Gaia Germanese, Federico Paolucci, Giampiero Marchegiani, Alessandro Braggio, and Francesco Giazotto
Phys. Rev. Applied 19, 014074 – Published 31 January 2023

Herein, Italian scientists: Dr. Gaia Germanese, Dr. Federico Paolucci, Dr. Alessandro Braggio and Dr. Francesco Giazotto from NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore in collaboration with Dr. Giampiero Marchegiani from Technology Innovation Institute Abu Dhabi investigated the bipolar thermoelectric effect in Josephson junctions. In particular, they focused on phase control and the effect of Josephson contribution on the thermoelectricity modulation of Cooper pair’s transport. Their research work is currently published in the peer-reviewed journal, Physical Review Applied.

The quartic Blochnium: an anharmonic quasicharge superconducting qubit
Luca Chirolli, Matteo Carrega, Francesco Giazotto
arXiv:2304.10401 [cond-mat.mes-hall]

The quasicharge superconducting qubit realizes the dual of the transmon and shows strong robustness to flux and charge fluctuations thanks to a very large inductance closed on a Josephson junction. At the same time, a weak anharmonicity of the spectrum is inherited from the parent transmon, that introduces leakage errors and is prone to frequency crowding in multi-qubit setups. We propose a novel design that employs a quartic superinductor and confers a good degree of anharmonicity to the spectrum. The quartic regime is achieved through a properly designed chain of Josephson junction loops that avoids strong quantum fluctuations without introducing a severe dependence on the external flux.

Topological Josephson Junctions in the Integer Quantum Hall Regime
Gianmichele Blasi, Géraldine Haack, Vittorio Giovannetti, Fabio Taddei, Alessandro Braggio
arXiv: 2211.02575 [cond-mat.mes-hall]

Robust and tunable topological Josephson junctions (TJJs) are highly desirable platforms for investigating the anomalous Josephson effect and topological quantum computation applications. Experimental demonstrations have been done in hybrid superconducting-two dimensional topological insulator (2DTI) platforms, sensitive to magnetic disorder and interactions with phonons and other electrons. In this work, we propose a robust and electrostatically tunable TJJ by combining the physics of the integer quantum Hall (IQH) regime and of superconductors. We provide analytical insights about the corresponding Andreev bound state spectrum, the Josephson current and the anomalous current. We demonstrate the existence of protected zero-energy crossings, that can be controlled through electrostatic external gates. This electrostatic tunability has a direct advantage to compensate for non-ideal interfaces and undesirable reflections that may occur in any realistic samples. TJJs in the IQH regime could be realized in graphene and other 2D materials. They are of particular relevance towards scalable and robust Andreev-qubit platforms, and also for efficient phase batteries.

Estimation of the FR4 Microwave Dielectric Properties at Cryogenic Temperature for Quantum-Chip-Interface PCBs Design
A. Paghi, G. Trupiano, C. Puglia, H. Burgaud, G. De Simoni, A. Greco, F. Giazotto
arXiv:2310.01171 [physics.ins-det]

Ad-hoc interface PCBs are today the standard connection between cryogenic cabling and quantum chips. Besides low-loss and low-temperature-dependent-dielectric-permittivity materials, FR4 provides a low-cost solution for fabrication of cryogenic PCBs. Here, we report on an effective way to evaluate the dielectric performance of a FR4 laminate used as substrate for cryogenic microwave PCBs. We designed a coplanar waveguide {\lambda}/2 open-circuit series resonator and we fabricated the PCB using a low-cost manufacturing process. Such a geometry allows to exploit the resonance peak of the resonator to measure the variation of the complex dielectric permittivity as a function of the temperature. Resonance peak frequency and magnitude were used as sensing parameters for the real part of dielectric permittivity and dielectric loss tangent, respectively. We estimated a 9 % reduction of the real part of the dielectric permittivity and a 70 % reduction of the dielectric loss tangent in the temperature range from 300 to 4 K. The proposed approach can be immediately extended to the detection of cryogenic temperature-dependent dielectric performance of any kind on substrate.