Advances in entangled-photon sources and single-photon avalanche diodes for quantum technologies in the SWIR
Frank Rutz, T. Passow, Andreas Wörl, Raphael Müller, Quankui K. Yang, Vivienne Leidel, Andreas Bächle, Elke Diwo-Emmer, Jasmin Niemasz, Silvia Giudicatti, Volker Daumer, Robert Rehm
Quantum sensing and quantum communication systems rely on high-performance single- or entangled-photon sources and single-photon detectors enabling experiments based on the quantum nature of single photons. In this contribution, we discuss the development of an entangled-photon source delivering entangled photon pairs with wavelengths of about 1550 nm alongside with single-photon avalanche detectors (SPADs) for the short-wave infrared (SWIR) and for the extended SWIR (eSWIR) spectral range. The fabrication processes of such quantum-enabling technologies is highlighted. The entangled-photon source is based on AlGaAs Bragg-reflection waveguides. Very low difference in effective refractive index of TE and TM polarized photons – important for high polarization entanglement without external compensation – as well as high single and coincidence count rates were achieved. For the fabrication of InGaAs/InP SWIR SPADs, the key technology is the planar process technology via zinc diffusion to produce spatially confined p-type regions. For the zinc-diffusion process, a novel method of selective epitaxial overgrowth was developed, achieving the intended double-well diffusion profile. Experimental data of thus fabricated InGaAs/InP SPADs show the expected dark-current, photo-current, and multiplication-gain characteristics in linear-mode operation as well as breakthrough behavior in Geiger-mode operation at 240 K, which is a typical operating temperature for InGaAs/InP SPADs achievable by thermoelectric cooling. GaSb-based SPADs for the eSWIR are fabricated in a mesa approach showing the expected dark current behavior as well. All three different devices are linked by enabling quantum technologies in the (e)SWIR as well as by using our III/V-semiconductor technology facilities.
Quantum sensing and quantum communication systems rely on high-performance single- or entangled-photon sources and single-photon detectors enabling experiments based on the quantum nature of single photons. In this contribution, we discuss the development of an entangled-photon source delivering entangled photon pairs with wavelengths of about 1550 nm alongside with single-photon avalanche detectors (SPADs) for the short-wave infrared (SWIR) and for the extended SWIR (eSWIR) spectral range. The fabrication processes of such quantum-enabling technologies is highlighted. The entangled-photon source is based on AlGaAs Bragg-reflection waveguides. Very low difference in effective refractive index of TE and TM polarized photons – important for high polarization entanglement without external compensation – as well as high single and coincidence count rates were achieved. For the fabrication of InGaAs/InP SWIR SPADs, the key technology is the planar process technology via zinc diffusion to produce spatially confined p-type regions. For the zinc-diffusion process, a novel method of selective epitaxial overgrowth was developed, achieving the intended double-well diffusion profile. Experimental data of thus fabricated InGaAs/InP SPADs show the expected dark-current, photo-current, and multiplication-gain characteristics in linear-mode operation as well as breakthrough behavior in Geiger-mode operation at 240 K, which is a typical operating temperature for InGaAs/InP SPADs achievable by thermoelectric cooling. GaSb-based SPADs for the eSWIR are fabricated in a mesa approach showing the expected dark current behavior as well. All three different devices are linked by enabling quantum technologies in the (e)SWIR as well as by using our III/V-semiconductor technology facilities.
The implementation and commercialization of quantum cryptography technologies have to face some challenges related to the development of single-photon detectors operating at 1550 nm. The main requirements are: i) high detection efficiency; ii) low noise; iii) high count rate; iv) low timing jitter. Different technologies are currently available for single-photon detection at 1550 nm, but semiconductor devices (like Single-Photon Avalanche Diode, SPAD) offer a photon detection efficiency that is inherently higher than any photocathode employed in vacuum tube detectors. Additionally InGaAs/InP SPADs can detect single photons at 1550 nm with low noise when moderately cooled by means of thermo-electric coolers. Consequently, InGaAs/InP SPAD can be the enabling technology of practical quantum key distribution (QKD) systems, provided that the maximum count rate is increased above 1 Mcps. The main limit is the afterpulsing effect that usually sets too long (< 10 μs) a hold-off time after each avalanche ignition. We present the developments achieved in InGaAs/InP SPAD device design, fabrication technology and front-end electronics, aimed at decreasing the afterpulsing effect, while not impairing photon detection efficiency and timing jitter. The new InGaAs/InP SPADs provide count rates higher than 1 Mcps and temporal response with 60 ps Full-Width at Half Maximum and very short (30 ps time constant) tail. The front-end electronics includes a wide-band pulse generator able to gate the SPAD up to 133 MHz repetition rate. Eventually, a fast avalanche-quenching scheme minimizes quenching time to less than 1 ns, thus effectively reducing afterpulsing by decreasing the total charge flowing through the junction.
