Ronny Stolz

• Dr.
• Head of Department at Leibniz Institute of Photonic Technology

We report on the design and implementation of adiabatic quantum flux parametron (AQFP) buffer gates utilizing cross-type Nb/AlOx/Nb Josephson junctions with IC of 20 μA, designed to operate at mK temperatures. We, therefore, discuss design considerations, circuit simulation and optimization and their technological implementation. The preliminary re...

We present an approach allowing an optically pumped magnetometer (OPM) to be operated within the Earth’s magnetic field as a vector magnetometer, the sensitive axis of which can be freely defined. This approach enables the measurement of any vector component of the Earth’s magnetic field with the same sensitivity. The OPM is realized by a microfabr...

We've developed a scalable microwave SQUID multiplexer (μMUX) readout architecture adapted for arrays of transition edge sensors (TESs) to be exploited in a THz security camera. The camera system combines a scanning optics together with a 128-pixel TES array and aims for security gate operations with a stand-off detection distance of up to 25 m. Th...

We present a novel approach allowing an optically pumped magnetometer (OPM) to be operated within Earth's magnetic field as a vector magnetometer whose sensitive axis can be freely defined. This approach enables the measurement of any vector component of the Earth's magnetic field with the same sensitivity. The OPM is realized by a microfabricated...

Controllable coupling between the odd and even fundamental modes of an asymmetric half-wavelength superconducting coplanar waveguide resonator is demonstrated. The resonant frequency of the even mode Ωe could be tuned by an external magnetic field, while the resonant frequency of the odd mode Ωo is field independent. To realize the tunability of Ωe...

Noise in superconducting quantum interference devices (dc SQUIDs) with different design, based on Nb/AlOx/Nb technology, has been systematically measured at temperature T = 4.2 K. We demonstrate that for all our devices the power spectral density of the white noise (above a frequency of about 1 kHz) is determined by the shunt resistors, reaching ab...

The Cryogenic Current Comparator (CCC) for beamlines is designed for the non-destructive, highly sensitive, and absolute measurement of bunched (AC) and un-bunched (DC) beam current of charged particle in the nA range using the external magnetic field of the beam. Niobium based CCCs are running at the CERN-Antiproton Decelerator (beamline diameter...

Quantum computers represent a prominent example of technology harnessing quantum phenomena for practical applications. Implementations based on superconducting solid-state qubits play a leading role. These have facilitated the implementation of the first commercially viable quantum computers through the use of well-established and scalable fabricat...

Josephson tunnel junctions represent a key element in superconducting electronics and quantum circuits. For many years, shadow evaporation by means of Dolan-type bridges has been the state-of-the-art for deep sub- micrometer sized structures. Increasing demand in the number of Josephson junctions, e.g. in qubit circuits and travelling wave parametr...

Fluxonics Newsletter - A SPECIAL EDITION ABOUT SUPERCONDUCTOR QUANTUM ELECTRONICS FOUNDRY

Quantum sensing provides advanced technologies which significantly improve sensitivity and accuracy for sensing changes of motion, gravity, electric and magnetic field. Therein, quantum sensors for the detection of magnetic fields, so-called quantum magnetometers, are one of the most promising technological realizations. We firstly will provide a b...

Measurements of weak magnetic fields demand a small distance between the sensor and the to-be-measured object. Optically pumped magnetometers (OPMs) utilize laser light and the Zeeman effect in alkali vapor cells to measure those fields. OPMs can be used in transmission or reflection geometry. A minimization of the distance between active volume an...

In mobile applications such as geomagnetic surveying, two major effects hamper the use of optically pumped magnetometers: dead zones, sensor orientations where the sensors signal amplitude drops; and heading errors, a dependence of the measured magnetic field value on the sensor orientation. We present a concept for an omnidirectional magnetometer...

In mobile applications such as geomagnetic surveying, two major effects hamper the use of optically pumped magnetometers: dead zones, sensor orientations where the sensors signal amplitude drops; and heading errors, a dependence of the measured magnetic field value on the sensor orientation. We present a concept for an omnidirectional magnetometer...

