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Theory of Quantum-Classical Crossover

Artur Mendes Kur

Jan 1, 20260 citations

Effect of constriction width on hysteresis in superconducting weak links and micro-SQUIDs

Nikhil Kumar, Bharat Kumar Gupta, Anjan Kumar Gupta

We have fabricated and characterized niobium film based superconducting weak link (WL) devices and micron-size superconducting quantum interference devices (µ-SQUIDs) with superconducting WLs as Josephson Junctions. Here we discuss the effect of WL width on the hysteresis and crossover temperature (Th) while keeping the other dimensions fixed. We find that the critical current reduces linearly with the width and thus Th reduces with decreasing width. This makes some of the devices non-hysteretic down to 1.3K. We also discuss the observed excess current in the current-voltage characteristics of these devices, in terms of Andreev reflection.We have fabricated and characterized niobium film based superconducting weak link (WL) devices and micron-size superconducting quantum interference devices (µ-SQUIDs) with superconducting WLs as Josephson Junctions. Here we discuss the effect of WL width on the hysteresis and crossover temperature (Th) while keeping the other dimensions fixed. We find that the critical current reduces linearly with the width and thus Th reduces with decreasing width. This makes some of the devices non-hysteretic down to 1.3K. We also discuss the observed excess current in the current-voltage characteristics of these devices, in terms of Andreev reflection.

AIP conference proceedingsJan 1, 20210 citations

FerBo: a noise resilient qubit hybridizing Andreev and fluxonium states

J. J. Caceres, D. Sanz Marco, J. Ortuzar +6 more

We propose a novel superconducting quantum circuit that should be robust against both relaxation and dephasing over a wide and experimentally accessible parameter range. The circuit consists of a parallel arrangement of a large inductance, a small capacitor, and a well-transmitting Josephson weak link. Protection against relaxation arises from the hybridization between the fermionic degree of freedom associated with Andreev levels in the weak link and the bosonic electromagnetic mode of the LC circuit, hence its name: FerBo. Furthermore, as in the fluxonium qubit, delocalization of the wavefunctions in phase space provides resilience against dephasing.We propose a novel superconducting quantum circuit that should be robust against both relaxation and dephasing over a wide and experimentally accessible parameter range. The circuit consists of a parallel arrangement of a large inductance, a small capacitor, and a well-transmitting Josephson weak link. Protection against relaxation arises from the hybridization between the fermionic degree of freedom associated with Andreev levels in the weak link and the bosonic electromagnetic mode of the LC circuit, hence its name: FerBo. Furthermore, as in the fluxonium qubit, delocalization of the wavefunctions in phase space provides resilience against dephasing.

cond-mat.mes-hallCross-listedarXiv:2604.01145Apr 2, 20260 citations

The Quantum-Classical Crossover as Phase Transition

WORLD SCIENTIFIC eBooksMar 1, 20060 citations

The Quantum–Classical Crossover as Phase Transition

WORLD SCIENTIFIC eBooksSep 1, 20120 citations

Integrating quantum materials into superconducting qubits

Kuei-Lin Chiu, Avishma J. Lasrado, Cheng-Han Lo +3 more

Abstract In this perspective article, we review the current state of research on integrating quantum materials (QMs) into superconducting quantum devices. We begin with the role of QMs as weak links in Josephson junctions, enabling gate- and flux-tunable transmons. We then explore their application in more complex superconducting circuits, such as gate-tunable fluxonium qubits, or gatemonium, which provide additional control over qubit parameters. We also discuss QM-based vertical junctions and their potential for creating merged-element transmons. Further, we highlight QMs’ role in topological superconducting circuits, where they facilitate the study of Majorana zero modes through signatures such as 4π-periodic supercurrents. Additionally, we review the integration of QMs into 3D cavity architectures and discuss how they differ from their 2D counterparts. Beyond weak links, we examine the use of 2D superconducting and insulating materials, such as NbSe2 and hBN, in parallel-plate capacitors, offering a compact alternative to conventional large-footprint transmon capacitors. Finally, we outline the current challenges and future directions for exploration.Abstract In this perspective article, we review the current state of research on integrating quantum materials (QMs) into superconducting quantum devices. We begin with the role of QMs as weak links in Josephson junctions, enabling gate- and flux-tunable transmons. We then explore their application in more complex superconducting circuits, such as gate-tunable fluxonium qubits, or gatemonium, which provide additional control over qubit parameters. We also discuss QM-based vertical junctions and their potential for creating merged-element transmons. Further, we highlight QMs’ role in topological superconducting circuits, where they facilitate the study of Majorana zero modes through signatures such as 4π-periodic supercurrents. Additionally, we review the integration of QMs into 3D cavity architectures and discuss how they differ from their 2D counterparts. Beyond weak links, we examine the use of 2D superconducting and insulating materials, such as NbSe2 and hBN, in parallel-plate capacitors, offering a compact alternative to conventional large-footprint transmon capacitors. Finally, we outline the current challenges and future directions for exploration.

Materials for Quantum TechnologyMay 13, 20251 citation

The quantum to classical crossover for a weak link capacitor

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