Quantum optical information technologies such as key distribution systems for secure communications, which are based on the discrete and quantum properties of photons, are now commercial products. Market take-up of these and other developing quantum technologies will be compromised unless there are traceable measurements to validate the performance of these devices. We highlight some ongoing collaborative research that will provide the required high accuracy techniques for the few and single photon regime, including operation at telecom wavelengths.
Quantum optical information technologies such as key distribution systems for secure communications, which are based on the discrete and quantum properties of photons, are now commercial products. Market take-up of these and other developing quantum technologies will be compromised unless there are traceable measurements to validate the performance of these devices. We highlight some ongoing collaborative research that will provide the required high accuracy techniques for the few and single photon regime, including operation at telecom wavelengths.
Industrial technologies based on the production, manipulation, and detection of single and entangled photons are emerging, and quantum key distribution via optical fibre is one of the most commercially-advanced. The National Physical Laboratory is developing traceable performance metrology for the quantum devices used in these technologies. This is part of a broader effort to develop metrological techniques and standards to accelerate the development and commercial uptake of new industrial quantum communication technologies based on single photons. This presentation will give an overview of the work carried out at NPL and within the wider European community, and highlight plans for the future.
The generation, measurement, and manipulation of light at the single- and few-photon levels underpin a rapidly expanding range of applications. These range from applications moving into the few-photon regime in order to achieve improved sensitivity and/or energy efficiency, as well as new applications that operate solely in this regime, such as quantum key distribution and physical quantum random number generation. There is intensive research to develop new quantum optical technologies, for example, quantum sensing, simulation, and computing. These applications rely on the performance of the single-photon sources and detectors they employ; this review article gives an overview of the methods, both conventional and recently developed, that are available for measuring the performance of these devices, with traceability to the SI system.
Photons are very promising resources for the whole field of quantum information processing. Bulk optics are currently not suitable for the realization of complex quantum optical schemes due to several drawbacks. The ongoing miniaturization of photonic structures due to the availability of sophisticated nanofabrication has provided huge opportunities for physical research of novel phenomena in nanophotonic systems and quantum technological applications. These include quantum information processing such as quantum computing, quantum communication, quantum metrology, and quantum sensing. Quantum communication is already quite advanced with several quantum key distribution (QKD) systems commercially available offering absolute security. Photonic quantum technologies are enabling breakthroughs in experimental tests of quantum physics and are close to practical applications of quantum technologies in imaging, secure communications, ultrasensitive metrology and quantum computing. There are several advantages to encoding a quantum bit onto a photon: the preparation and manipulation of single photons is easy, and the photonic qubit is a natural candidate for quantum imaging and communications. Furthermore, the qubit can be encoded in various degrees of freedom such as on the position, phase, time-bin, energy, angular momentum, polarization of the photon—or a combination of these. This flexibility leads to enormous opportunities for scientific exploration and in practical applications. This special issue on “Photonic Quantum Technologies” presents selected papers on photonic quantum systems from leading groups in the world. The articles represent a flavor of the cutting-edge research that is going on in this area. The studied material systems range from molecules to semiconductor quantum emitters. A major challenge is the design of telecom photon emitters with high efficiency, good yield, spectral purity, stability and the possibility of mass manufacture. We believe that this Special Issue will provide an overview of recent exciting developments in the field of photonic quantum technologies, serving to keep researchers up-to-date with the latest progress and spurring on new concepts in this field.
Quantum Key Distribution, a fundamental component of quantum secure communication that exploits quantum states and resources for communication protocols, can future-proof the security of digital communications, when if advanced quantum computing systems and mathematical advances render current algorithmic cryptography insecure. A QKD system relies on the integration of quantum physical devices, as quantum sources, quantum channels and quantum detectors, in order to generate a true random (unconditionally secure) cryptographic key between two remote parties connected through a quantum channel. The gap between QKD implemented with ideal and real devices can be exploited to attack real systems, unless appropriate countermeasures are implemented. Characterization of real devices and countermeasure is necessary to guarantee security. Free-space QKD systems can provide secure communication to remote parties of the globe, while QKD systems based on entanglement are intrinsically less vulnerable to attack. Metrology to characterize the optical components of these systems is required. Actually, the “Optical metrology for quantum-enhanced secure telecommunication” Project (MIQC2) is steering the metrological effort for Quantum Cryptography in the European region in order to accelerate the development and commercial uptake of Quantum Key Distribution (QKD) technologies. Aim of the project is the development of traceable measurement techniques, apparatus, and protocols that will underpin the characterisation and validation of the performance and quantum-safe security of such systems, essential steps towards standardization and certification of practical implementations of quantum-based technologies.
Quantum photonics technologies have realized great advancements over the past decade. Quantum photonic integrated circuits, devices which incorporate single-photon emitters, detectors and optical components on a single device, are already being implemented in quantum computing and networking hardware. The verification and validation of system performance, including the characterization of single-photon sources and the efficiency of single-photon detectors is an ongoing challenge, especially for integrated devices. One approach to characterizing a single-photon source is to measure the optical power of the emitted photons, which can be applied in turn to the characterization of on-chip components within an integrated quantum photonics platform. This presentation will address the development of metrological devices and measurement techniques, where an ultra-sensitive radiometer chip directly measures the optical power of photons emitted from a quantum dot single-photon source. This measurement technique demonstrates the feasibility of implementing optical power measurements of on-demand single photon sources in the verification and validation of quantum photonics systems.
Quantum information science has emerged to consider what additional power and functionality can be realized in the encoding, transmission, and processing of information by specifically harnessing quantum mechanical effects. Anticipated technologies include quantum key distribution, which offers perfectly secure communication; quantum metrology, which allows more precise measurements than could ever be achieved without quantum mechanics; and quantum lithography, which could enable fabrication of devices with features much smaller than the wavelength of light. Perhaps the most profound future technology is a quantum computer that promises exponentially faster operation for particular tasks. Of the various physical systems being pursued, an all-optical quantum computer, which encodes quantum information in single photons, has emerged as a leading approach. Here we give a brief review of this field, focusing on some of our recent work.