arXiv subjects

Giorgio De Simoni

Publications and source records attributed to Giorgio De Simoni.

At least 19 recordsLinked to original sources

arXiv2026

A Voltage-Controlled Josephson Frequency Comb

Microwave frequency combs constitute promising resources for quantum technologies, cryogenic electronics, and multiplexed sensing architectures. In this work, we propose a frequency-comb generator based on a Josephson field-effect transistor operated in a relaxation-oscillation regime. The device comprises a gate-tunable ballistic superconductor-semiconductor-superconductor junction embedded in a resistively shunted circuit, in which electrostatic control of the carrier density enables in situ tuning of both the critical current and the Josephson inductance. Time-domain circuit simulations indicate that the resulting oscillator produces coherent voltage pulses whose Fourier spectrum forms a microwave frequency comb. In contrast to conventional Josephson-based comb architectures, the proposed platform provides direct electrical control of the comb spacing, emission frequencies, and modal power distribution via a gate electrode. For a representative Al/InAs implementation, we demonstrate continuous frequency coverage in the technologically relevant 1-10 GHz range. Furthermore, the concept is shown to be compatible with higher-$T_c$ superconductors, underscoring its potential as a compact and scalable microwave source for cryogenic quantum information and sensing applications.

cond-mat.supr-con↗

arXiv2026

A Zero-Bias Superconducting Voltage Amplifier Based on the Bipolar Thermoelectric Effect

We introduce a zero-bias superconducting voltage amplifier that harvests energy from a thermal gradient by exploiting negative differential resistance (NDR) in an asymmetric tunnel junction. The device is based on an asymmetric superconductor-insulator-superconductor (SIS) junction with an energy-gap ratio of $\Delta_1/\Delta_2 = 0.5$, connected in series with a load resistor. Owing to the superconducting bipolar thermoelectric effect, the current-voltage characteristic of the junction exhibits a region of NDR, in which the net current flows opposite to the applied voltage. This mechanism enables voltage amplification in the absence of any external electrical bias, relying solely on the temperature difference between the electrodes ($T_H \simeq 1$ K, $T_B \simeq 20$ mK). Numerical simulations predict a voltage gain of 20 dB, a 1 dB compression point at an input amplitude of 2 $\mu$V, and a total harmonic distortion below $-50$ dB. The input-referred noise is approximately 1 nV/$\sqrt{Hz}$, with an associated thermal load on the order of nanowatts. The frequency response is broadband from near DC, with a $-3$ dB cutoff around 180 MHz, set by the RC time constant of the junction. Using Al-, Al-Cu-, and AlO$_x$-based technologies, the amplifier is compatible with conventional superconducting circuit fabrication processes. These findings demonstrate that thermoelectric superconducting junctions can deliver bias-free voltage amplification from near DC up to about 200 MHz, making them promising candidates for transition-edge sensor readout, quantum circuit instrumentation, and low-frequency cryogenic signal processing.

cond-mat.supr-con↗

arXiv2026

Extremely weak electron-phonon coupling in Josephson junctions built on InAs on Insulator

InAs-on-Insulator (InAsOI) enables an effective superconducting proximity effect and extremely weak electron-phonon (e-ph) coupling, allowing precise electronic-temperature control with minimal power. Using Josephson junction thermometry, we extract sub-Kelvin e-ph coupling parameters, confirming strong thermal decoupling and robust superconducting performance. The combination of weak e-ph interaction and full electrostatic tunability makes InAsOI a powerful platform for coherent caloritronics, ultrasensitive bolometry, single-photon detection, and gate-controlled superconducting thermal circuits.

cond-mat.supr-con↗

arXiv2026

Highly-linear flux-to-voltage transducer based on superconducting quantum interference proximity transistors

Superconducting quantum interference devices (SQUIDs) are state-of-the-art in ultra-sensitive magnetometry; however, conventional SQUID devices are fundamentally limited by the inherently nonlinear and periodic nature of their transfer function. Although flux-locked loop (FLL) configurations can mitigate this issue, they introduce electronic complexity and bandwidth constraints that hinder scalability in quantum circuits. In this work, we present an experimental demonstration of the bi-SQUIPT, a flux transducer that modulates the density of states in a proximitized superconducting weak link. The device employs a dual-loop architecture with differential readout, which enables cancellation of non-linearities typical of individual elements, achieving a voltage swing of approximately 120 $\mu$V. Measurements yield a spurious-free dynamic range (SFDR) of up to 60 dB, consistent with theoretical predictions and comparable to that of SQUID arrays, while maintaining power dissipation in the femtowatt range. The results further highlight a remarkable operational stability up to 600 mK, positioning the bi-SQUIPT as an enabling technology for high-density cryogenic quantum electronics.

