Recent experimental demonstration of the quantum coherent phase slip and current quantization in the superconductors, the fundamental phenomena dual to the coherent Cooper pair tunneling and voltage quantization (Shapiro steps), enables the development of a new quantum device, the Bloch transistor (BT). BT has a unique functionality: it can deliver quantized non-dissipative current to the quantum circuit. BT consists of two coupled Josephson Junctions (JJ) in the regime of coherent quantum phase slip. At the heart of the BT operation is a new mechanism for phase-locking the Bloch oscillations in JJs to microwaves via induced charge. The charge phase locking allows not only quantization of current but also gate voltage control of this quantization through the Aharonov-Casher effect. We study the operation of the BT and analyze its parameters. BT technology is scalable and compatible with other superconducting quantum devices, making it part of an emerging cryogenic quantum technology platform.

Theory predicts the superconductor-to-insulator transition (SIT) to emerge from the competition between Anderson localization, which tends to localize single-particle wavefunctions, and superconductivity, which establishes long-range correlations in the superconducting order parameter. In two-dimensional (2D) superconducting films, the transition temperature T_c at which resistance vanishes, R_(T_BKT)=0, is set by the Berezinskii-Kosterlitz-Thouless (BKT) mechanism and satisfies T_BKT< T_c0, where T_c0 is the mean-field transition temperature. In weakly disordered samples T_BKT≲ T_c0, whereas increasing disorder drives T_BKT≪ T_c0 near the SIT. Whether the finite-temperature transition retains its BKT character throughout this crossover remains an open question. Here, we investigate the evolution of both sheet resistance R_(T) and superfluid stiffness J_s(T) over a wide range of disorder strength W. We establish that even near the SIT, the finite-temperature transition from the superconducting to the resistive state remains of BKT type. However, as disorder approaches the critical value, the zero temperature superfluid phase stiffness, J_s(0), is found to vanish rapidly while T_c0 remains finite, which we attribute to quantum phase fluctuations as the drive for the zero-temperature transition. Three decades after its experimental discovery by Haviland, Liu, and Goldman, our measurements clarify the origin of the SIT in 2D films.

We report on observation of two coherent quantum phenomena, the current quantization in theJosephson Junction (JJ) and the Aharonov-Cashier effect. The synergy of two effects is seen as the phase locking of the JJ with the oscillating charge engaged by the microwaves (the current quantization), and a control of the phase locking phenomenon with the static charge of the gate electrode (the Aharonov-Cashier effect). The experimental system consists of two coupled JJs in the regime of coherent quantum phase slip. When the microwave is applied, the quantized current plateaus appear on the I - V curve. The effect is dual to the Shapiro voltage steps in JJs. We modulate the quantized current with the static charge induced by the gate electrode. Conceptually, the system has the functionality of the Bloch Transistor: it can deliver gate-controlled quantized non-dissipative current to the quantum circuit.

The quantum Josephson voltage standard is well established across the metrology community for many years. It relies on the synchronisation of the flux tunneling in the S/I/S Josepson junctions (JJ) with the microwave radiation (MW). The phenomenon is called the Shapiro steps. Together with the Quantum Hall resistance standard, the voltage standard forms the foundation of electrostatic metrology. The current is then defined as the ratio of the voltage and resistance. Realisation of the quantum current standard, would close the electrostatic metrological triangle of voltage-resistance-current. The current quantisation, the inverse Shapiro steps, was recently shown using the superconducting nanowires and small JJ. The effect is a synchronization of the MW with the Cooper pair tunnelling. This paves the way to combine the JJ voltage and current standards on the same chip and demonstrate feasibility of the multi-standard operation. We show the voltage and current quantization on the same chip up to frequency of 10 GHz, corresponding to the amplitudes 0.021 mV and 3.23 nA respectively. The accuracy of the voltage and current quantisation, however, is relatively low, 35 ppk and 100 ppk respectively. We discuss measures to optimise the JJs, circuit and environment to boost the amplitude and accuracy of the standards.

We present a comprehensive investigation of the Berezinskii-Kosterlitz-Thouless transition in ultrathin strongly disordered NbN films. Measurements of resistance, current-voltage characteristics, and kinetic inductance on the very same device reveal a consistent picture of a sharp unbinding transition of vortex-antivortex pairs that fit standard renormalization group theory without extra assumptions in terms of inhomogeneity. Our experiments demonstrate that the previously observed broadening of the transition is not an intrinsic feature of strongly disordered superconductors and provide a clean starting point for the study of dynamical effects at the Berezinskii-Kosterlitz-Thouless transition.