The operating principle of traveling-wave parametric amplifiers is typically understood in terms of the standard coupled mode theory, which describes the evolution of forward propagating waves without any reflections, i.e., for perfect impedance matching. However, in practice, superconducting microwave amplifiers are unmatched nonlinear finite-leng...

The high kinetic inductance of niobium nitride (NbN) thin films can be used for an implementation of compact on-chip inductances in cryoelectronic circuits. Here, for the first time, we demonstrate the implementation of a hybrid superconducting technology that includes the fabrication of standard aluminum submicron Josephson junctions and the NbN a...

The performance of superconducting electronic devices such as superconducting quantum bits (qubits) and superconducting quantum interference devices (SQUIDs) strongly relies on high-quality Josephson junctions (JJ) and their integration into surrounding circuit elements. Therefore, a corresponding fabrication technology should allow for the fabrica...

In this work, advanced methods and processing schemes for the analysis of data from a Superconducting Gravimeter (SG) will be introduced and their relevance on acquired data proved. The SG CD-034 was installed on Easter of 1999 in the Geodynamic Observatory Moxa of the Friedrich Schiller University Jena, Germany. Initially, the quality of the recor...

This paper studies the impact of mechanical deformations on the performance of a coaxial-type cryogenic current comparator (CCC). Such deformations may become a concern as the size of the CCC increases ( e.g. when used as a diagnostic device in a particle accelerator facility involving beamlines with a large diameter). In addition to static deform...

This paper presents a new shield configuration for cryogenic current comparators (CCCs), namely the folded coaxial geometry. An analytical model describing its shielding performance is first developed, and then validated by means of finite element simulations. Thanks to this model, the fundamental properties of the new shield are highlighted. Addit...

This paper studies the impact of mechanical deformations on the performance of a coaxial-type cryogenic current comparator (CCC). Such deformations may become a concern as the size of the CCC increases (e.g. when used as a diagnostic device in a particle accelerator facility involving beamlines with a large diameter). In addition to static deformat...

Research on quantum sensors for the detection of magnetic fields (quantum magnetometers) is one of the fast-moving areas of Quantum Technologies. Since there exist expectations about their use in geophysics, this work will provide a brief overview on the various developing quantum technologies and their individual state of the art for implementing...

Gradient measurement of the magnetic field vector, especially full-tensor magnetic gradiometers (FTMGs), provides various advantages over gradient components derived from measurements of the total magnetic intensity (TMI). These advantages include higher spatial resolution, directional information, and thus more detailed anomaly delineation and a s...

Traveling wave parametric amplifiers based on kinetic or Josephson nonlinear inductance are known to be microwave quantum limited amplifiers. Usually, a perfectly impedance-matched model is used to describe their characteristics in terms of standard coupled mode theory. In practice, the amplifiers are unmatched nonlinear devices with finite length,...

We present a portable optically pumped magnetometer instrument for ultrasensitive measurements within the Earth’s magnetic field. The central part of the system is a sensor head operating a MEMS-based Cs vapor cell in the light-shift dispersed Mz mode. It is connected to a compact, battery-driven electronics module by a flexible cable. We briefly r...

Wetland environments, with their excellent conservation conditions, provide geoarchaeological archives of past human activities. However, the subsurface soil is difficult to access due to high groundwater tables, unstable sediments, and the high cost of excavation. In this study, we present a ground-based non- and minimal-invasive prospection conce...

Waveguides with superconducting Josephson junction-based metamaterial are widely used as parametric amplifiers. However, the precise estimation of power entering the device is crucial for the estimation of gain and noise temperature. This is nontrivial when the measurement tract is not symmetrical. We present a basic framework for the analysis of p...

Moisture stored in near surface soils is a key feature for a manifold of ecological processes. The soil, being the interface between the atmosphere and the lithosphere, plays a crucial role for the transport of water and the dissolved substances therein. At present, there are no suitable direct methods to determine soil moisture content at the requ...