cond-mat.supr-con↗

arXiv2025

Giant thermal modulation via a semiconductor-superconductor photonic field-effect heat transistor

We present a groundbreaking demonstration of thermal modulation in a field-effect-controllable semiconductor-superconductor hybrid structure, wherein the heating mechanism is exclusively radiative. The architecture comprises two reservoirs separated by $\sim 1$ mm and interconnected via a completely non-galvanic electrical circuit, enabling the transfer of black-body radiation from the hot to the cold reservoir. Our device utilizes a superconducting Josephson field-effect transistor to achieve magnetic-field-free gate-tunable regulation of heat currents within the circuit. While prior studies have indicated the potential for electrostatic modulation of thermal transport properties, our framework demonstrates a temperature modulation of up to $\sim 45$ mK, exceeding prior findings by more than an order of magnitude. Furthermore, it proves a thermal transimpedance of $\sim 20$ mK/V at a bath temperature of $30$ mK. The development of such systems holds substantial promise for advancing heat management and routing in quantum chips and radiation sensors, as it enables precise nonlocal control of heat flow towards a designated structure, even when the heat source is distant and non-galvanically coupled.

cond-mat.mes-hall↗

arXiv2025

Quantum Bipolar Thermoelectricity

Thermoelectricity is generally understood as a classical effect emerging from energy-dependent transport asymmetries. Here we uncover a purely quantum mechanism, where a superconducting S-I-S' tunnel junction in thermal equilibrium develops a nonlinear bipolar thermoelectric response owing to the dynamical Coulomb blockade and the emission-absorption imbalance of a cold electromagnetic bath. Two representative environments are analysed, revealing Seebeck coefficients up to 100 $\mu$V/K for realistic junction parameters. Because the response directly reflects the spectral properties of the surrounding environment, our results suggest that bipolar quantum thermoelectricity could provide a new route for spectroscopic sensing of electromagnetic modes and for designing low-temperature thermoelectric devices with environmentally engineered performance.

cond-mat.mes-hall↗

arXiv2025

Streamline controlled rectification of supercurrent in thin-film asymmetric weak links

In this study, we examined the supercurrent diode effect (SDE) in mesoscopic superconducting weak links formed by asymmetric Dayem bridges. These planar metallic constrictions, which naturally exhibit Josephsonlike behavior, offer a fundamental platform for investigating nonreciprocal transport phenomena in a regime where the bridge width aligns with the superconducting coherence length. The foundational concept is inspired by the Tesla valve, a classical fluidic device that achieves flow rectification through interference and turbulence between fluid streams enabled by geometric asymmetry. Analogously, we demonstrate that spatial asymmetry within superconducting structures can result in rectification due to the polarity-dependent interaction between transport and screening currents. By implementing controlled geometric defects at the junction between the constriction and superconducting leads, we induce current crowding and disrupt spatial inversion symmetry, thus facilitating directional switching behavior. Experimental results indicate a linear-in-field rectification regime at low magnetic fields, driven by the interaction between transport and screening currents, which is succeeded by complex vortex dynamics within the superconducting banks at elevated fields. Time-dependent Ginzburg-Landau simulations replicate significant features of the experimental observations and substantiate the influence of both screening currents and rearrangements of Abrikosov vortices. A comparative study across various geometries highlights the crucial role of defect shape and spatial confinement in determining the rectification efficiency, revealing a minimum threshold in bridge width below which crowding-induced SDE is significantly reduced. Our findings advocate for mesoscopic Dayem bridges as a flexible platform for designing and controlling superconducting diode functionalities.

