Over the past few decades, THz technology has made considerable progress, evidenced by the performance of current THz sources and detectors, as well as the emergence of several THz applications. However, in the realm of quantum technologies, the THz spectral domain is still in its infancy, unlike neighboring spectral domains that have flourished in recent years. Notably, in the microwave domain, superconducting qubits currently serve as the core of quantum computers, while quantum cryptography protocols have been successfully demonstrated in the visible and telecommunications domains through satellite links. The THz domain has lagged behind in these impressive advancements. Today, the current gap in the THz domain clearly concerns quantum technologies. Nonetheless, the emergence of quantum technologies operating at THz frequencies will potentially have a significant impact. Indeed, THz radiation holds significant promise for wireless communications with ultimate security owing to its low sensitivity to atmospheric disturbances. Moreover, it has the potential to raise the operating temperature of solid-state qubits, effectively addressing existing scalability issues. In addition, THz radiation can manipulate the quantum states of molecules, which are recognized as new platforms for quantum computation and simulation with long range interactions. Finally, its ability to penetrate generally opaque materials or its resistance to Rayleigh scattering are very appealing features for quantum sensing. In this perspective, we will discuss potential approaches that offer exciting prospects for generating and detecting non-classical states of THz light, thereby opening doors to significant breakthroughs in THz quantum technologies.
Over the past few decades, THz technology has made considerable progress, evidenced by the performance of current THz sources and detectors, as well as the emergence of several THz applications. However, in the realm of quantum technologies, the THz spectral domain is still in its infancy, unlike neighboring spectral domains that have flourished in recent years. Notably, in the microwave domain, superconducting qubits currently serve as the core of quantum computers, while quantum cryptography protocols have been successfully demonstrated in the visible and telecommunications domains through satellite links. The THz domain has lagged behind in these impressive advancements. Today, the current gap in the THz domain clearly concerns quantum technologies. Nonetheless, the emergence of quantum technologies operating at THz frequencies will potentially have a significant impact. Indeed, THz radiation holds significant promise for wireless communications with ultimate security owing to its low sensitivity to atmospheric disturbances. Moreover, it has the potential to raise the operating temperature of solid-state qubits, effectively addressing existing scalability issues. In addition, THz radiation can manipulate the quantum states of molecules, which are recognized as new platforms for quantum computation and simulation with long range interactions. Finally, its ability to penetrate generally opaque materials or its resistance to Rayleigh scattering are very appealing features for quantum sensing. In this perspective, we will discuss potential approaches that offer exciting prospects for generating and detecting non-classical states of THz light, thereby opening doors to significant breakthroughs in THz quantum technologies.
The terahertz (THz) regime of electromagnetic radiation, spanning frequencies from 0.1 to tens of THz, has found widespread use in communication, sensing, quality control, and biomedical applications. Quantum realm of THz domain is, however, still at an earlier development stage and mostly referenced in the context of applied technologies for single-photon generation and detection, with rarer examples of exploration of quantum phenomena. Recent advances in cryogenic hybrid quantum systems suggest that THz radiation may play a pivotal role in emerging quantum technologies. These systems, which require operation at milliKelvin temperatures, offer new opportunities for quantum memory, frequency transduction, and precision measurements, with THz radiation enabling access to molecular vibrational, rotational, and librational transitions. Despite progress in THz components at low temperatures, there remains a critical gap in the systematic integration of THz technologies within sub-Kelvin cryogenic platforms such as dilution refrigerators and adiabatic demagnetization systems. This review presents a comprehensive roadmap for the development of THz photonics in extreme cryogenic environments, addressing implementation strategies, material considerations, waveguide and fiber technologies, and quantum-compatible detection schemes. We further highlight prospective applications in quantum optics, superconductivity, and fundamental physics, aiming to establish THz photonics as a versatile tool for controlling and probing quantum states in sub-Kelvin regimes.