Carrier mobilities and concentrations were measured for different p- and n-type silicon materials in the temperature range 0.3–300 K. Simulations show that experimentally determined carrier mobilities are best described in this temperature range by Klaassen’s model. Freeze-out reduces the carrier concentration with decreasing temperature. Freeze-ou...

We report on the development of magnetic background field-tolerant superconducting quantum interference filter (SQIF) based on low-capacitance sub-micrometer sized cross-type Josephson junctions either as current sensing amplifiers—even on chip—for advanced superconducting quantum interference device (SQUID) readout circuits or as magnetic field se...

Non-destructive measurements of nA beam currents in particle beam storage rings with a Cryogenic Current Comparator (CCC) are well established. The detection of beam currents with small amplitudes with a CCC in a storage ring demands a high slew rate which is caused by the rapid change of the beam current exceeding the operational limit of the SQUI...

More than 50 years ago superconducting quantum interference devices (SQUIDs) were invented. Since then many applications opened up. Already in a 1980 workshop (Weinstock and Overton 1981 SQUID Applications to Geophysics (Society of Exploration Geophysicists)) the application of SQUIDs in geosciences was reviewed. The fabrication and cooling technol...

Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP's magnetic moments is measured by sensiti...

There is a cleardemand to increase detection depths in the context of raw materialexploration programs. Semi-airborne electromagnetic (semi-AEM) methodscan adress these demands by combining the advantages of powerful transmitters deployed on the ground with efficienthelicopter-borne mapping of the magnetic field response in the air.The penetration...

Fetal magnetocardiograms are highly sensitive to interferences in unshielded environments, the measurements being realized indirectly. We aimed at removing repetitive deterministic interferences, applying the Wiener filter in the wavelet domain. An effective compression of data is performed using the Walsh-Hadamard Transform. Real fetal data has be...

We present a portable optically pumped magnetometer instrument for ultra-sensitive measurements within the Earth's magnetic field. The central part of the system is a sensor head operating a MEMS-based Cs vapor cell in the light-shift dispersed Mz mode. It is connected to a compact, battery-driven electronics module by a flexible cable. We briefly...

Bias lines routed over a ground plane naturally form microstrip lines associated with the presence of a capacitance. This can lead to unwanted resonances when coupled to Josephson junctions. This work presents an electrical model of a shunted Josephson junction with its bias lines and pads, fabricated with the 1 kA/cm $^2$ RSFQ niobium process of...

In this paper, we present new integrated on-chip planar-type superconducting quantum interference device (SQUID) first order gradiometers, which are manufactured by a new mix and match fabrication technology combining sub-μm sized Josephson junctions (JJs) with cm-scale pickup loops. The fabrication technology is described and the design is schemat...

Oberflächen-NMR ist ein etabliertes Verfahren der angewandten Hydrogeophysik zur hydrogeologischen Charakterisierung des Untergrundes bis in maximal 150m Tiefe. Mit Hilfe von Präpolarisations-Spulen, welche das messbare NMR-Signal in Abhängigkeit von der verwendeten Stromstärke um mehr als eine Größenordnung erhöhen können, ist der Einsatz von Ober...

We experimentally investigate the influence of the orientation of optically pumped magnetometers in Earth’s magnetic field. We focus our analysis to an operational mode that promises femtotesla field resolutions at such field strengths. For this so-called light-shift dispersed Mz (LSD-Mz) regime, we focus on the key parameters defining its performa...

Bias lines routed over a ground plane naturally form microstrip lines associated with the presence of a capacitance. This can lead to unwanted resonances when coupled to Josephson junctions. This work presents an electrical model of a shunted Josephson junction with its bias lines and pads, fabricated with the 1 kA/cm$^2$ RSFQ niobium process of th...

We demonstrate and characterize superconducting nanowire single-photon detectors made from atomic layer-deposited (ALD) NbN layers. To assess the suitability of these films as a detector material, transport properties of bare films and bridges of different dimensions and thicknesses are investigated. Similar ratios of the measured critical current...