This article presents the oldest iron smelting furnaces of the Xiongnu Empire period in central Mongolia and argues that a significant smelting center existed at the site of Baga Nariĭn Am. Five iron smelting furnaces and four smelting installations were excavated, with a total 26 furnaces further identified through SQUID magnetometry. In combination with a review of data on iron production in contemporary Mongolia, the Transbaikal region, Tuva, the Minusinsk Basin and the Altai, we argue that this new data alters existing narratives of the adoption of iron in eastern Eurasia. While iron smelting as such was adopted from the Minusinsk Basin, where the oldest iron smelting furnaces in eastern Eurasia are currently found, we suggest that the driving force behind the massive boom in iron metallurgy from the second century BCE onward was the Xiongnu Empire. During the course of the Xiongnu Empire, the development of more efficient iron technology is evident, with the steppe empire also inventing a new furnace type. These findings are significant for understanding the dynamics of iron industries in the eastern Eurasian Steppe and paves the way for necessary work on metallurgical installations in the Minusinsk Basin and Tuva.

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 and magnetized source calls for reflection geometry with integrated mirrors. Unfortunately, cesium reacts chemically with most materials, especially high-performing materials, such as gold. Herein, we show the first functional OPM cell using a gold mirror inside the cell. We fabricated the gold mirrors with and without a passivation layer in order to evaluate the feasibility of expanding on the limited list of possible mirror materials. A comparison of this implementation revealed that mirrors without a passivation layer only reach a reflectivity of about 6% while mirrors with a passivation layer retain reflectivity values of about 90% in the visible light to near-infrared spectrum. This result and the proof of elemental cesium in the alkali vapor cell demonstrates the feasibility of passivated gold mirrors for applications in alkali vapor cells for OPMs.

Cities in the Eurasian steppes, a core of nomadic empires, are rare. Erecting a city from scratch is even less typical. However, Khar Khul Khaany Balgas, situated north of the Khangai Mountains in central Mongolia, is such an exceptional example, never built over by subsequent settlements. Overlooked until now because researchers dated its latest settlement phase into the 17th century a.d., the first radiocarbon dates and material culture prove its existence during the Mongol empire only. During the past years, we conducted comprehensive geophysical and topographic mapping of the site, as well as a pedestrian survey, including its hinterland, and excavated a kiln. The layout of the city resembles that of the capital, Karakorum. Both cities together reveal that the Mongol Khans had a specific idea about the organization of a city. They were dependent on Chinese craftsmen to erect the buildings but not on Chinese city planning and ideology.

The AC Josephson effect predicted in 1962 and observed experimentally in 1963 as quantised voltage steps (the Shapiro steps) from photon assisted tunnelling of Cooper pairs is among the most fundamental phenomena of quantum mechanics and is vital for metrological quantum voltage standards. The physically dual effect, the AC coherent quantum phase slip (CQPS), photon assisted tunnelling of magnetic fluxes through a superconducting nanowire, is envisaged to reveal itself as quantised current steps. The basic physical significance of the AC CQPS is also complemented by practical importance in future current standards; a missing element for closing the Quantum Metrology Triangle. In 2012, the CQPS was demonstrated as superposition of magnetic flux quanta in superconducting nanowires. However the direct sharp current steps in superconductors; the only unavailable basic effect of superconductivity to date, was unattainable due to lack of appropriate materials and challenges in circuit engineering. Here we report the direct observation of the dual Shapiro steps in a superconducting nanowire. The sharp steps are clear up to 26 GHz frequency with current values 8.3 nA and limited by the present setup bandwidth. The current steps have been theoretically predicted in small Josephson junctions (JJs) 30 years ago. However, broadening unavoidable in JJs prevents their direct experimental observation. We solve this problem by placing a thin NbN nanowire in an inductive environment.