The terahertz (THz) regime of electromagnetic radiation, spanning frequencies from 0.1 to tens of THz, has found widespread use in communication, sensing, quality control, and biomedical applications. Quantum realm of THz domain is, however, still at an earlier development stage and mostly referenced in the context of applied technologies for single-photon generation and detection, with rarer examples of exploration of quantum phenomena. Recent advances in cryogenic hybrid quantum systems suggest that THz radiation may play a pivotal role in emerging quantum technologies. These systems, which require operation at milliKelvin temperatures, offer new opportunities for quantum memory, frequency transduction, and precision measurements, with THz radiation enabling access to molecular vibrational, rotational, and librational transitions. Despite progress in THz components at low temperatures, there remains a critical gap in the systematic integration of THz technologies within sub-Kelvin cryogenic platforms such as dilution refrigerators and adiabatic demagnetization systems. This review presents a comprehensive roadmap for the development of THz photonics in extreme cryogenic environments, addressing implementation strategies, material considerations, waveguide and fiber technologies, and quantum-compatible detection schemes. We further highlight prospective applications in quantum optics, superconductivity, and fundamental physics, aiming to establish THz photonics as a versatile tool for controlling and probing quantum states in sub-Kelvin regimes.
Abstract Terahertz (THz) technology is a rapidly developing field that explores the use of electromagnetic waves in the THz frequency range. The unique properties of THz waves have great application prospects in electromagnetic sensing, security inspection, non-destructive testing, medical diagnostics, biology, high-speed wireless communication, space science and so on. At present, the application of THz technology is still under continuous research and development, and its broad scientific prospects are recognized worldwide. THz frequency falls into the gap on the electromagnetic spectrum of electronics and optics, thus both classic microwave and optical technologies cannot be directly applied to the THz systems. New components, circuits and application systems are being developed for THz technology. Superconductivity is a quantum mechanical phenomenon and offers unique advantages for applications in high-frequency electromagnetic domains. Novel superconducting quantum devices are being exploited for THz wave radiation and detection, and many THz application systems. The high-T c superconducting (HTS) electronic devices have great potential in emerging THz technologies due to its very high-energy bandgap (well into THz regions) and much relaxed cooling requirement, and they offer strong prospect for the development of practical and portable THz systems. This paper provides an overview of the state-of-art development of HTS THz quantum devices and their application for THz sensing, imaging and communication. The review will start with a brief introduction about cutting-edge THz technology, the fundamental of superconductivity, Josephson effects and the HTS Josephson junctions. Then, the research progress and the latest achievement of HTS Josephson THz emitters, detectors and mixers will be reviewed, followed by their application examples in some THz systems. Finally, the conclusion, challenges and outlooks of the HTS technologies in THz applications are discussed.
