challenges of the field.

How Has Quantum Photonics Evolved?

Since ancient times, the unique properties of light have attracted the interest of scientists and shaped the history of science. Thanks to the pioneering works of the founders of quantum physics in the beginning and throughout the 20th century, we have understood that light is inherently quantum. The current situation is undergoing a profound change. As JP Dowling suggested in 2003, we are currently in the midst of a second quantum revolution. The first quantum revolution gave us new rules that govern physical reality. The second quantum revolution will take these rules and use them to develop new technologies. The conceptual and physical foundations of this revolution are quantum superposition and entanglement, which offer new possibilities in computation, communication, and even metrology. Practical advantages of these technologies have already been demonstrated.

What is the Role of Photons in Quantum Technologies?

In this context, photonics will continue to play a major role. Photons serve as ideal two-level systems; they experience minimal noise, support high-speed transmission, and are relatively simple to manipulate and detect. This has significantly contributed to the rapid growth of the fields of photonics and optical communications in the last three decades of the past century, relying predominantly on the non-quantum properties of light where the field can be described as a classical electromagnetic wave. Thus, it has provided fertile ground for the emergence of quantum photonics. Quantum photonics is the science dedicated to the coherent manipulation of photons, i.e., the individual quanta of the light field, and its applications.

How Does Integrated Photonics Work?

Indeed, as it was for classical photonics, microelectronics, and other fields, integration seems to be the key to scalability and therefore to many real-world applications. An introduction to integrated photonics can be helpful in understanding its similarities and differences with traditional electronic circuits. While integrated electronics involves controlling the flow of electrons on a chip, integrated photonics does the same with photons. The high-frequency range of the electromagnetic field of light significantly increases the bandwidth and speed of the circuit without generating significant heat, making photonic integrated circuits much more efficient than their electronic counterparts.

What is the Impact of Integrated Quantum Photonics?

Integrated photonic solutions, which have been the key to modern telecommunications, have similarly acted as enabling technologies for the new field of quantum information. They have dramatically boosted experimental quantum photonics to break through laboratory proof of principles and to evolve from unscalable photon sources, modest efficiency single-photon detectors, and optical circuits constructed from bulk elements bolted to room-sized optical tables toward practical real-field prototypes. Essentially, the lever effect of guided wave optics lies in enhancing the efficiency of optical-optical and electro-optical nonlinear interactions, but also the possibility of merging several functions on a single chip, drastically simplifying the realization and use of interferometric quantum electro-optical circuits.