cond-mat.supr-con↗

arXiv2025

The Ferroelectric Superconducting Field Effect Transistor

The ferroelectric field-effect transistor (Fe-FET) is a three-terminal semiconducting device first introduced in the 1950s. Despite its potential, a significant boost in Fe-FET research occurred about ten years ago with the discovery of ferroelectricity in hafnium oxide. This material has been incorporated into electronic processes since the mid-2000s. Here, we observed ferroelectricity in a superconducting Josephson FET (Fe-JoFET) operating at cryogenic temperatures below 1 Kelvin. The Fe-JoFET was fabricated on the InAsOI platform, which features an InAs epilayer hosted by an electrical insulating substrate, using HfO2 as the gate insulator, making it a promising candidate due to its ferroelectric properties. The Fe-JoFET exhibits significant hysteresis in the switching current and normal-state resistance transfer characteristics, which depend on the range of gate voltages. This phenomenon opens a new research area exploring the interaction between ferroelectricity and superconductivity in hybrid superconducting-semiconducting systems, with potential applications in cryogenic data storage and computation. Supporting this, the Fe-JoFET was operated as a cryogenic superconducting single memory cell, exhibiting both dissipative and non-dissipative states. Its non-volatility was tested over a 24-hour measurement period. We also demonstrated that the Fe-JoFET can retain information at temperatures above the superconductor critical temperature, resulting in a temperature-fault-tolerant memory cell resistant to temperature oscillations or, in the worst case, cryostat faults.

cond-mat.supr-con↗

arXiv2025

A Thermally Modulated SINIS Trasconductance Amplifier

We introduce a superconducting transconductance amplifier based on the thermal modulation of a SINIS (Superconductor-Insulator-Normal metal-Insulator-Superconductor) configuration. The device is composed of a normal metal island interfaced with two superconducting leads through tunnel barriers, establishing a voltage-biased symmetric SINIS setup. An additional NIS junction connects the island to a third superconducting lead, which serves as input. When the input voltage surpasses the superconducting gap, the resultant injection of quasiparticles increases the electronic temperature of the island, thereby modulating the SINIS current. We perform numerical analyzes of the device performance, influenced by input voltage, frequency, and bath temperature. At bath temperatures below 250 mK, the device shows a transconductance exceeding 4 mS and a current gain exceeding 45 dB. Both gain and transconductance maintain their levels up to 1 MHz, but decrease at higher frequencies, with a -3 dB cutoff around 10 MHz, and an average power dissipation of approximately 5 nW. Our simulations reveal a fully voltage-controlled, three-terminal superconducting amplifier characterized by high transconductance and gain, achieved through thermally mediated signal transduction. This architectural design presents a promising avenue for cryogenic amplification with reduced power dissipation and compatibility with current superconducting electronic systems.

cond-mat.supr-con↗

arXiv2025

Photonic heat amplifiers based on a disordered semiconductor

A photonic heat amplifier (PHA) designed for cryogenic operations is introduced and analyzed. This device comprises two variable-range-hopping reservoirs connected by lossless lines, which allow them to exchange heat through photonic modes. This configuration enables negative differential thermal conductance (NDTC), which can be harnessed to amplify thermal signals. To achieve this, one reservoir is maintained at a high temperature, serving as the source terminal of a thermal transistor. Concurrently, in the other one, we establish tunnel contacts to metallic reservoirs, which function as the gate and drain terminals. With this arrangement, it is possible to control the heat flux exchange between the source and drain by adjusting the gate temperature. We present two different parameter choices that yield different performances: the first emphasizes modulating the source-drain heat current, while the second focuses on the modulation of the colder temperature variable range hopping reservoir. Lastly, we present a potential design variation in which all electronic reservoirs are thermally connected through only photonic modes, allowing interactions between distant elements. The proposal of the PHA addresses the lack of thermal transistors and amplifiers in the mK range while being compatible with the rich toolbox of circuit quantum electrodynamics. It can be adapted to various applications, including sensing and developing thermal circuits and control devices at sub-Kelvin temperatures, which are relevant to quantum technologies.

cond-mat.mes-hall↗

arXiv2024

Josephson Field Effect Transistors with InAs on Insulator and High Permittivity Gate Dielectrics

