Transition edge sensors (TES) are sensitive thermometers that exploit the sharp change in resistance with respect to temperature during the transition between the superconducting and normal metal states. TES sensitivity has led tothe development of calorimeters and bolometers, devices that measure energy or power via a temperature change, that operate at wavelengths from near-IR to X-ray.This thesis documents the design and validation of a hardware signal processor, implemented in a field programmable gate array (FPGA), for Tungsten based TES (W-TES) calorimeters with energy resolution ~0.2 eV. When detecting monochromatic light in the near-IR and visible part of the spectrum (W-TES) calorimeters act as photon number resolving detectors with unrivalled detection efficiency.The processor takes the analogue output pulses arising from calorimeter detections and produces a timestamped stream of event packets containing pulse measurements.The hardware design is motivated by two needs; first, to produce a realtime stream of detection time and photon number estimates for use in quantum optics and information experiments; and secondly to provide a testbed for exploring new strategies and algorithms for estimating the photon energy from a detection pulse.Detection energy is encoded in the shape of the output pulse which changes in different energy regimes. When detecting low energies the pulse linearly scales with energy and as the detection energy increases this scaling becomes non-linear until the sensor eventually saturates. The pulses convey energy information in all the energy regimes but with diminishing resolution. The processor can operate in all regimes by extracting pulses and returning a trace in the event packet.
Transition edge sensors (TES) are sensitive thermometers that exploit the sharp change in resistance with respect to temperature during the transition between the superconducting and normal metal states. TES sensitivity has led tothe development of calorimeters and bolometers, devices that measure energy or power via a temperature change, that operate at wavelengths from near-IR to X-ray.This thesis documents the design and validation of a hardware signal processor, implemented in a field programmable gate array (FPGA), for Tungsten based TES (W-TES) calorimeters with energy resolution ~0.2 eV. When detecting monochromatic light in the near-IR and visible part of the spectrum (W-TES) calorimeters act as photon number resolving detectors with unrivalled detection efficiency.The processor takes the analogue output pulses arising from calorimeter detections and produces a timestamped stream of event packets containing pulse measurements.The hardware design is motivated by two needs; first, to produce a realtime stream of detection time and photon number estimates for use in quantum optics and information experiments; and secondly to provide a testbed for exploring new strategies and algorithms for estimating the photon energy from a detection pulse.Detection energy is encoded in the shape of the output pulse which changes in different energy regimes. When detecting low energies the pulse linearly scales with energy and as the detection energy increases this scaling becomes non-linear until the sensor eventually saturates. The pulses convey energy information in all the energy regimes but with diminishing resolution. The processor can operate in all regimes by extracting pulses and returning a trace in the event packet.
Transition-edge sensors (TES’s) are are extremely sensitive calorimeters able to measure energies of the order of a few electronvolts. They are now well-known in the quantum technology community because of their superb combination of high-efficiency— higher than 95% for photons in the near infrared range [1]—essentially zero dark counts, and photon-number resolution. One of the main challenges when working with TES’s is to extract the photon-number information from the continuous output signal of the detectors. The usual procedure is to accumulate signals over some time—typically ~2 GB per minuite—and then use post-processing techniques to obtain photon-number resolution from the recorded signals [2] Here we introduce an FPGA circuit that analyses TES signals in real-time—recording only specific characteristics such as signal area, height, and length—allowing near realtime photon-number resolution and reducing the memory requirements by orders-of-magnitude. Using this new capability, we are able to optimise the number-resolution of the detector to the range we are interested in for each new experiment. In a preliminary study, we calibrated the TES with a weakly-pulsed 820 nm diode laser, and using just the area data from the FPGA were able to discriminate up to 15 photons. We are able to accurately discriminate an n=2 photon Fock state with parts-per-billion precision, dropping to parts-per-hundred precision at n=15 [3]. It is well known that there are physical limits to the precision with which an image can be formed. There are ways in which this limit can be circumvented, for example using super-resolution techniques that exploit the physical structure of the object, or object illumination with entangled states of light. However, in many applications—for example when the object is very far away—we cannot directly interact with the object, or illuminate it with entangled light: the quantum state of the light field is all that is accessible to the observer. Given a finite size imaging system in the far field—i.e., systems with a finite effective numerical aperture—we show the best way to extract the spatial characteristics of the light source. We implement a general imaging method by measuring the complex degree of coherence using linear optics and our photon-number-resolving detectors. In the absence of collective or entanglement-assisted measurements, our method is optimal over a large range of practically relevant values of the complex degree of coherence [4]. We measure the size and position of a small distant source of pseudo-thermal light, and show that our method outperforms the traditional imaging method by an order of magnitude in precision. Additionally, we show that a lack of photon-number resolution in the detectors has only a modest detrimental effect on measurement precision, further highlighting the practicality of this method as a way to gain significant imaging improvements in a wide range of imaging applications. References [1] A. E. Lita, A. J. Miller, and S. W. Nam, Optics Express 16, 3032 (2008). [2] G. Brida, et al., New Journal of Physics 14, 085001, (2012). [3] L. Assis, et al., preprint (2020) [4] L. A. Howard, et al., Physical Review Letters 123, 143604 (2019).
