Light sources for applications in quantum information, quantum-enhanced sensing and quantum metrology are attracting increasing scientific interest. To gain inside into the underlying physical processes of quantum light generation, efficient photon detectors and experimental techniques are required to access the photon statistics. In this work, we employ photon-number-resolving (PNR) detectors based on superconducting transition-edge sensors (TESs) for the metrology of photonic microstructures with semiconductor quantum dots (QDs) as emitters. For the PNR analysis, we developed a state of the art PNR detection system based on fiber-coupled superconducting TESs. Our stand-alone system comprises six tungsten TESs, read out by six 2-stage-SQUID current sensors, and operated in a compact detector unit integrated into an adiabatic demagnetization refrigerator. This PNR detection system enables us to directly access the photon statistics of the light field emitted by our photonic microstructures. In this contribution, we focus on the PNR study of deterministically fabricated quantum light sources emitting single indistinguishable photons as well as twin-photon states. Additionally, we present a PNR-analysis of electrically pumped QD micropillar lasers exhibiting a peculiar bimodal behavior. Employing TESs our work provides direct insight into the complex emission characteristics of QD- based light sources. We anticipate, that TES-based PNR detectors, will be a viable tool for implementations of photonic quantum information processing relying on multi-photon states.
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.
Cr2+-doped chalcogenide crystals have shown to be efficient and broad band tunable solid state lasers for the infrared spectral range between 2μm and 3μm. Pulsed, continuous wave, mode-locked and diode pumped laser operation have been demonstrated in the recent years. Possible application of these mid-infrared lasers include scientific research, remote sensing, trace gas analysis, medicine, biology, materials processing, and ultrashort pulse generation. An overview about the research in the field of lasers based on the tetrahedrally coordinated Cr2+ as active ion will be given. Recent results on the laser characteristics in different host materials will be presented.
A setup for the measurement and calibration of laser power at the excimer laser wavelength of 193 nm was realized. The investigations include the measurements of the damage threshold and the determination of the effective spectral reflectance of the material used for the standard detector, named LM4. The results of these studies allow the complete characterization of the LM4 standard detector including an uncertainty analysis according to the "Guide to the Expression of Uncertainty in Measurement." The LM4 standard detector is linked to the calibration chain established at the Physikalisch-Technische Bundesanstalt (PTB), the German National Metrology Institute. Furthermore, two transfer detectors were linked to the LM4 at the wavelength of 193 nm. Calibrations can be performed down to 193 nm with a relative expanded uncertainty (k = 2) below 1.6 %. Maximum average power, for which calibrations can be performed, is 2.8 W at a repetition rate of 200 Hz. An outlook for the calibration of the laser power at 157 nm is given.
The excitation and emission spectra obtained for Pr3+:YAlO3, Pr3+:LiYF4 and K5PrLi2F10 crystals by means of high-energetic excitation with synchrotron radiation are presented. In the emission spectra broad, overlapping bands in UV range are present. Their positions, bandwidths as well as the short emission decay times suggest, that emission from levels of 4f5d configuration dominate in all of the crystal investigated.
We have grown neodymium doped mixed apatite crystals, (SrxBa1- x)5(PO4)3F, Sr5(P1-xVxO4)3F, and Ba5(P1-xVxO4)3F, and spectroscopically studied them as potential gain media for a laser source for atmospheric water sensing operating at 944.11 nm. We conclude that an appropriate apatite host material for a 944.11 nm laser should be a mixture of Sr5(PO4)3F with a small fraction of Ba5(PO4)3F. The precise wavelength tuning around 944.11 nm can be accomplished by varying the host composition, temperature, and threshold population inversion. In apatite crystals of mixed composition, the amplified spontaneous emission loss at 1.06 micrometers is predicted to be significantly smaller than that in the end members.
Excited state absorption spectra of Cr4+-doped garnets and wurtzite-like crystals were measured between 400 nm and 2000 nm. In Cr4+:Y3Al5O12, a strong polarization dependence of the excited state absorption is observed, while it diminishes for Cr4+:Y3Sc0.5Al4.5O12 and is almost not observed in Cr4+:Y3Sc2Ga3O12. FOr Cr4+:LiAlO2 and Cr4+:LiGaO2 the region of the emission is overlapped by excited state absorption and nonlaser oscillation at room temperature is expected.