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Four EMRP and EMPIR collaborative projects prepare for the photonics measurement challenges required by the ‘second quantum industrial revolution’.
Co-authors: Christopher Chunnilall (NPL), Ivo Pietro Degiovanni (INRiM), Stefan Kück (PTB) and Marek Šmid (CMI)
Many existing technologies such as microprocessors, solid state imaging devices and lasers are based on quantum physics. Just as classical physics underpinned the Industrial Revolution, these “quantum 1.0” technologies underpinned the Information Age. The emerging “quantum 2.0” technologies that rely on the creation, detection and manipulation of a single or a few quantum states and more subtle, less familiar aspects of quantum mechanics, such as superposition and entanglement, have the potential to create a “second quantum revolution”. Günther H. Oettinger, Commissioner Budget & Human Resources and former Commissioner for the Digital Economy and Society, outlined in the Commission’s plan that this second revolution “should lead to devices with far superior performance and capabilities for sensing, measuring and imaging; for communication, simulation and computing. Quantum technologies ultimately are expected to open new opportunities to address grand challenges in such fields as energy, health, security and the environment. Some are already starting to be commercially exploited. Others may still require years of careful research and development. Yet others we cannot even imagine today.” Over 2 billion euro funding has been provided by the EU Quantum Flagship and national programmes in the UK, Germany and the Netherlands to support the commercialisation of quantum 2.0 technologies.
Quantum metrology (metrology is the science of measurement) aims to develop the new measurement capability needed for the commercial success of these quantum technologies and, also, to exploit quantum-enhanced techniques to surpass the sensitivity, precision and accuracy of conventional techniques. In photonics, a major challenge is to bridge the traceability gap from the International System of Units (SI) currently established in the classical regime to the single-photon level where quantum photonic devices operate. Calibrating the quantum features and behaviour of these devices requires not just translating traditional measures to the single-photon level, but the development of new metrics, methods and instrumentation for quantifying them.
Four EURAMET photonics projects have each brought together experts from different countries in order to tackle the measurement challenges in this highly technical area. Sharing their combined expertise and resources in these collaborations have enabled EURAMET and the National Metrology Institutes and Designated Institutes to make faster and more efficient progress than if the institutes worked in isolation.
The EURAMET Projects
Since 2010, EURAMET has significantly boosted efforts to develop a robust metrology infrastructure supporting emerging quantum photonic technologies. Major progress has been achieved through the following projects within the European Metrology Research Programmes, EMRP and EMPIR:
- Metrology for industrial quantum communication technologies (IND06, MIQC)
- Optical metrology for quantum enhanced secure telecommunication (14IND05, MIQC2)
- Single-photon sources for quantum technologies (EXL02, SIQUTE)
- Single-photon sources as new quantum standards (17FUN06, SIQUST)
These have primarily focussed on the following topics:
1. Quantum communications (projects MIQC and MIQC2)
Current algorithmic key distribution schemes are vulnerable to new mathematical insight, powerful computers, or future quantum computers. Elsewhere, work is underway to develop new secure mathematical algorithms (“post-quantum” cryptography). However, it will be very hard to provide security against all possible future quantum computer cryptanalysis. Quantum key distribution (QKD) uses quantum states of light to communicate between two distant parties, creating a shared secret encryption key that can then be used to secure their conventional communications. QKD encodes the key using a physical process, and key security depends on the physical performance of the QKD system. This means that a QKD key is future-proof – if it is going to be hacked, that has to happen at the time of creation.
Physical characterisation of QKD hardware is therefore essential for security assurance. The most advanced QKD systems are based on the use of single photons created by attenuating laser pulses; other QKD approaches are being rapidly developed, including those based on multi-photon pulses and on entangled photons. Projects MIQC and MIQC2 developed reliable, SI-traceable methods for characterising QKD components such as attenuated laser sources, single-photon detectors and modulators. These methods have been input to the ETSI Industry Specification Group on QKD (ETSI is one of the three officially recognised European Standardisation Organisations), where its National Measurement Institute members lead the drafting of protocols for testing single-photon QKD systems.
2. Quantum imaging, sensing and metrology (projects SIQUTE and SIQUST)
These technologies are not as commercially advanced as those in secure communications, but they also have tremendous market prospects.
Quantum imaging exploits the properties of non-classical states of light to achieve unique imaging performance in terms of resolution and contrast, and also surpass conventional limits of sensitivity and resolution, especially but not only, when a small number of photons is measured. These imaging protocols have the potential to trigger major advances in applications such as microscopy and biophotonics, and provide an important opportunity for the study of vision mechanisms at the single photon level.
Quantum sensors exploit the interactions of tailored quantum states with the environment. This could lead to the development of high-precision electric and magnetic field sensors for applications such as imaging the brain and individual neurons and for materials analysis in the semiconductor industry.
‘Squeezed light’ is an application of quantum physics that is used in gravitational wave detectors to improve phase measurement in interferometry. This technology is expected to be widely disseminated to improve the signal-to-noise ratio for phase-encoded optical signals to increase data rates in telecommunications, and in metrology for improved industrial dimensional measurements. EMPIR project ‘Light-matter interplay for optical metrology beyond the classical spatial resolution limits’ (17FUN01, BeCOMe) is investigating approaches connected with super-resolved and sub-shot noise imaging for the latter.
3. Single-photon sources and detectors (projects SIQUTE, SIQUST, MIQC and MIQC2)
Single-photon sources and detectors are crucial components in the technologies described above. True, deterministic, single-photon sources (as opposed to attenuated lasers) and methods to thoroughly characterise single-photon sources and detectors were developed in the projects and will accelerate innovation in quantum photonic technologies.
The metrology and scientific communities will also benefit from the increased accuracy and robustness of scale artefacts designed for the low-photon-flux regime; the developed (standard) single-photon sources may be based on sub-micrometre solid-state structures or impurity states encapsulated in micrometre-scale optical devices and packaged in 19-inch rack modules. They will be the basis for a realisation of the optical radiant flux in terms of photon rate, i.e. a countable number of photons per unit time, with selectable emission rates, and will also be very useful for educational purposes in academia and schools.
4. EURAMET Comparisons (projects MIQC2 and SIQUST)
The Consultative Committee for Photometry and Radiometry and projects MIQC2 and SIQUST initiated a series of pilot study comparisons aiming, with partners from SIM (Inter-American Metrology System) and APMP (Asia Pacific Metrology Program), to validate the developed standards and methodologies in a global framework. The first stage included the most relevant quantities such as quantum efficiency of single-photon detectors and second-order correlation of single-photon sources, at 850 nm and in the telecom spectral range. The results from the comparisons so far completed (Nature Physics research highlight, Feasibility study report, Single-photon source pilot study report) agree within uncertainty and mark the first steps towards international accepted metrics and measurement scales, essential for international trade in products based on these technologies.
Calibration services for measurements at the single-photon level will be routinely provided by European NMIs and DIs, and the further development of quantum technologies will continue to drive the need for new quantum metrics, standards and metrological facilities.
European Metrology Network for Quantum Technologies
The European Metrology Network for Quantum Technologies will provide active co-ordination of European measurement science research to maintain competitiveness in the field of quantum technologies. By promoting and facilitating knowledge sharing, collaboration with stakeholders and the uptake of measurement science in the development of quantum technology, the network will establish globally accepted measurement services for quantum technologies and devices.
EMPIR projects are co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.
EMRP joint research projects are part of EURAMET’s European Metrology Research Programme. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.
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