We experimentally investigate the influence of the orientation of optically pumped magnetometers in Earth's magnetic field. We focus our analysis to an operational mode that promises femtotesla field resolu-tions at such field strengths. For this so-called light-shift dispersed Mz(LSD-Mz) regime, we focus on the key parameters defining its performa...

We report results of our development of two types of microwave amplifiers based on Superconducting quantum interference devices (SQUIDs) for CAPP (Center for Axion and Precision Physics Research) axion search experiments. The first amplifier, Microstrip SQUID Amplifier (MSA) has a wide bandwidth. Power dissipation in resistive shunts results in a d...

We demonstrate and characterize first superconducting nanowire single-photon detectors (SNSPDs) made from atomic layer-deposited (ALD) NbN layers. To assess the suitability of these films as a detector material, transport properties of bare films and bridges of different dimensions and thicknesses are investigated. Similar ratios of the measured cr...

This paper presents a new shield configuration for cryogenic current comparators (CCCs), namely the folded coaxial geometry. An analytical model describing its shielding performance is first developed, and then validated by means of finite element simulations. Thanks to this model, the fundamental properties of the new shield are highlighted. Addit...

Purpose The purpose of this paper is to present a simulation study using a model of a new optically pumped magnetometer sensor for application in the field of magnetoencephalography. The effects of sensor distance and orientation on the measurement information and the sensitivity to neuronal sources are investigated. Further, this paper uses a comb...

Measurements of the magnetic field are one of the most used methods in geophysical exploration. In order to reduce the degree of ambiguity of this technique during inversion and modelling, data acquired by newly available gradiometer systems based on Superconducting Quantum Interference Devices (SQUIDs) are used. These systems provide measurements...

When optically pumped magnetometers are aimed for use in the Earth's magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement results. Measurement errors and inaccuracies related to the heading of the sensor can be an even more severe problem in the case of special operational con...

For the first time a mobile underwater full tensor magnetic gradiometer (FTMG) system based on low-Tc superconducting quantum interference devices (SQUIDs) has been deployed in order to scan the sea floor for magnetized targets. The application is mainly focused on waste deposits and unexploded ordnance (UXO), but could also include shallow geologi...

We report on a novel concept and prototype development of a coreless SQUID-based charged-particle beam monitor as a non-destructive diagnostic tool for accelerator facilities. Omitting the typically used pickup coil with a high magnetic permeability core leads to a significant improvement in low-frequency noise performance. Moreover, a revised shie...

When optical pumped magnetometers are aimed for the use in Earth's magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement result. Inaccuracy in relation to the heading of the sensor can be an even severe problem in the case of special operational configurations, such as for exam...

Transient electromagnetics (TEM) is a well-established method for mineral, groundwater, and geothermal exploration. Supercon- ducting quantum interference device (SQUID)-based magnetic- field receivers used for TEM have quantitative advantages and higher sensitivity compared with commonly used induction coils. Special applications are deep sounding...

In ovo research is a valuable option of preclinical research, but imaging studies are severely limited by the costs of dedicated equipment needed for small-size eggs. We sought to verify the feasibility of using larger eggs of ostrich (Struthio camelus) for the imaging with PET/CT scanners used for routine clinical investigations. Methods: Ostrich...

We report results about an optimized three-dimensional nanoSQUID based on niobium tunnel nanojunctions having the loop suspended to reduce the parasitic capacitance. The SQUID loop has a size of 400 × 600 nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> while the dimension of the square tunne...

For ground-based electromagnetic methods in geophysics dc superconducting quantum interference devices based on high-temperature superconductors are well suited as magnetic field sensors. Therefore, we introduce in this paper an advanced fabrication technology for high-temperature superconducting dc SQUIDs based on step-edge Josephson junctions. Th...

The new version of a Cryogenic Current Comparator with eXtended Dimensions (CCC-XD) for the beam monitoring of charged particles which is currently in the optimization cycle is presented herein. The CCC-XD is designed for a non-destructive, highly sensitive monitoring of a few nA beam intensities for 150 mm beamline diameters at the Facility for An...

