Superconducting nanowires are widely used in quantum computing, superconducting electronics, and low-temperature physics due to their high sensitivity, compact footprint, and low noise. Here, we present a gate-tunable superconducting nanowire thermometer that enables high-precision temperature measurements in the liquid-helium regime by applying a gate voltage. Experimental results demonstrate stable operation in the 2.5-6.2 K range, with a maximum sensitivity of 4.51×105 cps/K, indicating the potential for sub-millikelvin resolution. The device further exhibits a minimum noise-equivalent temperature difference (NETD) of 5.5 mK, corresponding to millikelvin-level measurement accuracy. Its on-chip integrability, fast response, and tunable performance make it a promising solution for low-temperature sensing and on-chip thermal monitoring in quantum chips. This work provides an experimental platform and theoretical basis for electric-field-controlled superconducting electronics and highlights the potential of gate-controlled nanowires for integrated cryogenic sensing technologies.
Superconducting nanowires are widely used in quantum computing, superconducting electronics, and low-temperature physics due to their high sensitivity, compact footprint, and low noise. Here, we present a gate-tunable superconducting nanowire thermometer that enables high-precision temperature measurements in the liquid-helium regime by applying a gate voltage. Experimental results demonstrate stable operation in the 2.5-6.2 K range, with a maximum sensitivity of 4.51×105 cps/K, indicating the potential for sub-millikelvin resolution. The device further exhibits a minimum noise-equivalent temperature difference (NETD) of 5.5 mK, corresponding to millikelvin-level measurement accuracy. Its on-chip integrability, fast response, and tunable performance make it a promising solution for low-temperature sensing and on-chip thermal monitoring in quantum chips. This work provides an experimental platform and theoretical basis for electric-field-controlled superconducting electronics and highlights the potential of gate-controlled nanowires for integrated cryogenic sensing technologies.
Cryogenic systems are essential to many modern scientific and technological applications, including MRI superconducting magnets, particle accelerators, astrophysical detectors and quantum computing platforms, all of which operate at temperatures well below 120 K. In this framework, accurate temperature monitoring is, therefore, critical. However, conventional Resistance Temperature Detectors (RTDs) suffer from significant limitations in cryogenic environments, such as wiring complexity, power dissipation, limited low-temperature operation and large footprint, which restrict their integration in increasingly complex cryogenic infrastructures. Superconducting devices offer a promising alternative due to their high sensitivity at low temperatures, low power dissipation and compatibility with integrated quantum technologies. Inspired by Microwave Kinetic Inductance Detectors (MKIDs), this work investigates superconducting microwave resonators as minimally invasive, frequency-multiplexed cryogenic thermometers operating below 12 K. In particular, strategies to tune and enhance temperature sensitivity are explored by studying the effects of the superconducting thin-film thickness and surface nanostructuring. The first part of the study examines NbTi(N) planar resonators with thicknesses ranging from 20 nm to 150 nm, where temperature sensing is based on the temperature dependence of the kinetic inductance. S-shaped split-ring resonators resonating near 1.1 GHz are inductively coupled to a coplanar transmission line and characterized under cryogenic conditions. A clear trade-off between temperature sensitivity and quality factor is observed: thinner films achieve higher sensitivity, up to approximately 19 MHz/K for 20 nm thick devices, while the quality factor, typically exceeding 10^4, is found to degrade when the thickness is reduced. This trade-off leads to an optimal temperature resolution, with sub-microkelvin noise-equivalent temperature (NET) values. In particular, a minimum NET of (0.53±0.09) µK/Hz^(1/2) at 4.2 K is achieved for a 100 nm thick resonator, which is also exploited to study low-frequency temperature fluctuations in liquid helium. In the second part, a possible approach to enhance the temperature sensitivity, through surface nanostructuring, is investigated. Arrays of nanogaps are patterned in high-current regions of a 1.3 GHz resonator, in order to locally suppress superconductivity, reduce the critical temperature of the film and, therefore, accentuate the slope of the temperature-sensitive curve. These weak-links are realized by partially etching a 100 nm NbTi film, to leave 20-30 nm thick remaining nanogaps. Measurements reveal a significant increase in temperature sensitivity, reaching values as high as up to (62±1) MHz/K, which correspond to one order-of-magnitude improvement over non-nanostructured devices. Although this enhancement comes with increased noise-equivalent temperature, the results demonstrate the feasibility of engineering superconducting weak links to improve RF cryogenic thermometry and provide a solid foundation for future optimization. In reason of the achieved results, such an approach could find successful applications for a sub-µK high-resolution cryogenic temperature monitoring, specifically for integrated quantum architectures, further benefiting from the frequency-multiplexing that naturally arises from the multiple allocation of different superconducting microwave resonators.
