Josephson current via an isolated Majorana zero mode

We study the equilibrium dc Josephson current in a junction between an s-wave and a topological superconductor. Cooper pairs from the s-wave superconducting lead can transfer to the topological side either via an unpaired Majorana zero mode localized near the junction or via the above-gap continuum states. We find that the Majorana contribution to the supercurrent can be switched on when time-reversal symmetry in the conventional lead is broken, e.g., by an externally applied magnetic field inducing a Zeeman splitting. Moreover, if the magnetic field has a component in the direction of the effective spin-orbit field, there will be a Majorana-induced anomalous supercurrent at zero phase difference. These behaviors may serve as a signature characteristic of Majorana zero modes and are accessible to devices with only superconducting contacts.QRD/Wimmer LabBUS/Quantum Delf

The added value of smart stadiums: A case study at Johan Cruijff Arena

PurposeThe objective of stadium owners is to attract visitors to their stadiums and by this optimally use their business potential. Stadiums face increasing competition from home-viewing options, with which especially aging stadiums have trouble competing. This paper aims to study the concept of smart stadiums as a solution to this problem, adding the corona age as an additional challenge.Design/methodology/approachFirst, (smart) stadium literature and theories are reviewed. Then, a case study is conducted, consisting of document review, observations and semi-structured interviews with specialists. The case that is studied is the Johan Cruijff Arena in Amsterdam – the stadium has the ambition to be the most innovative stadium in 2020.FindingsNine different smart tools were identified in the case study, which supports the optimization of various processes in the stadium such as ticketing and crowd control. The findings from this case study showed the potential of the smart stadium concept and how it can add value for the stadium’s stakeholders. The use of smart tools can improve the effectiveness and efficiency of stadium operations, and it can be used to improve the visitors’ experience. However, concrete numbers of progress were difficult to obtain because the smart tools were only recently implemented.Originality/valueAs seen in the past few years, more and more stadiums are branding themselves as a smart stadium. However, research on this subject is still scarce: existing research focused on other types of real estate. By exploring the work done in theory and practice, the authors hope to increase research on the subject of smart stadiums.Accepted Author ManuscriptCRE Strategic Portfolio Management - Asset ManagementReal Estate Managemen

Energy spectrum and current-phase relation of a nanowire Josephson junction close to the topological transition

A semiconducting nanowire proximitized by an s-wave superconductor can be tuned into a topological state by an applied magnetic field. This quantum phase transition is marked by the emergence of Majorana zero modes at the ends of the wire. The fusion of Majorana modes at a junction between two nanowires results in a 4π-periodic Josephson effect. We elucidate how the 4π periodicity arises across the topological phase transition in a highly-transparent short nanowire junction. Owing to a high transmission coefficient, Majorana zero modes coming from different wires are strongly coupled, with an energy scale set by the proximity-induced, field-independent pairing potential. At the same time, the topological spectral gap-defined by competition between superconducting correlations and Zeeman splitting-becomes narrow in the vicinity of the transition point. The resulting hybridization of the fused Majorana states with the spectral continuum strongly affects the electron density of states at the junction and its Josephson energy. We study the manifestations of this hybridization in the energy spectrum and phase dependence of the Josephson current. We pinpoint the experimentally observable signatures of the topological phase transition, focusing on junctions with weak backscattering.QRD/Kouwenhoven La

Quantum critical dynamics of a Josephson junction at the topological transition

We find the admittance of a Josephson junction at or near a topological transition. The dependence of the admittance on frequency and temperature at the critical point is universal and determined by the symmetries of the system. Despite the absence of a spectral gap at the transition, the dissipative response may remain weak at low energies: . This behavior is strikingly different from the electromagnetic response of a normal metal. Away from the critical point, the scaling functions for the dependence of the admittance on frequency and temperature are controlled by at most two parameters.BUS/Quantum Delf

Combining Insar, levelling and GNSS for the estimation of 3D surface displacements

The three geodetic techniques InSAR, levelling and GNSS are complementary w.r.t. (i) the sensitivity to horizontal and vertical displacement components, (ii) the spatial and temporal resolution of the measurements and (iii) the accuracy of the resulting displacements. We present a strategy to robustly combine the displacement estimates of the three techniques with a focus on long-term, linear movements. The linear displacement rates from InSAR in ascending and descending image geometry are combined with vertical and horizontal rates from levelling and GNSS, respectively, resulting in 3D velocity vectors at a dense surface grid. The results of our combination approach indicate that it is possible to derive realistic surface movements on the sub-mm/a scale with significance.Mathematical Geodesy and Positionin

