Stefano Bosco
ContactDepartment of PhysicsUniversity of Basel Klingelbergstrasse 82 CH4056 Basel, Switzerland

Short CV
2019  present  Postdoc, University of Basel, Switzerland with Prof. Daniel Loss 
2015  2019  Ph.D. in Condensed matter physics, RWTH Aachen University, Germany 
Supervisor: Prof. David P. DiVincenzo  
2013  2015  M. Sc. in Nanoscience and Nanotechnology, 
Erasmus Mundus in: Katholieke Universiteit Leuven, Belgium and Chalmers Tekniska Hogskola, Sweden.  
2010  2013  Bachelor degree in Electronics Engineering, Politecnico di Milano, Italy. 
Publications
Show all abstracts.1.  Hole Spin Qubits in Ge Nanowire Quantum Dots: Interplay of Orbital Magnetic Field, Strain, and Growth Direction 
Christoph Adelsberger, Mónica Benito, Stefano Bosco, Jelena Klinovaja, and Daniel Loss. arXiv:2110.15039 (2021)  
2.  Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots 
Stefano Bosco and Daniel Loss. Phys. Rev. Lett. 127, 190501 (2021)  
3.  Squeezed hole spin qubits in Ge quantum dots with ultrafast gates at low power 
Stefano Bosco, Mónica Benito, Christoph Adelsberger, and Daniel Loss. Phys. Rev. B 104, 115425 (2021)  
4.  Hole Spin Qubits in Si FinFETs With Fully Tunable SpinOrbit Coupling and Sweet Spots for Charge Noise 
Stefano Bosco, Bence Hetényi, and Daniel Loss. PRX Quantum 2, 010348 (2021)  
5.  Strong spinorbit interaction and gfactor renormalization of hole spins in Ge/Si nanowire quantum dots 
F. N. M. Froning, M. J. Rančić, Bence Hetényi, Stefano Bosco, M. K. Rehmann, A. Li, E. P. A. M. Bakkers, F. A. Zwanenburg, Daniel Loss, D. M. Zumbühl, and F. R. Braakman. Phys. Rev. Research 3, 013081 (2021)  
6.  HardwareEncoding Grid States in a NonReciprocal Superconducting Circuit 
Martin Rymarz, Stefano Bosco, Alessandro Ciani, and David P. DiVincenzo. Phys. Rev. X 11, 011032 (2021)  
7.  Simulating moving cavities in superconducting circuits 
Stefano Bosco, Joel Lindkvist, and Göran Johansson. Phys. Rev. A 100, 023817 (2019)
We theoretically investigate the simulation of moving cavities in a superconducting circuit setup. In particular, we consider a recently proposed experimental scenario where the phase of the cavity field is used as a moving clock. By computing the error made when simulating the cavity trajectory with superconducting quantum interference devices (SQUIDs), we identify parameter regimes where the correspondence holds, and where time dilation and corrections due to clock size and to particle creation coefficients are observable. These findings may serve as a guideline when performing experiments on simulation of moving cavities in superconducting circuits.
 
8.  Transmission lines and resonators based on quantum Hall plasmonics: Electromagnetic field, attenuation, and coupling to qubits 
Stefano Bosco and David P. DiVincenzo. Phys. Rev. B 100, 035416 (2019)
Quantum Hall edge states have some characteristic features that can prove useful to measure and control solid state qubits. For example, their high voltage to current ratio and their dissipationless nature can be exploited to manufacture lowloss microwave transmission lines and resonators with a characteristic impedance of the order of the quantum of resistance h/e^2∼25kΩ. The high value of the impedance guarantees that the voltage per photon is high, and for this reason, highimpedance resonators can be exploited to obtain larger values of coupling to systems with a small charge dipole, e.g., spin qubits. In this paper, we provide a microscopic analysis of the physics of quantum Hall effect devices capacitively coupled to external electrodes. The electrical current in these devices is carried by edge magnetoplasmonic excitations and by using a semiclassical model, valid for a wide range of quantum Hall materials, we discuss the spatial profile of the electromagnetic field in a variety of situations of interest. Also, we perform a numerical analysis to estimate the lifetime of these excitations and, from the numerics, we extrapolate a simple fitting formula which quantifies the Q factor in quantum Hall resonators. We then explore the possibility of reaching the strong photonqubit coupling regime, where the strength of the interaction is higher than the losses in the system. We compute the Coulomb coupling strength between the edge magnetoplasmons and singlettriplet qubits, and we obtain values of the coupling parameter in the order of 100 MHz; comparing these values to the estimated attenuation in the resonator, we find that for realistic qubit designs the coupling can indeed be strong.
 