Superconducting niobium nitride (NbN) films with nominal thicknesses of 4 nm, 5 nm, 7 nm, and 9 nm were grown on sapphire substrates using atomic layer deposition (ALD). We observed probed Hall resistance (HR) (Rxy) in external out-of-plane magnetic fields up to 6 T and magnetoresistance (MR) (Rxx) in external in-plane and out-of-plane magnetic fields up to 6 T on NbN thin films in Van der Pauw geometry. We also observed that positive MR dominated. Our study focused on the analysis of interaction and localisation effects on electronic disorder in NbN in the normal state in temperatures that ranged from 50 K down to the superconducting transition temperature. By modelling the temperature and magnetic field dependence of the MR data, we extracted the temperature-dependent Coulomb interaction constants, spin–orbit scattering lengths, localisation lengths, and valley degeneracy factors. The MR model allowed us to distinguish between interaction effects (positive MR) and localisation effects (negative MR) for in-plane and out-of-plane magnetic fields. We showed that anisotropic dephasing scattering due to lattice non-idealities in NbN could be neglected in the ALD-grown NbN thin films.

In the thirteenth century AD, the city of Karakorum was founded as the capital of the Mongol Empire. Relatively little archaeological attention, however, has been directed at the site and the phenomenon of steppe urbanism. The authors report new magnetic and topographic surveys of the walled city and the surrounding landscape. The resulting maps reveal the city in unprecedented detail. Combining the magnetic and topographical data with aerial photographs, pedestrian surveys and documentary sources reveals the extent, layout and organisation of this extensive settlement. Road networks and areas of variable occupation density and types of activities deepen our understanding of this important commercial hub and royal palace, which is conceptualised as a form of 'implanted' urbanism.

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 concept adapted to the conditions of wetlands. We investigated the Fossa Carolina in South Germany, a canal that was intended in 792/793 AD by Charlemagne to bridge the Central European Watershed. Although the resulting Carolingian banks and the fairway with wooden revetments are very imposing, archaeological traces of off-site construction activities have not been identified hitherto. Based on a geophysically surveyed intensive linear magnetic anomaly parallel to the Carolingian canal, we aimed to prove potential off-site traces of Carolingian construction activities. In this context, we built up a high-resolution cross-section using highly depth-accurate direct push sensing and ground-truthing. Our results showed the exact geometry of the canal and the former banks. Thus, the magnetic mass anomaly could be clearly located between the buried organic-rich topsoil and the Carolingian banks. The thermoluminescence dating showed that the position of the magnetic mass anomaly reflected Carolingian activities during the construction phases, specifically due to heat exposure. Moreover, we found hints of the groundwater supply to the 5-metre wide navigable fairway.

Superconducting niobium nitride thin films are used for a variety of photon detectors, quantum devices, and superconducting electronics. Most of these applications require highly uniform films, for instance, when moving from single-pixel detectors to arrays with a large active area. Plasma-enhanced atomic layer deposition (ALD) of superconducting niobium nitride is a feasible option to produce high-quality, conformal thin films and has been demonstrated as a film deposition method to fabricate superconducting nanowire single-photon detectors before. Here, we explore the property spread of ALD-NbN across a 6-in. wafer area. Over the equivalent area of a 2-in. wafer, we measure a maximum deviation of 1% in critical temperature and 12% in switching current. Toward larger areas, structural characterizations indicate that changes in the crystal structure seem to be the limiting factor rather than film composition or impurities. The results show that ALD is suited to fabricate NbN thin films as a material for large-area detector arrays and for new detector designs and devices requiring uniform superconducting thin films with precise thickness control.

ABSTRACTSediment budgeting concepts serve as quantification tools to decipher the erosion and accumulation processes within a catchment and help to understand these relocation processes through time. While sediment budgets are widely used in geomorphological catchment‐based studies, such quantification approaches are rarely applied in geoarchaeological studies. The case of Charlemagne's summit canal (also known as Fossa Carolina) and its erosional collapse provides an example for which we can use this geomorphological concept and understand the abandonment of the Carolingian construction site. The Fossa Carolina is one of the largest hydro‐engineering projects in Medieval Europe. It is situated in Southern Franconia (48.9876°N, 10.9267°E; Bavaria, southern Germany) between the Altmühl and Swabian Rezat rivers. It should have bridged the Central European watershed and connected the Rhine–Main and Danube river systems. According to our dendrochronological analyses and historical sources, the excavation and construction of the Carolingian canal took place in AD 792 and 793. Contemporary written sources describe an intense backfill of excavated sediment in autumn AD 793. This short‐term erosion event has been proposed as the principal reason for the collapse and abandonment of the hydro‐engineering project. We use subsurface data (drillings, archaeological excavations, and direct‐push sensing) and geospatial data (a LiDAR digital terrain model (DTM), a pre‐modern DTM, and a 3D model of the Fossa Carolina] for the identification and sediment budgeting of the backfills. Dendrochronological findings and radiocarbon ages of macro remains within the backfills give clear evidence for the erosional collapse of the canal project during or directly after the construction period. Moreover, our quantification approach allows the detection of the major sedimentary collapse zone. The exceedance of the manpower tipping point may have caused the abandonment of the entire construction site. The spatial distribution of the dendrochronological results indicates a north–south direction of the early medieval construction progress. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