Superconducting transition-edge sensors (TES) are extremely sensitive microcalorimeters used as photon detectors with unparalleled energy resolution. They have found application from measuring astronomical spectra through to determining the quantum property of photon-number, n ^ = a ^ † a ^ , for energies from 0.6-2.33eV. However, achieving optimal energy resolution requires considerable data acquisition – on the order of 1GB/min – followed by post-processing, which does not allow access to energy information in real time. Here we use a custom hardware processor to process TES pulses while new detections are still being registered, allowing photon-number to be measured in real time as well as reducing data requirements by orders-of-magnitude. We resolve photon number up to n = 16 – achieving up to parts-per-billion discrimination for low photon numbers on the fly – providing transformational capacity for applications of TES detectors from astronomy through to quantum technology.
A transition edge sensor (TES) is one of superconducting photon detectors, which has a photon number resolving ability in light pulses. The TES device is a kind of calorimeters operated at an extremely low temperature, and the energy of the photons is measured as a resistance change in a superconducting transition region of the TES. The advantages of the TESs are an excellent energy resolution and a high quantum efficiency. However a response speed is limited due to slow thermal recovery time. To overcome this, we fabricated new TES devices which are based on a titanium superconductor. The critical temperature of our titanium films is around 410 mK, which greatly improves the thermal recovery time. The observed decay time constant of response signals to the light pulses is around several hundreds of ns, that make it possible to operate the devices at a counting rate over 1 MHz. The photon number resolving power is 0.35 eV(FWHM) for a 5 μm size device even at the high operating temperature. The system quantum efficiency is 65 % by embedding the TES films in an optical structure with a high reflection dielectric mirror and an anti-reflection coatings fabricated by an ion beam assisted sputtering method. These features are very promising for high speed photon number resolving applications in the quantum information field.
Transition-Edge Sensors (TESs) are microcalorimeters that measure the energy of incident single photons by the resistance increase of a superconducting film biased within the superconducting-to-normal transition. TES are able to detect single photons from IR to X-ray with an intrinsic energy resolution and photon-number discrimination capability. Metrology, astronomy and quantum \ncommunication are the fields where these properties can be particularly useful. In this work, we report about characterization of different TESs based on Ti films. Single photons have been detected from 200nm to 800 nm working at transition temperature Tc ∼ 100 mK. Using a pulsed laser at 690nm we have demonstrated the capability to resolve up to five photons.
SQUIDs can be used as amplifiers for superconducting Transition Edge Sensor (TES) photon counting detectors. According to the physical process of photon counting, a TES signal simulator was developed to evaluate the performance of SQUID amplifier for TES detectors. A triangle simulation signal was determined to be a close match to that from a real TES photon counter. The dynamic range for the output voltage versus bias current was first characterized and then the current signals were incrementally coupled to circuit to determine the highest sensitivity of a series-array SQUID amplifier. The sensitivities are obtained by changing the triangle signal amplitude added to the TES signal simulator. The impedance changes can be deduced and further obtain the temperature changes of TES devices. When knowing the photon energy, TES design parameters can be known according to the thermal characteristics. In conclusion, the TES simulator can be well applied to guide the device design for effective readout.
Photon-number resolving transition-edge sensors (TESs) with near unity system detection efficiency enable novel approaches to quantum computing, for example, heralding robust Gottesman–Kitaev–Preskill qubit states. Increasing the speed of the detectors increases the rate at which these states can be heralded. In addition, depending on the details of the scheme, faster detectors can reduce the complexities of the hardware implementation. In previous work, we demonstrated that adding a small amount of gold between the tungsten film and silicon substrate can increase thermal conductance and reduce detector recovery time. In that study, the readout electronics imposed limitations on stable biasing conditions of the TES detector, and the TES could only be biased at higher than ideal values. In this report, we demonstrate the operation of the TES illuminated by a heavily attenuated pulsed laser running at 1 MHz repetition rate and examine the limits to adding gold to speed up device recovery times using a higher bandwidth readout system. The best performance was achieved by combining a 15×15μm2 tungsten TES with 5μm3 of gold, which resulted in a recovery time faster than 250 ns, with an energy resolution of 0.25 eV full-width at half maximum at 0.8 eV photon energy.