While the commercial deployment of 5G networks and beyond is a reality, the first work for the definition and study of 6G networks has started. The scientific community agrees that these networks will be characterised by a very high spatial density of access points, heterogeneity of access technologies, an increased number of users per access point, and demand for ubiquitous connectivity that must combine ultra-low latency, very high bandwidth, and high energy efficiency [1, 2]. Among the emerging challenges, holographic communications, high-precision manufacturing, the ubiquitous introduction of intelligence, and the incorporation of new technologies based on sub-terahertz (THz) or Visible Light Communications (VLC) are real issues. These are taking place in a truly three-dimensional coverage framework, integrating terrestrial and aerial radio to meet the needs with cloud-based capabilities where and when needed (on-demand). Radio frequencies are used in wireless telecommunications, but the need for very high throughput requires wider bandwidths, hence very high frequencies, in particular THz bands. Moving to a higher frequency range—from 100 GHz to 10 THz—is expected to significantly increase the bandwidth of the radio channel, which will make it possible to serve a significant number of users. In this case, we are not talking about the connection of cell phones, tablets, or computers (and even smart cars)—we are considering the use of Internet of Things (IoT) devices, which within one base station can be quite a lot. Therefore, the technologies for beamforming, device location, etc., developed for the 5G generation that is just being implemented now should also remain but will be used at higher frequencies [3]. For which 6G is primarily intended, IoT solutions have been given a particular name: ‘human-machine-things’. They involve three elements in the system: a person as a physical carrier; an intelligent device with which the person interacts; collects data and executes commands from an application running on the person's device [4]. The 6G radio networks will provide the means of communication and data gathering necessary to accumulate information. Still, a system's approach will be required for the 6G technology market as a whole involving data analytics, artificial intelligence (AI), and next-generation computation capabilities via HPC and quantum computing [3, 5]. This tremendous amount of data may be harnessed, with strong processing and learning capabilities, to manage the network at different levels. To this end, quantum computing methods can play a significant enabling role and can provide a guaranteed security platform. Towards provisioning this massive connectivity and efficiently processing the voluminous data available at the user and network sides, quantum-powered computing methods have a strong potential in realising the ambitions of a service-driven, fully intelligent 6G communication network. There is every reason to believe that the integration of quantum technology can improve the throughput, efficiency, and security of 6G networks. In addition to the advantages mentioned above, this technology also has benefits in computing speed, guaranteed security, and minimal storage requirements. This makes it ideally suited for various future quantum communication network applications. Research is needed on many fronts to evaluate the potential opportunities of quantum computing in 6G applications. In 5G, a functional division is operated in both the RAN and core networks to meet the ultra-low latency and ultra-high efficiency requirements of 5G verticals. Notably, RAN functions are split into cloud-deployed services with interfacing capabilities. This new architecture has a significant impact on the efficient implementation of security processes [6]. One of the key challenges in deploying secure 5G networks is analysing how current cryptographic algorithms for secure authentication and data transmission can adapt to provide secure authentication between services and secure data encryption while ensuring that stringent efficiency requirements are met [7]. The powerful parallel processing capability of quantum search algorithms can be leveraged to solve large-scale wireless optimisation problems. (1) Is this ‘beyond 5G?’ This topic is highly exploratory and undoubtedly beyond the boundaries of core 5G R&D. (2) What are the new features and key challenges? Classically, the mutual information between the channel input and output must be maximised. For quantum channels, the capacity must be redefined. Quantum channels can increase the achievable capacity. As a result, error correction without redundancy is possible on noisy channels. Quantum computers can enable exponentially complex combinatorial ML decoding in classical systems [5, 6]. To cope with latency-critical scenarios such as automated cars and medical applications, communication must be accomplished in a concise time. Achieving latency of only a few milliseconds is a real challenge. To achieve low latency and ultra-high reliability, it is essential to develop powerful high-end processors that consume little power. Quantum computing seems to be a reliable solution to this issue [8]. With variable quality of service (QoS) requirements, a variable radio resource must be allocated to the user. This can be of variable bandwidth, variable power, or both. Another challenging aspect of 6G is that with the propagation frequency, the signal can attenuate quickly and have a high penetration loss at high frequencies [9]. The signal is also automatically attenuated when accessing homes, residences, or workplaces. As the frequency increases, radio waves attenuate and may have difficulty penetrating the walls of buildings and homes while affecting users' QoS requirements. Therefore, it is very important to develop