In autumn 793, Charlemagne visited the fossatum magnum (the ‘big ditch’ or canal) between the Rhine and Danube. Excavations, dendrochronology and a re‐reading of Carolingian Annals shed new light on the chronology and setting of this canal, which was planned in 792, initiated in 793, and abandoned later that year. The abandonment is attested by both written and archaeological evidence. The different versions of the annals offer a unique opportunity for comparison with the archaeological record. Evidence that works of Vitruvius circulated in the Carolingian court suggests that Charlemagne’s advisers were drawing on classical tradition when they pitched the idea of digging the canal.

The prospection of (geo-)archaeological sites yield important knowledge about the concept and the utilisation of pre-historical and historical infrastructure. The satisfactory conduction of classical prospection methods like archaeological excavations or geoarchaeological vibra-coring might be challenging in the case of large sites or difficult underground conditions. This is particularly problematic in wetlands featuring a high groundwater table and high compaction rates of organic layers. In this study, we provide an alternative and non- to minimal-invasive exploration approach to discover hydro-engineering structures for artificial water supply in the surrounding of a Carolingian summit canal in South Germany. The Early Medieval Fossa Carolina was intended 792/793 CE to bridge the Central European watershed between Rhine-Main and Danube catchments. As the canal was constructed as a summit canal, an artificial water supply at the highest levels seemed very likely or even obligatory. In order to explore these obligatory hydro-engineering features, we use a wide range of on-site and off-site tools in a spatial hierarchical way. Our approach includes the large-scale SQUID magnetic survey and the sighting of historical maps. Furthermore, we integrate high-resolution direct push colour logs, and subsequent vibra-coring for small-scale stratigraphical verification and sedimentological analyses. The SQUID magnetic survey and related depth models discover two pronounced linear anomalies that might represent potential artificial water inlets in the North-Eastern and Northern Sections of the canal. 1) In the North-Eastern Section, direct push colour logs, vibra-coring and C-14 dating provide no evidence for a Carolingian hydro-engineering feature but reveal a natural lenticular structure of Early Holocene age.II) The linear magnetic anomaly in the Northern Section can be excluded with high probability as a hydro-engineering structure as well. Here, direct push colour logs, vibra-coring, C-14 dating and the comparison with a historic map reveal evidence for a historic gravel road. Thus, we have nicely verified the magnetic information but have no prove for an artificial Carolingian water inlet from the Swabian Rezat River that contradicts with assumptions of former studies. (C) 2020 The Authors. Published by Elsevier B.V.

