# Secure Quantum Communication Technologies and Systems: From Labs to Markets
## 5 QKD Market Perspectives  
Several studies forecast a rapid growth of QKD system sales, from several million euros currently to several billion euros by 2030. Despite these optimistic predictions, several challenges remain related to the creation of a wide market for QKD systems, moving them from laboratories to a real production environment. These primarily include access to appropriate economic and human resources, and the introduction of new cost-effective technologies that can ensure performance repeatability, reliability, manufacturability at a large scale. To overcome the first issue, innovation platforms could be the ideal tool for startups and spinoff companies to gain access, so as create new technologies, standards, and protocols and share their experiences. To face the second issue (i.e., the availability of technologies deployable on large scale), the integration of optical and electronic quantum devices is a necessary step. Recent advances in photonics integration offer new opportunities in this direction. For example, silicon photonics allows the realization of miniaturized Mach-Zehnder interferometers [129] with highly stable, temperature-controlled phase shift between the two interferometers arms. Other examples are single-photon sources based on quantum dots [130], single-photon detectors able to work at room temperature [131], high-speed QRNG [132], and on-chip receivers for continuous variable systems [132]. Applications, protocols, and software are other key ingredients that require further development. Other key ingredients are those constituting a flexible network protocol stack capable of dealing with a variety of services, network topologies, and technologies, without requiring the final user to have specific quantum skills. A deeper analysis of security features at the network level is also necessary. For example, \"an advanced security analysis is required for new quantum communication protocols, including continuous-variable QKD with discrete modulation, protocols exploiting relativistic effects, or QKD protocols exploring different photonic degrees-of-freedom (frequency, time bins, polarization, paths, orbital angular momentum) [133]\". An important challenge in a QKD network is extending, in a secure way, the distance between the two end points beyond the distance of a single QKD span, which using practical thermoelectric cooling is today limited to several hundred kilometers. In principle, quantum repeaters allow long-haul communication (up to thousands of kilometers), but the technology is far from being ready for the market. Examples of candidate technologies for quantum repeaters are the already mentioned quantum repeaters based on rare earth materials [134] and on highly entangled cluster states based on quantum dots [135]. Practical implementations of MDI-QKD [136] and twin-field QKD (TF-QKD) [137] may allow network deployments where intermediate nodes can be placed in untrusted locations in the future [133]. Besides those technological aspects, initial skepticism from network providers, stakeholders, venture capitalists, and the general public could be a non-negligible delay factor in the introduction of QKD technologies. Devices and systems based on quantum physics are often considered exotic technologies that are not economically attractive and not fully understood. Figure 3[138] shows expected barriers acquired through surveys to companies in various market segments. QKD systems will have to demonstrate that they can compete with standard encryption algorithms and complement conventional networks, giving a plausible return of investment in the short and medium time periods. There is also a growing view that excessively stringent regulations may impede the setting up of new businesses. Regulation and standardization, however, are essential for QKD to succeed. QKD security indeed depends on the implementation of interoperable protocols with well understood and certified security properties.