InAs on Insulator (InAsOI) has been recently demonstrated as a promising platform to develop hybrid semiconducting-superconducting Josephson Junctions (JJs) and Josephson Field Effect Transistors (JoFETs). The InAsOI consists of an InAs epilayer grown onto a cryogenic-electrically-insulating InAlAs metamorphic buffer, which allows the electrical decoupling of surface-exposed adjacent devices together with a high critical current density integration. The miniaturization of Si microchips has progressed significantly due to the integration of high permittivity (high-k) gate insulators, allowing an increased gate coupling with the transistor channel with consequent reduced gate operating voltages and leakages. As well as for Si-based FETs, integrating high-k gate insulators with JoFETs promises similar advantages in superconducting electronics. Here, we investigate the gate-tunable electrical properties of InAsOI-based JoFETs featuring different high-k gate insulators, namely, HfO2 and Al2O3. We found that both the ungated and gate-tunable electrical properties of the JoFETs are strongly dependent on the insulator chosen. With both dielectrics, the JoFETs can entirely suppress the switching current and increase the normal state resistance by 10-20 times using negative gate voltages. The HfO2-JoFETs exhibit improved gate-tunable electrical performance compared to those achieved with Al2O3-JoFETs, which is related to the higher permittivity of the insulator. Gate-dependent electrical properties of InAsOI-based JoFETs were evaluated in the temperature range from 50 mK to 1 K. Moreover, under the influence of an out-of-plane magnetic field, JoFETs exhibited an unconventional Fraunhofer diffraction pattern, from which an edge-peaked supercurrent density distribution was calculated.

cond-mat.supr-con↗

arXiv2024

Supercurrent Time Division Multiplexing with Solid-State Integrated Hybrid Superconducting Electronics

Time-division multiplexing of cryogenic signals is a promising approach to reduce space requirements, shorten cooldown times, and increase the number of quantum devices measured per cooldown. We demonstrate time-division multiplexing of non-dissipative supercurrents using voltage-controlled hybrid superconducting demultiplexers. These chips integrate superconducting Josephson Field Effect Transistors including Al superconducting electrodes, proximitized semiconducting InAs channels, and hafnium oxide gate insulators. Each transistor fully suppresses the switching current and increases the resistance 20 times under a gate voltage of -4.5 V. A demultiplexer with one input and eight outputs showed a non-dissipative input range of +-2 uA, operating up to 100 MHz in signal frequency and 100 kHz in switching frequency at 50 mK. It achieved near-zero insertion loss in the superconducting state and an ON/OFF ratio of 17.5 dB. By optimizing the signal layout, the operation was extended up to 4 GHz using a demultiplexer with two outputs.

cond-mat.supr-con↗

arXiv2024

A quasiparticle-injection superconducting microwave relaxation oscillator

We propose a superconducting microwave relaxation oscillator based on a nanowire shunted by a resistor and an inductor controlled by quasiparticle injection from a tunnel junction positioned on it: the QUISTRON. This device exhibits relaxation oscillator behavior with DC voltage-controlled frequency tuning and DC current bias. The device frequency is modulated via the tunnel junction, which induces localized heating by injecting quasiparticles. This heating mechanism modulates the nanowire switching current, enabling relaxation oscillations when it falls below the bias current. We demonstrate the device operating principles and characterize its performance across various parameters, including different choices of shunt resistor, shunt inductance, and bath temperature ranging from 20 mK to 1 K. The device showed oscillation with a frequency range approximately between 1 GHz and 10 GHz and total energy dissipation per cycle of $\sim100$ zJ. Our results suggest that this design offers a promising platform for compact, tunable superconducting oscillators in the microwave spectrum with potential applications in quantum information processing, microwave technology, and ultra-low-power electronics. The straightforward frequency control mechanism and integration potential make this device an attractive candidate for superconducting microwave local oscillators.

cond-mat.mes-hall↗

arXiv2024

Cryogenic Behavior of High-Permittivity Gate Dielectrics: The Impact of the Atomic Layer Deposition Temperature and the Lithographic Patterning Method

Dielectrics featuring a high relative permittivity, i.e., high-k dielectrics, have become the standard insulators in gate architectures, enhancing the electrical performance of both room temperature and cryogenic electronics. This study delves into the cryogenic (3 K) performance of high-k dielectrics commonly used as gate insulators. We fabricated Al2O3 and HfO2 layers via Atomic Layer Deposition (ALD) and we extrapolated relative permittivity (k) and dielectric strength (E_BD) from AC (100 Hz to 100 kHz) and DC measurements on metal-insulator-metal capacitors. Our findings reveal a strong dependence of HfO2 cryogenic performance on the ALD growth temperature, while the latter shows a negligible impact on Al2O3. We estimated a ~9 % and ~14 % reduction of the relative permittivity of HfO2 and Al2O3, respectively, from 300 K to 3 K. Additionally, we designed and fabricated Al2O3/HfO2 bilayers and we checked their properties at cryogenic temperatures. The study also investigates the impact of the patterning method, namely, UV or electron-beam lithography (acceleration voltage of 10, 20, or 30 kV), on the high-k dielectric properties.

