Quantum key distribution (QKD) is one of the most commercially-advanced quantum optical technologies operating in the single-photon regime. The commercial success of this disruptive technology relies on customer trust. Network device manufacturers have to meet stringent standards in order to ensure the operational security of their devices. The National Physical Laboratory (NPL) and the University of Bristol (Bristol) are working to produce a suite of tests to determine the operating characteristics and implementation security of chip-scale quantum devices designed for security purposes. These tests will inform and provide assurance to potential customers of such devices. Results from initial measurements performed on the Bristol chip-scale transmitter and receiver are presented, with the aim of informing the development of the system.
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.
This article [Opt. Eng.. 53, (8 ), 081910 (2014)] was originally published on 10 July 2014 with an error in the denominator of Eq. (6). The denominator should be the letter eta, as shown in the corrected equation below:
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.
Randomness is of fundamental importance in various fields, such as cryptography, numerical simulations, or the gaming industry. Quantum physics, which is fundamentally probabilistic, is the best option for a physical random number generator. In this article, we will present the work carried out in various projects in the context of the development of a commercial and certified high speed random number generator.
The full characterisation of photon counting detection systems is important because it allows the identification and
subsequent adoption of the system with the optimum performance. It also allows the uncertainty contributions
introduced by a particular detection system to be calculated and used in the estimation of the combined uncertainty of the
measurement in which that detection system is being used. The Optical Metrology Group at the National Physical
Laboratory (NPL) has assembled dedicated facilities, which are able to characterise the critical operating parameters of
photon counting systems anywhere in the 250 nm to 1600 nm wavelength region. These include the absolute and relative
spectral responsivity over the wavelength range of interest, the spatial uniformity of response at the wavelengths of
interest, the deviation from a true linear response as a function of incident radiant power/irradiance and the stability of
response as a function of time or ageing. Using these facilities, the performance of a number of photon counting systems
has been evaluated in an effort to identify the most appropriate detector technologies for the various radiometric
applications NPL is currently addressing. This document describes the dedicated facilities which exist at NPL and
highlights how they are being used to provide traceable measurements of the key performance parameters of photon
counting systems. Examples of characterisations of photon counting systems are presented.
Low photon flux measurements are widely used in the fields of biology, nuclear physics, medical physics and
astrophysics. This paper will highlight the key requirements and considerations needed for accurate, traceable
measurement at these low light levels. A new driver for these techniques is the rapidly advancing field of optical
quantum information processing1 which requires the development of single photon counting detectors, in addition to the
wider use of optical technologies in the photon counting regime. The paper will present the results of the measurement of
the quantum efficiency of a channel photomultiplier detector using an absolute radiometric technique based on correlated
photons produced in non-linear crystals. Case studies will also be presented to illustrate this work.
The United Kingdom scales for diffuse reflectance are realized using two primary instruments. In the 360 nm to 2.5 μm spectral region the National Reference Reflectometer (NRR) realizes absolute measurement of reflectance and radiance factor by goniometric measurements. Hemispherical reflectance scales are obtained through the spatial integration of these goniometric measurements. In the mid-infrared region (2.5 μm - 55 μm) the hemispherical reflectance scale is realized by the Absolute Hemispherical Reflectometer (AHR). This paper describes some of the uncertainties resulting from errors in aligning the NRR and non-ideality in sample topography, together with its use to carry out measurements in the 1 - 1.6 μm region. The AHR has previously been used with grating spectrometers, and has now been coupled to a Fourier transform spectrometer.
Many of the schemes utilizing photon states under investigation for Quantum Information Processing (QIP) technology involve active and passive optical components. In order to be able to establish fidelity levels for these schemes, the performance of these optical components and their coupling efficiencies require careful and accurate characterization. Correlated photons, the basis of entangled photon states, offer a direct means of measuring detector quantum efficiency and source radiance in the photon counting regime. Detector and source calibration by correlated photon techniques therefore address some of the key factors critical to QIP technology and the developing techniques of correlated/entangled photon metrology. Work is being undertaken at NPL to establish the accuracy limitations of the correlated photon technique for detector and source calibration. This paper will report on investigations concerning the characterization of silicon avalanche photodiode detectors using the correlated photon technique.
Many of the schemes under study for Quantum Information Processing technology based on photon states involve active and passive optical components as well as detectors. In order to able to establish fidelity levels for these schemes, the performance of the optical components and the quantum efficiency (q.e.) of the detectors require careful and accurate characterization. Correlated photons produced from spontaneous parametric downconversion, which are also the basis of entangled photon states, conveniently offer a direct means of measuring detector q.e. in the photon counting regime, while stimulated parametric downconversion can be used to measure source radiance. Detector and source calibration using correlated photon techniques therefore address some of the key issues critical to the development of QIP technology and the development of correlated/entangled photon metrology. This paper reports work being undertaken at NPL to establish the accuracy limitations of these correlated photon techniques. Significant sources of uncertainty are the need to measure losses due to any optical components used and the requirement to obtain and maintain good geometrical and spectral alignment.