In the experiments for dark-matter QCD-axion searches, very weak microwave signals from a low-temperature High-Q resonant cavity should be detected using the highest sensitivity. The best commercial low-noise cryogenic semiconductor amplifiers based on high electron mobility transistors have a lowest noise temperature above 1.0 K, even if they are...

The effect of flux trapping on the flux-voltage characteristics of multi-loop SQUID magnetometers was investigated by means of repeated cool-down cycles in a stepwise increased magnetic background field. For a SQUID with N parallel loops, N different flux offsets, each separated by Φ 0 / N , were observed even in zero magnetic field. These flux off...

The most precise current existing gravimeters for continuous observation of the Earth’s gravity field are the superconducting gravimeters (SG) of the company GWR in California (USA), for the measurement of deflection of a levitated superconducting test mass. These instruments allow the high resolution recording and study in detail of long period si...

Cardiac problems lead to significant health risks for nowadays' society. Newly developed technologies, such as recording of the magnetic heart signal (magnetocardiograms), enable the passive monitoring of the heart activity. Still, the method is subjected to high amplitude magnetic interferences and reliable signal processing algorithms have to be...

In 2013, large scale magnetic prospection was carried out in Franconia, Germany, to reveal remains of a canal construction and corresponding infrastructure built by order of Charlemagne in the Early Middle Ages. The extended canal structures of the so-called Fossa Carolina were expected within a part of the main European watershed between Altmühl a...

Direct Current Superconducting QUantum Interference Devices (dc SQUIDs) are sensors for the detection of magnetic flux or any physical quantity that can be transformed into magnetic flux. They consist of a superconducting loop interrupted by two resistively shunted Josephson tunnel junctions. Typically operated at 4.2 K, they exhibit magnetic flux...

In this work, a new design for an optically pumped magnetic field camera (MC) is proposed which will be used to measure bio-magnetic fields. The MC is intended to be used as a non-invasive and absolute measuring tool in the neuroscientific research on epileptic activity and/or to monitor drug delivery in small animals. Therefore, the MC has to be a...

We report the performance of a reliable three-dimensional nanometer-sized Superconducting QUantum Interference Device (SQUID). The use of superconductor-isolator-superconductor Nb/Al-AlOx/Nb Josephson tunnel junctions together with small SQUID loop dimensions permits a high modulation depth of the SQUID's critical current and thus leads to very low...

Technological processes for the fabrication of low-and high-Tc Josephson junctions, aimed for certain applications, are described. On the one hand, the integration of low-Tc superconductor digital electronics with superconducting sensor arrays enables input signal processing with quantum limited resolution at millikelvin temperatures. We describe t...

We report on the development of a new family of SQUID current sensors based on sub-micron cross-type Josephson tunnel junctions. Their low total junction capacitance permit high usable voltage swings of more than 100 {\mu}V and exceptional low noise of the SQUIDs at 4.2 K. Integrated rf-filter as well as high tolerable background fields during cool...

We report on the development of a new family of superconducting quantum interference device (SQUID) current sensors based on sub-micron cross-type Josephson tunnel junctions. Their low total junction capacitance permits high usable voltage swings of more than 100 μV and exceptional low noise of the SQUIDs at 4.2 K. Integrated rf-filters as well as...

We report on the development of an ultralow noise thin-film based SQUID magnetometer. A niobium thin-film pickup coil is connected to the input coil of a SQUID current sensor. The low capacitance of the used sub-micrometer cross-type Josephson junctions enable superior noise performance of the device. Application scenarios e.g. in geophysics and ul...

We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlOx/Nb Josephson junctions offer large $I_CR_N$-products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 {\mu}m exhibit white flux n...

Fabrication of devices composed of Josephson junctions in trilayer technology is usually compromised by the topography of the subjacent layers. If the structures of subsequent layers traverse steps, several adverse effects arise. Lithography may be impaired because of issues with resist thickness uniformity and focus depth, and the superconducting...

