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Unconventional Josephson effect in two dimensional electron gas-based superconductor-semiconductor Josephson junctions

Kaveh Delfanazari, Peng‐Cheng Ma, Ian A. Farrer, D. A. Ritchie, Hannah Jane Joyce, M J Kelly, Christina H. Smith

Published Oct 5, 2018• 0 citations
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Abstract

Further to the development of scalable hybrid quantum circuits introduced by us [1-5], here we report on the discovery of an unconventional Josephson effect in hybrid In0.75Ga0.25As two-dimensional electron gas-Nb junctions that are designed and fabricated for scalable hybrid quantum circuit integration. Reference: [1] K. Delfanazari, et al, Adv. Mater. 29, 1701836 (2017). [2] K. Delfanazari, et al, J. Magn. Magn. Mater. 459, 282-284 (2018). [3] K. Delfanazari, et al, IEEE Trans. Appl. Supercond. 28, 1100304 (2018).

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...we introduced an integrated circuit consisting of arrays of planar Josephson junctions based on two-dimensional electron gas (2DEG) in In0.75Ga0.25As heterostructure. The methods that are used for ballistic 2D Josephson junction and hybrid quantum integrated circuit fabrication will be demonstrated. Furthermore, the temperature and magnetic field dependencies of the phase coherent quantum transport in 2D Josephson junctions, the induced superconducting properties into 2DEG, and the subharmonic energy gap structures (SGS) due to Andreev reflections at the S-Sm interfaces will be discussed. Reference: [1] K. Delfanazari, et al, Adv. Mater. 29, 1701836 (2017). [2] K. Delfanazari, et al, J. Magn. Magn. Mater. 459, 282-284 (2018). [3] K. Delfanazari, et al, IEEE Trans. Appl. Supercond. 28, 1100304 (2018).

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Further to the development of scalable hybrid quantum circuits introduced by us [1-5], here we report on the discovery of an unconventional Josephson effect in hybrid In0.75Ga0.25As two-dimensional electron gas-Nb junctions that are designed and fabricated for scalable hybrid quantum circuit integration. Reference: [1] K. Delfanazari, et al, Adv. Mater. 29, 1701836 (2017). [2] K. Delfanazari, et al, J. Magn. Magn. Mater. 459, 282-284 (2018). [3] K. Delfanazari, et al, IEEE Trans. Appl. Supercond. 28, 1100304 (2018).
...we introduced an integrated circuit consisting of arrays of planar Josephson junctions based on two-dimensional electron gas (2DEG) in In0.75Ga0.25As heterostructure. The methods that are used for ballistic 2D Josephson junction and hybrid quantum integrated circuit fabrication will be demonstrated. Furthermore, the temperature and magnetic field dependencies of the phase coherent quantum transport in 2D Josephson junctions, the induced superconducting properties into 2DEG, and the subharmonic energy gap structures (SGS) due to Andreev reflections at the S-Sm interfaces will be discussed. Reference: [1] K. Delfanazari, et al, Adv. Mater. 29, 1701836 (2017). [2] K. Delfanazari, et al, J. Magn. Magn. Mater. 459, 282-284 (2018). [3] K. Delfanazari, et al, IEEE Trans. Appl. Supercond. 28, 1100304 (2018).
In this paper, we experimentally demonstrate a hybrid superconducting-semiconducting circuit consisting of eight planar and ballistic Nb-In0.75Ga0.25As-Nb Josephson junctions. E-beam lithography was used to fabricate the Josephson junctions on an InGaAs chip. In contrast to our previous studies on long junctions that were fabricated by photolithography, in this study, we observe the induced superconductivity in an In0.75Ga0.25As quantum well at higher temperatures, between T = 0.3 and 1 K (3He cryostat temperature range). The induced superconducting gap of Δind= 0.65 meV was measured at lowest base temperature T = 300 mK. The effect of temperature and magnetic fields B on the induced superconductivity are presented. Our results suggest that our In0.75Ga0.25As heterostructure is a promising scalable material system for quantum processing and computing applications.
Hybrid semiconductor-superconductor qubits have recently emerged as a promising alternative to traditional platforms, combining material advantages with device-level tunability. A defining feature is their gate-tunable Josephson coupling, enabling superconducting qubit architectures with full electric-field control and offering a path toward scalable, low-crosstalk quantum processors. This approach seeks to merge benefits of superconducting and semiconductor qubits, for instance by encoding quantum information in the spin of a quasiparticle occupying an Andreev bound state, thus combining long coherence times with fast, flexible control. Progress has accelerated through bottom-up engineering of Andreev states in coupled quantum dot arrays, leading to architectures such as minimal Kitaev chains hosting Majorana zero modes. In parallel, Hamiltonian-protected designs aim to enhance resilience against local noise and decoherence by exploiting superconducting phase dynamics and discrete charge or flux degrees of freedom. This article reviews recent theoretical and experimental advances in hybrid qubits, providing an overview of physical mechanisms, device implementations, and emerging architectures, with emphasis on their potential for (topologically) protected quantum information processing. While many designs remain at proof-of-concept stage, rapid progress suggests practical demonstrations may soon be achievable.