Full parity phase diagram of a proximitized nanowire island

We measure the charge periodicity of Coulomb blockade conductance oscillations of a hybrid InSb-Al island as a function of gate voltage and parallel magnetic field. The periodicity changes from to at a gate-dependent value of the magnetic field, , decreasing from a high to a low limit upon increasing the gate voltage. In the gate voltage region between the two limits, which our numerical simulations indicate to be the most promising for locating Majorana zero modes, we observe correlated oscillations of peak spacings and heights. For positive gate voltages, the transition with low is due to the presence of nontopological states whose energy quickly disperses below the charging energy due to the orbital effect of the magnetic field. Our measurements highlight the importance of a careful exploration of the entire available phase space of a proximitized nanowire as a prerequisite to define future topological qubits.Architecture and the Built EnvironmentQuTechQCD/Veldhorst LabBUS/Quantum DelftQRD/Kouwenhoven LabOptical and Laser Remote SensingQN/Kouwenhoven La

Gate-Tunable Kinetic Inductance in Proximitized Nanowires

We report the detection of a gate-tunable kinetic inductance in a hybrid InAs/Al nanowire. For this purpose, we embed the nanowire into a quarter-wave coplanar waveguide resonator and measure the resonance frequency of the circuit. We find that the resonance frequency can be changed via the gate voltage that controls the electron density of the proximitized semiconductor and thus the nanowire inductance. Applying Mattis-Bardeen theory, we extract the gate dependence of the normal-state conductivity of the nanowire, as well as its superconducting gap. Our measurements complement existing characterization methods for hybrid nanowires and provide a useful tool for gate-controlled superconducting electronics. QRD/Kouwenhoven LabQN/Andersen La

Unified numerical approach to topological semiconductor-superconductor heterostructures

We develop a unified numerical approach for modeling semiconductor-superconductor heterostructures. All the key physical ingredients of these systems - orbital effect of magnetic field, superconducting proximity effect, and electrostatic environment - are taken into account on equal footing in a realistic device geometry. As a model system, we consider indium arsenide (InAs) nanowires with an epitaxial aluminum (Al) shell, which is one of the most promising platforms for Majorana zero modes. We demonstrate qualitative and quantitative agreement of the obtained results with the existing experimental data. Finally, we characterize the topological superconducting phase emerging in a finite magnetic field and calculate the corresponding topological phase diagram.QRD/Wimmer La

Dynamical Polarization of the Fermion Parity in a Nanowire Josephson Junction

Josephson junctions in InAs nanowires proximitized with an Al shell can host gate-tunable Andreev bound states. Depending on the bound state occupation, the fermion parity of the junction can be even or odd. Coherent control of Andreev bound states has recently been achieved within each parity sector, but it is impeded by incoherent parity switches due to excess quasiparticles in the superconducting environment. Here, we show that we can polarize the fermion parity dynamically using microwave pulses by embedding the junction in a superconducting LC resonator. We demonstrate polarization up to 94%±1% (89%±1%) for the even (odd) parity as verified by single shot parity readout. Finally, we apply this scheme to probe the flux-dependent transition spectrum of the even or odd parity sector selectively, without any postprocessing or heralding.QRD/Kouwenhoven LabQN/Wimmer GroupBUS/Quantum Delf

Singlet-Doublet Transitions of a Quantum Dot Josephson Junction Detected in a Transmon Circuit

We realize a hybrid superconductor-semiconductor transmon device in which the Josephson effect is controlled by a gate-defined quantum dot in an InAs-Al nanowire. Microwave spectroscopy of the transition spectrum of the transmon allows us to probe the ground-state parity of the quantum dot as a function of the gate voltages, the external magnetic flux, and the magnetic field applied parallel to the nanowire. The measured parity phase diagram is in agreement with that predicted by a single-impurity Anderson model with superconducting leads. Through continuous-time monitoring of the circuit, we furthermore resolve the quasiparticle dynamics of the quantum dot Josephson junction across the phase boundaries. Our results can facilitate the realization of semiconductor-based 0-π qubits and Andreev qubits.QRD/Kouwenhoven LabQuTechQN/Andersen LabQN/Kouwenhoven La