We present an optically pumped magnetometer working in a new operational mode—the light-shift dispersed Mz (LSD-Mz) mode. It is realized combining various features; (1) high power off-resonant optical pumping; (2) Mz configuration, where pumping light and magnetic field of interest are oriented parallel to each other; (3) use of small alkali metal...

Commonly, geomagnetic prospection is performed via scalar magnetometers that measure values of the total magnetic intensity. Recent developments of superconducting quantum interference devices have led to their integration in full tensor magnetic gradiometry systems consisting of planar‐type first‐order gradiometers and magnetometers fabricated in...

We propose a novel high performance radiation detector and imaging sensor by a ground-breaking core-shell diode array design. This novel core-shell diode array are expected to have superior performance respect to ultrahigh radiation hardness, high sensitivity, low power consumption, fast signal response and high spatial resolution simultaneously. T...

We report on the absolute calibration of a three-axis SQUID-cascade vector magnetometer suited for mobile operation in the Earth's magnetic field. It is based on low temperature superconductor (LTS) dc SQUIDs with sub-micrometer sized cross-type Josephson junctions and exhibits a white noise level of about 10 fT Hz−1/2. Due to the cascaded operatio...

We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlOx/Nb Josephson junctions offer large ICRN-products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 μm exhibit white flux noise lev...

The paper studies the influence of biorthogonal wavelets upon several steps of the processing of magnetocardiograms recorded in stress conditions: baseline drift correction, denoising, and compression. The implementation of a novel technique implies the performance of several tests in order to define the optimal parameters of the algorithms. Theref...

We report on the development of an ultralow-noise thin-film-based superconducting quantum interference device (SQUID) magnetometer. A niobium thin-film pickup coil is connected to the input coil of a SQUID current sensor. The low capacitance of the used submicrometer cross-type Josephson junctions enables superior noise performance of the device. A...

We present a detailed experimental and theoretical study on the relaxation of spin coherence due to the spin-exchange mechanism arising in the electronic ground states of alkali-metal vapor atoms. As opposed to the well-explored formation of a stretched state in a longitudinal geometry (magnetic field parallel to the laser propagation direction) we...

An on-chip magnetic shielding technique was characterized on several DC-SQUIDs to prepare the next generation of complex digital RSFQ circuits designed by the FLUXONICS foundry. The maximal frequency of operation of a toggle flip-flop cell was used as a criteria to validate the concept. It goes from a simulated value of 52 GHz (46 2 GHz experimenta...

The article contains sections titled: • Introduction • Laboratory Instruments • Geomagnetics • Electromagnetic Methods • Gravimetry • Future Impact of SQUID in Geophysics

We discuss the theoretical development of the measurement of the component from a surface nuclear magnetic resonance (SNMR) experiment using superconducting quantum interference devices (SQUIDS) as a point B-field receiver. We discuss the differences between point receivers compared to traditional coincident-loop receivers, and demonstrate the firs...

Papers presented at the 2nd Bilateral Indo-Italian Workshop NEEM 2015 Rome, Italy October 12-14, 2015 Organized with the support of the Directorate General for the Country Promotion Ministry of Foreign Affairs and International Cooperation by Consorzio Hypatia Department of Science & Technology of India IMEM-CNR Institute for Plasma Research (Ghand...

We report on the development of a three-axis absolute vector magnetometer suited for mobile operation in the Earth's magnetic field. It is based on low critical temperature dc superconducting quantum interference devices (LTS dc SQUIDs) with sub-micrometer sized cross-type Josephson junctions and exhibits a white noise level of about 10 fT/Hz1/2. T...

The Josephson comparator is one of the building blocks of superconductor electronics. It is used as a decision element in all analog and digital circuits. For fast high-bandwidth analog-to-digital converters as well as for digital circuits with reduced switching energy its high sensitivity is most important. Thermal noise limits its decision uncert...

The aim of this work is to deploy a new SQUID (Superconducting Quantum interference device) based instrument for the measurement of the full magnetic gradient tensor of the Earth’s magnetic field in survey scenarios in a sedimentary basin in Thuringia, a local province in Germany. This task requires developing according processing, inversion, and i...