Single-photon detectors (SPDs) are the most sensitive instruments for light detection. In the near-infrared range, SPDs based on III–V compound semiconductor avalanche photodiodes have been extensively used during the past two decades for diverse applications due to their advantages in practicality including small size, low cost and easy operation. In the past decade, the rapid developments and increasing demands in quantum information science have served as key drivers to improve the device performance of single-photon avalanche diodes and to invent new avalanche quenching techniques. This Review aims to introduce the technology advances of InGaAs/InP single-photon detector systems in the telecom wavelengths and the relevant quantum communication applications, and particularly to highlight recent emerging techniques such as high-frequency gating at GHz rates and free-running operation using negative-feedback avalanche diodes. Future perspectives of both the devices and quenching techniques are summarized. Recent progress in single-photon detectors for quantum communication based on III–V compound semiconductor avalanche photodiodes is reviewed. Specifically, Jun Zhang and Jian-Wei Pan at the University of Science and Technology of China and their colleagues in the USA and Switzerland introduce technological advances for InGaAs/InP single-photon detector systems in the telecommunication band along with their associated applications in quantum communication. III–V single-photon avalanche diodes are the most practical tools available for detecting ultraweak near-infrared light. The scientists overview important parameters for evaluating the performance of detector systems based on single-photon avalanche diodes and describe the experimental characterization of these parameters. They also consider emerging techniques, including high-frequency gating at gigahertz rates and free-running operation using negative-feedback avalanche diodes. Finally, the future prospects of these devices are considered.
InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage, and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.
Single-photon detectors (SPDs) are the most sensitive instruments for light detection. In the near-infrared range, SPDs based on III–V compound semiconductor avalanche photodiodes have been extensively used during the past two decades for diverse applications due to their advantages in practicality including small size, low cost and easy operation. In the past decade, the rapid developments and increasing demands in quantum information science have served as key drivers to improve the device performance of single-photon avalanche diodes and to invent new avalanche quenching techniques. This Review aims to introduce the technology advances of InGaAs/InP single-photon detector systems in the telecom wavelengths and the relevant quantum communication applications, and particularly to highlight recent emerging techniques such as high-frequency gating at GHz rates and free-running operation using negative-feedback avalanche diodes. Future perspectives of both the devices and quenching techniques are summarized.
Two approaches to single-photon detection at telecom wavelengths have been investigated, using semiconductor and superconductor technologies. The low temperature operation of free-running InGaAs/InP negative feedback avalanche diodes (NFADs) was studied, demonstrating that they can operate with an extremely low dark count rate, which opens up a host of new applications. Secondly, superconducting nanowire single-photon detectors (SNSPDs) based on amorphous materials were developed, fabricated and characterized. These detectors are highly attractive because they can achieve excellent attributes simultaneously, such as high efficiency, low noise, good temporal resolution, no afterpulsing and high count rates. Finally, it was demonstrated that the use of NFADs can enable record distance quantum key distribution (QKD) over 307 km of optical fiber. A next generation QKD system has been proposed and numerically analyzed, aiming at extending the record distance by an additional 100 km and increasing the state-of-the-art secret key rate by over an order of magnitude.
The use of quantum technologies has risen drastically in the last decades, offering an enhancement in terms of the technological capabilities available nowadays. Found in this field of research, quantum communications based on the transmission of single photons offer new approaches to redefine the use of protocols and devices for specialised applications. As a final result, this leads to the accomplishment of long-range quantum networks with terrestrial and satellite-based communications set to establish a new scale of Telecommunication applications. Within these kinds of applications, this project focuses on the assembly of a single-photon detector using a photodiode of type Single-Photon Avalanche Diode (SPAD), essential device to define the level of performance of any quantum communication system. To carry this out, the system is assembled around its centre piece, an Excelitas APD operated in Geiger mode above its breakdown voltage. The electronic circuit that drives the photodiode is characterised to work with its adjusted bias voltage, its dedicated temperature management system and its active quenching circuit to detect pulses with certainty and precision. The final version of the project is adjusted to work in the 1300nm and 1500nm operating wavelengths as the photodiode used is formed by an InGaAs/InP semiconductor structure. Working on top of the original circuit provided initially, the experimental measurements obtained in the course of the project prove that the design modifications implemented have improved the functioning of the whole system. The main achievements accomplished encompass the generation of pulses for photon detection at 20kHz, the reduction of electromagnetic interferences by a factor 40, the enhancement of the manipulated signals in the circuit by a factor of tens, and the correct management of the SPAD temperature to maintain a fixed value of dark counts for a long time.