9.  Transmission Lines and Metamaterials Based on Quantum Hall Plasmonics 
Stefano Bosco, David P. DiVincenzo, and David J. Reilly. Phys. Rev. Applied 12, 014030 (2019)
The characteristic impedance of a microwave transmission line is typically constrained to a value Z0=50Ω, in part because of the low impedance of free space and the limited range of permittivity and permeability realizable with conventional materials. Here we suggest the possibility of constructing highimpedance transmission lines by exploiting the plasmonic response of edge states associated with the quantum Hall effect in gated devices. We analyze various implementations of quantum Hall transmission lines based on distributed networks and lumpedelement circuits, including a detailed account of parasitic capacitance and Coulomb drag effects, which can modify device performance. We additionally conceive of a metamaterial structure comprising arrays of quantum Hall droplets and analyze its unusual properties. The realization of such structures holds promise for efficiently wiringup quantum circuits on chip, as well as engineering strong coupling between semiconductor qubits and microwave photons.
 
10.  Nonreciprocal quantum Hall devices with driven edge magnetoplasmons in twodimensional materials 
Stefano Bosco and David P. DiVincenzo. Phys. Rev. B 95, 195317 (2017)
We develop a theory that describes the response of nonreciprocal devices employing twodimensional materials in the quantum Hall regime capacitively coupled to external electrodes. As the conduction in these devices is understood to be associated to the edge magnetoplasmons (EMPs), we first investigate the EMP problem by using the linear response theory in the random phase approximation. Our model can incorporate several cases that were often treated on different grounds in literature. In particular, we analyze plasmonic excitations supported by a smooth and sharp confining potential in a twodimensional electron gas, and in monolayer graphene, and we point out the similarities and differences in these materials. We also account for a general timedependent external drive applied to the system. Finally, we describe the behavior of a nonreciprocal quantum Hall device: the response contains additional resonant features, which were not foreseen from previous models.
 
11.  SelfImpedanceMatched HallEffect Gyrators and Circulators 
Stefano Bosco, Federica Haupt, and David P. DiVincenzo. Phys. Rev. Applied 7, 024030 (2017)
We present a model study of an alternative implementation of a twoport Halleffect microwave gyrator. Our setup involves three electrodes, one of which acts as a common ground for the others. Based on the capacitivecoupling model of Viola and DiVincenzo, we analyze the performance of the device and we predict that ideal gyration can be achieved at specific frequencies. Interestingly, the impedance of the threeterminal gyrator can be made arbitrarily small for certain coupling strengths, so that no auxiliary impedance matching is required. Although the bandwidth of the device shrinks as the impedance decreases, it can be improved by reducing the magnetic field; it can be realistically increased up to 150 MHz at
50Ω by working at the filling factor ν=10. We also examine the effects of the parasitic capacitive coupling between electrodes and we find that, although, in general, they strongly influence the response of device, their effect is negligible at low impedance. Finally, we analyze an interferometric implementation of a circulator, which incorporates the gyrator in a MachZender–like construction. Perfect circulation in both directions can be achieved, depending on frequency and on the details of the interferometer.
 
12.  A model study of presentday Halleffect circulators 
Benedikt Placke, Stefano Bosco, and David P. DiVincenzo. EPJ Quantum Technol. 4, 5 (2017)
Stimulated by the recent implementation of a threeport Halleffect microwave circulator of Mahoney et al. (MEA), we present model studies of the performance of this device. Our calculations are based on the capacitivecoupling model of Viola and DiVincenzo (VD). Based on conductance data from a typical Hallbar device obtained from a twodimensional electron gas (2DEG) in a magnetic field, we numerically solve the coupled fieldcircuit equations to calculate the expected performance of the circulator, as determined by the S parameters of the device when coupled to 50Ω ports, as a function of frequency and magnetic field. Above magnetic fields of 1.5 T, for which a typical 2DEG enters the quantum Hall regime (corresponding to a Landaulevel filling fraction ν of 20), the Hall angle θH=tan−1σxy/σxx always remains close to 90°, and the S parameters are close to the analytic predictions of VD for θH=π/2. As anticipated by VD, MEA find the device to have rather high (kΩ) impedance, and thus to be extremely mismatched to 50Ω, requiring the use of impedance matching. We incorporate the lumped matching circuits of MEA in our modeling and confirm that they can produce excellent circulation, although confined to a very small bandwidth. We predict that this bandwidth is significantly improved by working at lower magnetic field when the Landau index is high, e.g. ν=20, and the impedance mismatch is correspondingly less extreme. Our modeling also confirms the observation of MEA that parasitic porttoport capacitance can produce very interesting countercirculation effects.