Magnetometry is a well-established geo-physical method in archaeological prospection. Conservative techniques, however, do need high investment in labour and are comparatively slow. New quantum-based sensors (SQUIDs) have been innovating this methodological field through their ground breaking fastness in data collection, enormous magnetic field gradient resolution as well as the maximum of measurable magnetic information enabling depth and geometry reconstruction of the detected buried objects (magnetic inversion). Thus, the SQUID measuring system of Leibniz IPHT and Supracon AG, Jena (Linzen et al., 2007), see Fig. 1, has been successfully applied worldwide for widely different large-scale archaeological sites: be that the settlement regions of the Nasca and Palpa cultures in Peru or the Fossa Carolina in southern Germany, a miles long channel ordered by Charlemagne to link the Rhine-Main and the AltmuhlDanube inland navigation systems (Linzen and Schneider, 2014). Likewise, the system has been successfully transferred to Mongolia (Bemmann et al., 2011). Here, an additional feature of the SQUID instrument was intensively used – the simultaneous recording of high-resolution topographic information via the differential GPS and the inertial unit of the motorized system. Thus, two qualitatively different maps (magnetogram and topography) are gathered with high precision in geo-reference at the same time and with high speed. To bring the most modern standards in magnetometry to a developing country and further the scientific exchange is of high importance. At the same time, the pioneering aspect of the system which is constantly being refined through the field experience and close analysis of the data in transdisciplinary dialogue between the physicists and archaeologists need to be emphasized. The Mongolian steppes offer an ideal ground for this endeavour with its unique cultural heritage formed amongst others by large fixed habitation sites of ancient times generally untouched by later building activities or other anthropogenic intrusions. Thinking of the Mongolian steppes, cities do not immediately spring to mind. One rather thinks of traditional pastoral lifeways, living in yurts, sheep and above all horses. And yet, at some focal points in Mongolian history, cities played imminent roles in the steppe: first under the Uighur and most prestigiously under the Great Khans during the time of the Mongol Empire, the largest contiguous empire in World History. From the time of the 13 and 14 centuries Karakorum, the first capital of the Mongol Empire, has been a research focus of Bonn University for the past 20 years (Bemmann, Erdenebat & Pohl 2010). After having successfully applied the SQUID system to Karakorum in 2016 and 2017, another study of a contemporary site in order to have a comparative reference was sorely needed. Khar Khul Khaany Balgas, situated in the Khanui valley near the modern administrative centre of Erdenemandal, Arkhangai province (see Fig. 2) proved to be a perfect locality, ideally suited for SQUID-measurements as well as archaeological works. The site has never been encroached upon by later building activities, it is located in a wide flat plain on the first terrace of the river that flows nearby to the west of it, its archaeological find material and relative height of cultural levels as seen in the topography indicate that it has only been used during the old Mongol period with few settlement phases at the most. Furthermore, only few spots of the city have been touched by previous archaeologists, thus being a mostly undisturbed and an understudied site at the same time. Preparatory to the geomagnetic survey, to define the extent of the city and thus the area to be measured as well as to clean the city from metal waste contamination, an intensive, systematic, field walking survey was applied by the archaeological project team under the auspices of the DFG Collaborative Research Center 1167 “Macht und Herrschaft. International Conference on Cultural Heritage and New Technologies | Vienna | 2019 2 Premodern Configurations in Transcultural Perspective” at Bonn University in 2017. The project looks into how Mongol rulers used cities as a way of legitimizing their authority and how their authority is expressed via monuments, infrastructure and symbolic material culture in the landscape. The SQUID instrument was applied in Khar Khul Khaany Balgas to map an area of nearly 300 hectares (3 million square metres) within 23 measurement days in June 2018. An average distance of 100 measurement line kilometres per day were driven with a cross-country car pulling the cart over the steppe area (see Fig. 1). During the measurements the battery driven data acquisition on the cart records the magnetic data from each of the 18 SQUID sensors with a sampling frequency of 1000 Hz. Further, the differential GPS data from a Trimble 5700 receiver is recorded with 10 Hz and the Euler angles representing the tilt of the measurement cart which is monitored by a Xsens inertial unit is sampled with 100 Hz. These data streams result in a very high measurement point density of approximately 400 per square metre for the magnetic data and an amount of raw data of about 4 Gigabyte per day. More details about the technique of the SQUID instrument and the data post processing can be found in Linzen et al. (2007). The basis of the topographic data is a differential GPS setup which consists of one receiver mounted onto the measurement cart as rover and a second one fixed as base station. The latter was positioned on top of the north corner of the main walled enclosure (see Fig. 2). The current position of the cart has always been calculated in real time with the highest available precision (RTK fixed mode). Thus, the vertical position error was limited to a few centimetres allowing the detection of tiny altitude variations mostly caused by archaeological remains. The Mongolian steppe with its permanent dust exposure and extreme temperature variations is a challenge for the measurement technique as well as the operators. The SQUID prospection technique, however, worked absolutely reliable. Additional expenses and skills for the liquid helium sensor cooling were required, but led a priori to a temperature stabilisation of all sensors and a prevention of drift effects. Through combined multidisciplinary analyses of magnetic anomalies, topographic features and the distribution of find materials gathered through the initial pedestrian survey, new insights into the city’s layout, the use and function of certain building features and even down to the constructional make-up of the buildings themselves are won. These results will be highlighted through a discussion of the overall structure of the city, leading to the immanent question of whether the city has grown organically and developed from the bottom up or if we have rather indications for a top-down-planning and a supervised, thoroughly planned construction of the city. Details taken from the combined analyses will pull the scale to individual features within the city: the assumed Buddhist temple shows revealing similarities in its orientation to Karakorum’s temple of the Rising Yuan, its constructional make-up with fired bricks is clearly demonstrated in the magnetic measurements and confirmed by the archaeological mapping of building materials. Further examples include the main compound, assumably the palace area, and particular constructions on the crossroads of the major streets. Working closely together with the local authorities in the administrative center Erdenemandal, the new mapping of Khar Khul Khaany Balgas exerts its usefulness on different levels: first and foremost it shows the archaeological substance in hitherto unknown detail, and second, it thus provides a definite basis for the creation of areas of cultural protection. All results will be shared with the local government to ensure that protective steps are undertaken in the near future, a fundamental necessity to preserve this important heritage for generations to come.

