Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session A15: Superconductivity: Proximity Effects I |
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Sponsoring Units: DCMP Chair: Paula Fekete, US Military Academy West Point Room: M100F |
Monday, March 4, 2024 8:00AM - 8:12AM |
A15.00001: Controlling Majorana hybridization in magnetic chain-superconductor systems Oladunjoye A Awoga We propose controlling the hybridization between Majorana zero modes at the ends of magnetic adatom chains on superconductors by an additional magnetic adatom deposited close by. By tuning the additional adatom's magnetization, position, and coupling to the superconductor, we can couple and decouple the Majorana modes as well as control the ground state parity. The scheme is independent of microscopic details in ferromagnetic and helical magnetic chains on superconductors with and without spin-orbit coupling, which we show by studying their full microscopic models and their common low-energy description. Our results show that scanning tunneling microscopy and electron spin resonance techniques are promising tools for controlling the Majorana hybridization in magnetic adatoms-superconductor setups, providing a basis for Majorana parity measurements, fusion, and braiding techniques. |
Monday, March 4, 2024 8:12AM - 8:24AM |
A15.00002: Proximity Effects in AlGaSb/InAs surface quantum wells Emma A Bergeron, Francois Sfigakis, Ahmed Elbaroudy, Fiona Thompson, George Nichols, Yinqiu Shi, Man Chun Tam, Zbigniew Wasilewski, Jonathan D Baugh We demonstrate a robust superconducting proximity effect in 24 nm wide AlGaSb/InAs surface quantum wells with sputtered Nb contacts at a temperature of 1.6 K, which has applications towards mesoscopic and topological superconductivity. Through transport characterization we observe high quality single-subband and second subband magnetotransport with quantized integer quantum Hall plateaus observed to filling factor ν = 2 in magnetic fields of up to B = 18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinchoff to 3 x 1012 cm-2. Landau fan diagrams at high densities exhibit features from the crossing of spin-split Landau levels from different subbands and curvature due to large spin-orbit interaction. A large Rashba spin-orbit coefficient on the order of 100 meV·Å is obtained through weak anti-localization measurements. An effective mass of 0.03me is determined from temperature-dependent magnetoresistance measurements. Josephson junctions fabricated with a contact separation of 200 nm exhibit products IcRN = 495 μV and IexRN = 2.0 mV of normal resistance RN, critical current Ic, and excess current Iex. |
Monday, March 4, 2024 8:24AM - 8:36AM |
A15.00003: Poor Man's Majoranas and 3-site chains in a QD-ABS system David van Driel, Nick van Loo, Francesco Zatelli, Bart Roovers, Alberto Bordin, Greg Mazur, Tom Dvir, Jan Cornelis Wolff, Guanzhong Wang, Leo P Kouwenhoven Because of their non-abelian exchange statistics, Majorana zero modes are highly promising candidates for topological quantum computing. While these quasiparticles have been predicted to arise in semiconducting nanowires coupled to superconductors, their experimental observation has proven to be quite elusive. In a different approach, the first physical implementation of a minimal Kitaev chain has recently demonstrated the ability to instead create so-called Poor Man's Majorana zero modes [1]. This is enabled via the coupling of two quantum dots via an Andreev Bound State in a short proximitized semiconductor. In this talk, we demonstrate that this state itself can also form one of the sites of a Kitaev chain and show that Poor Man's Majorana bound states arise in this coupled Andreev Bound State - quantum dot system [2]. Moreover, we introduce an auxiliary quantum dot to the system, whose coupling invokes a splitting of the zero energy modes. This splitting is an important metric to gauge the Majorana polarization of a Kitaev chain. The auxiliary quantum dot can also participate in the Kitaev chain when the coupling is tuned appropriately. This enables the creation of a three-site chain, forming an attractive approach to scale up the length of these artificial Kitaev chains and thereby increasing the robustness of the Majorana zero modes. |
Monday, March 4, 2024 8:36AM - 8:48AM |
A15.00004: Engineering Majorana bound states in coupled quantum dots in a two-dimensional electron gas Qingzhen Wang, Bas Ten Haaf, A. Mert Bozkurt, Chun-Xiao Liu, Ivan Kulesh, Philip Kim, Di Xiao, Candice Thomas, Michael J Manfra, Tom Dvir, Michael Wimmer, Srijit Goswami Majorana bound states (MBSs) can emerge in superconductor-semiconductor hybrids, by engineering artificial Kitaev chains. In this work, we realize a two-site Kitaev chain in a two-dimensional electron gas (2DEG) by coupling two quantum dots (QDs) through a region proximitized by a superconductor. We demonstrate systematic control over inter-dot couplings through in-plane rotations of the magnetic field and via electrostatic gating of the proximitized region.This allows us to tune the system to sweet spots in parameter space, where robust correlated zero bias conductance peaks are observed in tunnelling spectroscopy. By studying the evolution of the energy spectrum with magnetic field, we show that it is possible to experimentally distinguish between high and low Majorana polarization regimes, an important metric for Majorana-based qubits. The presented implementation of a Kitaev chain on a scalable and flexible 2D platform provides a realistic path towards more advanced experiments that require manipulation and readout of multiple MBSs. |