Thousands to millions of sensitive signals will need to be conveyed through all the temperature stages of a dilution fridge to operate future large-scale quantum processors made of many quantum bits. The exploding number of heat-conductive coaxial cables will overwhelm the fridge cooling capabilities, detrimental to the quantum core. Moving the control electronics down to cryogenic temperatures allows the use of already-available superconducting cables, alleviating heat conduction between low-temperature stages, and appears as a clear path towards scalability in the number of operating qubits.This Ph.D. work aimed to explore the use of the industrial CMOS 28nm Fully-Depleted Silicon-On-Insulator (FD-SOI) technology at cryogenic temperatures for quantum computing applications. Our first objective is to extend the sparse existing knowledge about the FD-SOI 28nm transistors at cryogenic temperatures for practical aspects of circuit design and later for developments of compact models.To speed-up the characterization of single devices with the inherent hour-long cooling cycles, we designed an integrated circuit multiplexing a thousand of transistors for different geometries and gate-stack flavors for low-frequency measurement of the current-voltage characteristics and pair-matching analysis from 300 down to 0.1K. We discuss and analyze the evolution trends with varying geometry at different temperatures for important quantities in circuit design, such as the transconductance, the conductance, and the transconductance over drain current ratio of individual transistors.Secondly, we explore the low-temperature co-integration and the full on-chip integration of semiconductor quantum devices with classical electronics aimed at specific measurements down to the millikelvin range.We first focus on the sub-nanoampere current measurement of quantum dot devices by designing and characterizing a low-power transimpedance amplifier (TIA). The high-gain amplifier is successfully applied to measure the current across single- and double quantum-dot devices, respectively wire-bonded a few mm away or on-chip integrated a few micrometers-away. To further leverage the integration into the same substrate, we connected GHz-range voltage-controlled oscillators to one of the gates of the double dot in an attempt to observe discrete charge pumping in a fully-integrated device.Lastly, we tackled the measurement of the gate capacitance of single quantum devices by proposing a new measurement scheme making use of the cryogenic electronics capabilities as an alternative to the well-known reflectometry. By integrating a voltage-controlled current excitation and a voltage-sensing amplifier in the 200 MHz range, both in close proximity to the quantum device connected to an LC tank, the read-out circuitry of a variation in the device capacitance becomes a purely lumped-element system with impedance measurement of the resonant circuit without any wave propagation like in reflectometry. This approach increases simplicity and compactness of the measurement set-up. We even replace the bulky passive inductor used in reflectometry by an active inductor made of transistors and capacitors, offering improved scalability with a 3-orders of magnitude lower area for the same inductance. The resulting circuit successfully measured aF-capacitance variations of nanometric transistors at 4.2K revealing oscillatory quantum effects in the gate capacitance as a function of the gate and back-gate voltages.At the end of this dissertation, a picture is given with the challenges laying ahead related to circuit architecture and design for the ultimate goal of entering into the era of large-scale quantum processing.
Abstract Many classic and quantum devices need to operate at cryogenic temperatures, demanding advanced cryogenic digital electronics for processing the input and output signals on a chip to extend their scalability and performance. Here, we report a superconducting binary encoder with ultralow power dissipation and ultracompact size. We introduce a multigate superconducting nanowire cryotron (nTron) that functions as an 8-input OR gate within a footprint of approximately 0.5 μm2. Four cryotrons compose a 4-bit encoder that has a bias margin of 18.9%, an operation speed greater than 250 MHz, an average switching jitter of 75 ps, and a power dissipation of less than 1 μW. We apply this encoder to read out a superconducting-nanowire single-photon detector array whose pixel location is digitized into a 4-bit binary address. The small size of the nanowire combined with the low power dissipation makes nTrons promising for future monolithic integration.
We present a superconducting microresonator thermometer based on two-level systems (TLSs), which is drop-in compatible with cryogenic microwave systems. The operational temperature range is 50–1000 mK (which may be extended to 5 mK), and the sensitivity (50–75 μK/Hz) is relatively uniform across this range. The miniature footprint that conveniently attaches to the feedline of a cryogenic microwave device facilitates the measurement of on-chip device temperature and requires no additional thermometry wiring or readout electronics. We demonstrate the practical use of these TLS thermometers to investigate static and transient chip heating in a kinetic inductance traveling-wave parametric amplifier operated with a strong pump tone. TLS thermometry may find broad application in cryogenic microwave devices such as superconducting qubits and detectors.
Single-photon coincidence counters are essential components in integrated quantum photonics, enabling efficient logic discrimination and real-time error correction at the chip level. However, monolithic integration at cryogenic temperature remains challenging. Here, we demonstrate a coincidence counter based on superconducting nanowire cryotrons (nTron). The circuit comprises five nTron devices, including delay gates, buffer gates, and an AND gate, achieving a maximum bias margin of 22% at a bit error rate (BER) of 10−5. Operating at 1 MHz, the counter exhibits a static power consumption of 282 nW and a dynamic power consumption of approximately 2 nW at a maximum operation frequency of 17 MHz. The coincidence time window is tunable, with a minimum width below 1 ns, and its position can be adjusted via bias currents. This design offers compatibility with superconducting nanowire single-photon detectors in fabrication and operation, supporting monolithic integration for scalable quantum photonic systems.
We discuss the design and development of a cryogenic set-up down to ~1.8 K for carrying out measurements on superconducting nanowire single-photon detectors.The set-up consists of two separate low-temperature inserts, one for electrical characterization and the other for optical measurements and characterization of single-photon detectors.A sample holder with necessary arrangements for precise alignment of laser light with the active area of the device to enhance optical coupling efficiency has been designed for the optical probe.The invar alloy has been used for the sample holder to ensure that the alignment is not disturbed at low temperature.Single-mode fibres due to their high transmission rate, minimum attenuation and least distortion have been used to shine light on the samples.The sample holder with 20-pin LCC socket and matching chip carrier provides convenient and fast sample mounting in the electrical insert.Mumetal has been employed to cover the sample space in both the inserts in order to attenuate any electromagnetic interference.Temperature stability with the passage of time has been monitored.It has been found that variation in temperature is less than 10 mK at the lowest operating temperature.Another important advantage of the system is its low enough liquid helium loss rate (~100 ml/h) with all inserts, which allows uninterrupted measurements for several days without any refilling of liquid helium.