Thermal barrier coatings are widely used in heat engines for improving efficiency by allowing higher operating temperatures; yttria stablised zirconia is the most widely used material. Their use has been extended to rotating parts, in particular to gas turbine engine blades, and any loss of coating would represent a major problem. During deposition of the coating, a thin (< 1μm) alumina layer grows due to oxidation of the bondcoat, and it is this alumina layer which promotes bonding between the coating and the coated substrate. The spectral shape and position of the R-line fluorescence of Cr3+ ions normally present in small amounts in the alumina is sensitive to stress, temperature and other
environmental effects. Stress is the key factor determining spallation, and piezospectroscopy refers to the use of spectroscopic measurement to determine stress within a material. Measurements have been carried out as a function of various ageing treatments in order to evaluate the potential of the technique to be a non-destructive probe for determining the onset of spallation. Interpreting the changes in the fluorescence spectra requires the use of sophisticated curve-fitting techniques and therefore requires reliable and accurate measurements. This paper will discuss these measurement requirements and their potential for development into a non-destructive tool for lifetime prediction of these structures.
The National Physical Laboratory (NPL) realises and disseminates the UK spectrometric scales from 200 nm to 56 μm wavelength. Its mid-infrared (MIR) regular and hemispherical reflectance and transmittance scales, and transfer standards for the wavenumber and ordinate calibration of MIR spectrometers are realised from 2.5 μm to 56 μm using specially modified grating spectrometers.
This paper will discuss a technique, recently developed at NPL, for the direct absolute realization of the hemispherical reflectance scale. This scale was previously based on a relative method using an absolutely calibrated mirror and published data for BaSO4. The new method has given an improved value for the pure BaSO4 to underpin the relative method. It opens up new applications as it can be applied to types of sample not previously measurable e.g. foil-covered insulation, and this aspect is discussed. The various sources of uncertainties are considered and the existing standards and services are also described briefly to place the technique in context.
Although developed on grating instruments, this new measurement capability can be realized on Fourier transform (FT) spectrometers. Progress is being made at NPL in transferring its other MIR measurement capabilities to FT instrumentation. This will safeguard NPL’s future ability to provide these services to customers.
United Kingdom scales for diffuse reflectance in the ultra-violet to near-infrared region are realized at National Physical Laboratory using goniometric techniques, while the mid-infrared scale is based on measurements with a hemisphere reflectometer. Both of these scales have changed recently. In the ultra-violet to near-infrared region this took place on adoption of the goniometrically realized scale which replaced the previous scale traceable to NRC and PTB, while in the mid-infrared the scale change was based on the development of a new direct absolute technique which allowed a re-determination of the diffuse reflectance of BaSO4. Dissemination of the UV/vis/NIR scale will still in the main rely on integrating sphere techniques, and this requires the use of reference standards calibrated using the goniometric technique. The new scale is found to be 0.4 - 0.5 % higher than the previous scale in the visible region, while harmonization with the mid-infrared at 2.5 μm has made good progress, thereby ensuring an independent and continuous scale from the ultra-violet to the far-infrared.
The National Physical Laboratory currently disseminates United Kingdom diffuse reflectance scales from 320 nm to 56 μm. The scale for hemispherical reflectance from 360 nm to 830 nm was previously traceable to the National Research Council of Canada and the Physikalisch-Technische Bundesanstalt, and its extension to 56 μm has relied partly on data published by Morren et al. (1972). Measurements of 0°/45° radiance factor from 360 nm to 830 nm were traceable to the Physikalisch-Technische Bundesanstalt. The National Physical Laboratory now realizes all United Kingdom diffuse reflectance scales independently as described here.
The National Physical Laboratory and the National Research Council of Canada both realize independent scales for regular transmittance in the mid-infrared part of the spectrum. A comparison of these scales has been recently completed. The agreement was excellent, in all cases lying within the quadrature combined uncertainties of the two institutions, and demonstrates the equivalence of the NPL and NRC mid-infrared regular transmittance scales.
The paper describes the high-accuracy radiometric calibration of filter radiometers using both laser and Fourier transform spectrometer based methods to uncertainty levels < 0.1%. The paper also describes the development of detector-based transfer standards and their use for the spectral calibration of radiometric sources. It discusses how these techniques can improve the accuracy and reduce the cost of source calibration.
The design of filters with specific spectral characteristics is a requirement not only for the design of filter radiometers, but also for many applications in optical measurements. The most general type of absorptive filters are composite subtractive-additive filters and the general problem of filter radiometer spectral response optimization using such filters is formulated. The algorithm and software realization of constrained optimization for various objective functions with arbitrary weight functions are described. Successive random search and Hooke-Jeeves methods are employed in the optimization and several goodness-of-fit criteria are used for evaluation of the results. Illustrative numerical examples are presented.
Two Mercury Cadmium Telluride (MCT) detectors have been evaluated for open-path Fourier transform infrared (FT-IR) spectrometry. The first detector was equipped with a standard manufacturers preamplifier; the second detector was equipped with a `linearizing' preamplifier. The two detectors and their respective preamplification systems were evaluated at varied light levels and open-path distances. Chloroform was chosen as an analyte of comparison because it has absorption frequencies at 1220 and 772 cm-1. These two frequencies allow for the visualization of non-linear absorption characteristics. Toluene monitored from a process stack also demonstrates this non-linearity. These data dramatically exhibit the need for a linear detection system in qualitative and quantitative infrared spectrometry.