Monday, March 4, 2024 8:48AM - 9:00AM |
A15.00005: Charge sensing to probe the quasiparticle poisoning lifetime of an Andreev bound state Yining Zhang Quasiparticle poisoning causes dephasing in superconducting-semiconducting hybrid qubits, and the poisoning time could prove to be a limiting factor in the operation of such qubits. One way to extract these times is to perform fast charge/parity sensing measurements. Quantum dots have been widely used as sensors to read out the charge occupation of neighbouring quantum dots. Here we study a quantum dot coupled to an Andreev bound state (ABS), defined in an InSbAs/Al two-dimensional electron gas. We use radio frequency reflectometry to read out the charge state of the ABS. As the ABS goes through a singlet-doublet transition, we see clear shifts in the sensing dot signal. We show progress toward extracting quasiparticle poisoning lifetimes from such measurements. |
Monday, March 4, 2024 9:00AM - 9:12AM |
A15.00006: Spin properties of the chiral Andreev edge states Chun-Chia Chen, Jordan McCourt, John Chiles, Zubair Iftikhar, Lingfei Zhao, Kenji Watanabe, Takashi Taniguchi, Francois Amet, Gleb Finkelstein At the interfaces between a superconductor and a quantum Hall, the edge states are proximitized forming chiral Andreev edge states (CAES). The presence of CAES can be detected via non-local resistance measurements, where downstream of the superconducting contact either positive or negative can be measured, indicating primarily normal or Andreev reflections. In this abstract, we investigate the spin properties of the CAES. We use a local top gate to spatially separate the edge states to/from the superconductor into different spin-polarized channels, which allows us to explore the spin properties of the CAES signals. This study contributes to the understanding of spin-dependent Andreev reflections in the quantum Hall regime and sheds light on the interplay of CAES across different edge-state channels. |
Monday, March 4, 2024 9:12AM - 9:24AM |
A15.00007: Supercurrent through an Andreev trimer Alberto Bordin, Florian J Bennebroek Evertsz, Gorm O Steffensen, Tom Dvir, Grzegorz P Mazur, David van Driel, Nick van Loo, Guanzhong Wang, Francesco Zatelli, Jan Cornelis Wolff, Alfredo Levy Yeyati, Leo P Kouwenhoven Supercurrent through quantum dots embedded into hybrid superconductor–semiconductor–superconductor Josephson junctions has been widely investigated in the last two decades. However, previous studies were blind to the physics taking place below each superconducting lead. Here we realize a device with additional normal-metal tunneling probes, unveiling the Andreev bound states (ABSs) populating the spectrum underneath each superconductor. Such ABSs play a crucial role, that is essential for matching theory and experimental data. Furthermore, by varying the ABS chemical potentials with electrostatic gates, we show how to control the supercurrent through the quantum dot and, in particular, increase its maximum by up to two orders of magnitude. Finally, we show how a strong coupling between the ABSs and the quantum dot can create a three-site Andreev molecule. |
Monday, March 4, 2024 9:24AM - 9:36AM |
A15.00008: Non-local modulation of supercurrent in a quantum-dot Josephson junction coupled to a secondary quantum dot Francesco Zatelli, Guanzhong Wang, Thomas Van Caekenberghe, Alberto Bordin, Florian Bennebroek Evertsz, Chunxiao Liu, Greg Mazur, Nick van Loo, David van Driel, Jan Cornelis Wolff, Michael Wimmer, Tom Dvir, Leo P Kouwenhoven Quantum dot-superconductor arrays represent a promising platform for the realization of Kitaev chains [1,2]. Recently, a two-site Kitaev chain hosting poor man’s Majorana bound states has been demonstrated using two quantum dots coupled via a superconductor [3,4]. However, to achieve a robust topological phase it is necessary to increase the number of sites, thereby introducing multiple coupled quantum-dot Josephson junctions with non-trivial current-phase relations. In a quantum-dot Josephson junction, the phase of the ground state switches between 0 and π depending on the parity of the quantum dot [5]. However, its phase diagram is expected to be modified when coupled to another quantum dot [6]. Here, we use a hybrid InSb/Al nanowire to form a quantum-dot Josephson junction coupled to an additional quantum dot via elastic co-tunnelling and crossed Andreev reflection. We observe that the secondary dot has a strong non-local effect on the supercurrent, indicating a deviation from the usual 0-π transition. |
Monday, March 4, 2024 9:36AM - 9:48AM |