The Early Medieval Fossa Carolina is the first hydro-engineering construction that bridges the Central European Watershed. The canal was built in 792/793 AD on order of Charlemagne and should connect the drainage systems of the Rhine-Main catchment and the Danube catchment. In this study, we show for the first time, the integration of Airborne LiDAR (Light Detection and Ranging) and geoarchaeological subsurface datasets with the aim to create a 3D-model of Charlemagne’s summit canal. We used a purged Digital Terrain Model that reflects the pre-modern topography. The geometries of buried canal cross-sections are derived from three archaeological excavations and four high-resolution direct push sensing transects. By means of extensive core data, we interpolate the trench bottom and adjacent edges along the entire canal course. As a result, we are able to create a 3D-model that reflects the maximum construction depth of the Carolingian canal and calculate an excavation volume of approx. 297,000 m3. Additionally, we compute the volume of the present dam remnants by Airborne LiDAR data. Surprisingly, the volume of the dam remnants reveals only 120,000 m3 and is much smaller than the computed Carolingian excavation volume. The difference reflects the erosion and anthropogenic overprint since the 8th century AD.

The full waveform inversion (FWI) of strongly dispersive Love wave data is a challenging task. Amplitude, phase and dispersion information not only depends on the density and shear modulus distribution in the subsurface, but also significantly on intrinsic damping. This is especially a problem in near surface data applications with complex underground structures and low Qs values. Therefore, the FWI of a dispersive Love wavefield demands an accurate initial visco-elastic model and careful data pre-processing. Another key ingredient of a successful time-domain FWI is the sequential inversion of frequency filtered data in order to mitigate the non-linearity of the inverse problem. Common FWI strategies are based solely on either low- or bandpass filtered data. In this study we develop an FWI workflow consisting of a combined low- and bandpass filter strategy to achieve an appropriate data fit of the low-frequency Love wave and high-frequency refracted SH-wavefield. The applicability of this FWI strategy and the importance of a visco-elastic medium description is demonstrated for SH field data from a transect over the Fossa Carolina, a silted medieval canal structure in southern Germany. The resolved canal shape and small scale structures in the inversion results are verified by an archaeological excavation.

In this manuscript we document a multidisciplinary approach in wetland geoarchaeology for detecting artificial structures in a middle European floodplain. By means of a large set of different prospection methods (cadastral analysis, aerial archaeology, LiDAR, SQUID based magnetic prospection, electrical resistivity tomography, seismic refraction tomography, ground penetrating radar) and a subsequent geoarchaeological drilling campaign we provide an overview about the potentials and limits of the applied methods. Our site-specific aims focus on the Fossa Carolina, Charlemagne's shortcut for linking the Rhine-Main and the Altmuhl-Danube inland navigation systems during the Early Middle Ages. Our results show that Altmuhl meander loops were quasi stable since Carolingian times and that an Altmuhl floodplain-crossing trench of at least 650-700 m was required for linking the Altmuhl River with the - archaeological known - southernmost position of the existing Carolingian canal. However, our large set of remote sensing and geophysical prospection tools and the corresponding drilling campaign do not show any evidence for the missing Carolingian trench within the Altmuhl floodplain. Our results support the idea that the Carolingian canal was never entirely completed although large parts of the canal were almost finished in the northern sections. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.