cond-mat.mtrl-sci↗

arXiv2024

Extremely weak sub-kelvin electron-phonon coupling in InAs On Insulator

We are proposing, as an ideal candidate for caloritronic devices operating at subKelvin temperatures, a hybrid superconductor-semiconductor platform named InAs on insulator (InAsOI). This heterostructure is made by doped InAs grown on an insulating buffer of InAlAs on a GaAs substrate. Caloritronic devices aim to heat or cool electrons out of equilibrium with respect to the phonon degree of freedom. However, their performances are usually limited by the strength of the electron-phonon (e-ph) coupling and the associated power loss. Our work discusses the advantages of the InAsOI platform, which are based on the significantly low e-ph coupling measured compared to all-metallic state-of-the-art caloritronic devices. Our structure demonstrates values of the e-ph coupling constant up to two orders of magnitude smaller than typical values in metallic structures.

cond-mat.supr-con↗

arXiv2024

InAs on Insulator: A New Platform for Cryogenic Hybrid Superconducting Electronics

Superconducting circuits based on hybrid InAs Josephson Junctions (JJs) play a starring role in the design of fast and ultra-low power consumption solid-state quantum electronics and exploring novel physical phenomena. Conventionally, 3D substrates, 2D quantum wells (QWs), and 1D nanowires (NWs) made of InAs are employed to create superconducting circuits with hybrid JJs. Each platform has its advantages and disadvantages. Here, we proposed the InAs-on-insulator (InAsOI) as a groundbreaking platform for developing superconducting electronics. An epilayer of semiconducting InAs with different electron densities was grown onto an InAlAs metamorphic buffer layer, efficiently used as a cryogenic insulator to decouple adjacent devices electrically. JJs with various lengths and widths were fabricated employing Al as a superconductor and InAs with different electron densities. We achieved a switching current density of 7.3 uA/um, a critical voltage of 50-to-80 uV, and a critical temperature equal to that of the superconductor used. For all the JJs, the switching current follows a characteristic Fraunhofer pattern with an out-of-plane magnetic field. These achievements enable the use of InAsOI to design and fabricate surface-exposed Josephson Field Effect Transistors with high critical current densities and superior gating properties.

cond-mat.supr-con↗

arXiv2024

Quasi-ideal feedback-loop supercurrent diode

We suggest using a device called the Bootstrap Superconducting Quantum Interference Device (BS-SQUID) to break the reciprocity in charge transport. This device uses magnetic flux back-action to create a nonreciprocal current-voltage characteristic, which results in a supercurrent rectification coefficient of up to approximately 95\%. The BS-SQUID works as a quasi-ideal supercurrent diode (SD) and maintains its efficiency up to about 40\% of its critical temperature. The external magnetic flux can be used to adjust or reverse the rectification polarity. Finally, we discuss the finite-voltage operation regime of the SD and present a possible application of our device as a half- and full-wave signal rectifier in the microwave regime.

cond-mat.supr-con↗

arXiv2023

Gate-controlled supercurrent effect in dry-etched Dayem bridges of non-centrosymmetric niobium rhenium

The application of a gate voltage to control the superconducting current flowing through a nanoscale superconducting constriction, named as gate-controlled supercurrent (GCS), has raised great interest for fundamental and technological reasons. To gain a deeper understanding of this effect and develop superconducting technologies based on it, the material and physical parameters crucial for GCS must be identified. Top-down fabrication protocols should be also optimized to increase device scalability, although studies suggest that top-down fabricated devices are more resilient to show GCS. Here, we investigate gated superconducting nanobridges made with a top-down fabrication process from thin films of the non-centrosymmetric superconductor NbRe. Unlike other devices previously reported, our NbRe devices systematically exhibit GCS, when made in specific conditions, which paves the way for higher device scalability. Our results also suggest that surface properties of NbRe nanobridges and their modification during fabrication are key for GCS.

cond-mat.supr-con↗