stable, fast and accurate quantum algorithms to handle 6G communication requirements by dynamically allocating variable resources [10]. The current 5G standard does not address the issue of quantum computing but relies on traditional cryptography. The development towards cloud and edge native infrastructures is expected to continue in 6G networks. While large-scale quantum computing can be expected to take a longer duration, it is time to prepare for the shift to cryptography that is secure in the post-quantum world. According to current knowledge, contemporary symmetric cryptography remains secure for the most part, even after the advent of quantum computing. Furthermore, authentication by a physical layer signature, such as RF fingerprinting, and some other technologies, such as randomisation of MIMO transmission coefficients, coding, etc., could potentially be used in 6G [5, 11]. Whether it is for the optimisation of heterogeneous resources in 6G networks that result in the solution of ‘NP-complete’ combinatorial problems, for the compensation of non-linear effects of a communication chain or the optimisation of MIMO transmitter pre-coding matrix, future network nodes and devices will have to be equipped with learning and decision-making capabilities through AI and machine learning, so that they autonomously optimise their operation in response to changes in the environment [5]. In this context, the use of optimisation techniques based on quantum computing and AI applied to the field of 6G networks could be of considerable interest. Besides, quantum computing allows NP-hard optimisation problems to be solved in linear time, making it possible to solve and execute network optimisation problems in a much faster time, even in real-time [5, 11]. Regulatory and standardisation work will impact our future technology solutions in 5G networks and beyond. Protecting individual privacy and identity has long been a challenge for standards bodies, as countries have very different perspectives and regulations in this area. International standards bodies such as JTC 1 have committees working on privacy frameworks and are making progress, but there is still much to be done [13]. To conclude, we believe that our readers will find this opinion piece useful in giving an overview of the importance of Quantum Computing/communications in shaping the next communication systems and its security platforms. This is a technology in its infancy and a lot of research remains to be carried out to achieve sustainable solutions and overcome the current challenges. The use of intelligent systems (AI, ML and other techniques) will be essential in achieving solutions faster and providing sustainable outcomes. But IoT devices as well as cloud and edges nodes must be AI-ready and be able to support the use of intelligent algorithms.
Quantum technologies are at the cusp of a new technological revolution, with quantum computing and quantum sensing emerging as two of its most transformative domains. This review paper provides an in-depth analysis of these fields, exploring their fundamental principles, hardware implementations, and the challenges that hinder their widespread adoption. Quantum computing, leveraging superposition and entanglement, promises to solve intractable computational problems in areas like drug discovery, materials science, and cryptography. Concurrently, quantum sensing exploits the inherent sensitivity of quantum systems to external perturbations, enabling unprecedented precision in metrology, medical diagnostics, and navigation. We delve into the diverse hardware platforms for each field, including superconducting qubits, trapped ions, NV centers in diamond, and cold atoms. A central theme of this review is the symbiotic relationship between quantum computing and quantum sensing, illustrating how advancements in one area directly accelerate progress in the other. Finally, we discuss the current state of the art, identify key technical and engineering challenges, and provide an outlook on future directions and potential societal impacts.
Matter-based two-level quantum systems are fundamental building blocks of quantum technologies, underpinning applications in quantum computing, simulation, communication, and sensing. Today, most of these two-level quantum systems, including Rydberg atoms, trapped ions, superconducting circuits, molecules, and quantum dots, involve transition frequencies in microwave or optical domains. However, extending their transition frequency to the THz spectral range could provide numerous benefits, leveraging the unique properties of THz radiation. Here, we show that an hBN-encapsulated graphene double quantum dot realizes a two-level system with a transition frequency in the THz spectral range. Using low-temperature transport spectroscopy in the dark combined with modeling based on nonequilibrium Green's function formalism, we demonstrate the formation of an artificial molecule, featuring bonding and antibonding states separated by an energy of up to 0.6 meV, corresponding to a resonance frequency of 0.145 THz. This approach provides direct access to important parameters of open double quantum dot systems, including tunneling rates, offering a practical alternative to conventional techniques such as photon-assisted tunneling, which are challenging to implement at THz frequencies. The realized 2D-material-based THz two-level system, compatible with direct on-chip integration, could serve as a key building block for future THz quantum technologies. Furthermore, by involving a single-electron transition, coupling these devices to a THz resonator could enable the exploration of ultra-strong light-matter interactions at the fundamental limit of a single transition coupled to a single cavity, beyond the reach of existing THz quantum systems based on collective transitions.