A15.00009: A three site Kitaev chain in InSb/Al nanowire hybrid. Grzegorz P Mazur, Alberto Bordin, Tom Dvir, Chunxiao Liu, Guanzhong Wang, Francesco Zatelli, Nick van Loo, Jan Cornelis Wolff, Michael Wimmer, Ghada Badawy, Sasa Gazibegovic, Erik P. A. M. Bakkers, Leo P Kouwenhoven Recent technological advancements in the fabrication of semiconductor/superconductor hybrid nanowire devices have enabled the experimental realization of a minimal Kitaev chain within a quantum dot (QD) – superconductor (SC) – quantum dot (QD) configuration[1]. Electrostatic control of crucial parameters, such as Crossed Andreev Reflection (CAR) and Elastic Co-Tunneling (ECT), allows for precise tuning of the system along the chain, providing a basis for scalable control [2]. I will present the experimental realization of a three-site Kitaev chain in a QD-SC-QD-SC-QD device. This scaling holds promise in terms of enhancing the protection of the zero modes within the system, surpassing that of a two-site chain. Additionally, I will explore the impact of the superconducting phase difference on the spectrum of the three-site chain. |
Monday, March 4, 2024 9:48AM - 10:00AM |
A15.00010: Flux control in a three-site Kitaev chain in coupled quantum dots Sebastiaan ten Haaf, Qingzhen Wang, Yining Zhang, Ivan Kulesh, Christian G Prosko, Di Xiao, Candice Thomas, Michael J Manfra, Srijit Goswami Majorana bounds states (MBSs) can be engineered in semiconductor-superconductor hybrids by realizing a Kitaev chain. We study a three-site Kitaev chain in a semiconductor two-dimensional electron gas, where we couple three QDs via two hybrid regions. In this configuration the control over the relative superconducting phase between the two hybrids becomes crucial, as a π-phase difference is expected to close the gap between MBSs and higher energy excitations. To address this, we drive a flux through a superconducting loop connecting the two hybrid regions and study the dependence of the density of states through tunnelling spectroscopy measurements at all three QD sites. The study provides important insights for controlling longer Kitaev chains, providing a step forward towards integrating robust MBS-based qubits. |
Monday, March 4, 2024 10:00AM - 10:12AM |
A15.00011: YSR Bond Qubit in a Double Quantum Dot with cQED Operation Gorm O Steffensen, Alfredo Levy Yeyati Connecting two half-filled quantum dots to two superconducting leads induce a competetion of bonds, with the dots either forming an interdot exchange bond, or individual YSR screening bonds with the leads. Defining a qubit using these singlet parity bonding states yields both dot charge noise protection, due to the chargeless nature of the screening quasiparticles, and magnetic noise protection, as bonds protect against magnetic polarization. In this talk I propose to embed a DQD Josephson junction in parallel with a transmon to facilitate full cQED measurements and operation of a YSR bond qubit. I show that for realistic parameters two-tone spectroscopy of the DQD can be performed, and that a significant parameter regime is available for qubit operation. In addition, coherent manipulations of the bond states can be done via dot gates, and single-shot readout by measurements of a capacitively coupled resonator. Lastly, I show that gate noise on couplings are probably the primary source of qubit decoherence. As this qubit is protected against nuclear Overhauser fields and does not rely on spin-orbit interactions for operation a wider range of material platforms is available compared to current Andreev spin qubits, while qubit operations, measurement, and intialization can still be performed via cQED techniques. |
Monday, March 4, 2024 10:12AM - 10:24AM |
A15.00012: Robust 1D proximity supercondcutivity along graphene domain walls in quantizing fields Julien Barrier, Na Xin, Minsoo Kim, Roshan Krishna Kumar, Piranavan Kumaravadivel, Lee Hague, Alexey Berdyugin, Christian Moulsdale, Vladimir Enaldiev, Irina Grigorieva, Leonid Glazman, Jonathan R Prance, Vladimir Falko, Andre K Geim Extensive efforts have been undertaken to combine superconductivity and the quantum Hall effect so that Cooper-pair transport between superconducting electrodes in Josephson junctions is mediated by quantized edge states. This interest is currently motivated mainly by the prospect of creating topologically-protected quasiparticles but also extends into metrology and device applications. So far, it has proven challenging to achieve detectable supercurrents through quantum Hall conductors. Here we show that domain walls in minimally twisted bilayer graphene support robust proximity superconductivity in quantizing fields, allowing junctions with steady (non-oscillatory) critical currents over a several Tesla range approaching the upper critical field. The supercurrent is limited only by the quantum conductance of ballistic 1D channels residing inside the walls. Our findings offer an interesting avenue for exploring both fundamental physics and device applications. |
Monday, March 4, 2024 10:24AM - 10:36AM |
A15.00013: Topological Andreev bands in three-terminal graphene Josephson junctions Woochan Jung, Seyoung Jin, Sein Park, Takashi Taniguchi, Kenji Watanabe, Gil Young Cho, Gil-Ho Lee Multiply connected electronic networks threaded by flux tubes was proposed as a potential platform for studying adiabatic quantum transport properties, which are closely linked to topological invariants [1]. This concept could be realized in multi-terminal Josephson junctions (MTJJs) [2]. However, manifestations of topology in MTJJs are still an open case of experimental study. |
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