Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W75: Superconducting Qubit Junction Dynamics and MaterialsFocus
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Sponsoring Units: DQI Chair: Loren Alegria, Lawrence Livermore Natl Lab Room: Room 401/402 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W75.00001: Circuit quantum electrodynamics measurement of Andreev levels in a semiconducting nanowire weak link Invited Speaker: Pavel Kurilovich Andreev levels are supercurrent-carrying fermionic modes responsible for the manifestation of the Josephson effect in superconducting weak links. Individual Andreev levels can be resolved in highly transparent, few-channel weak links by embedding them in superconducting microwave resonators. We apply such circuit quantum electrodynamics probing method to measure Andreev levels in a semiconducting nanowire proximitized by superconducting electrodes. We experimentally show that this mesoscopic system reproduces the hallmark phenomena of atomic physics: from radiation-induced transitions between the discrete levels to Coulomb repulsion between the quasiparticles. We also uncover phenomena with no direct analogues in atomic physics. They arise from the interplay between strong spin-orbit interaction and superconductivity. Among them are the “zero-field” spin splitting and the presence of supercurrent sensitive to the quasiparticle spin. The latter effects allow us to coherently control the spin of a superconducting quasiparticle [1]. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W75.00002: Measuring Quasi-particle Tunneling Rates in Transmon Qubits Yi-Hsiang Huang, Yizhou Huang, Zachary Steffen, Haozhi Wang, Kungang Li, Sudeep K Dutta, Frederick C Wellstood, Benjamin S Palmer The tunneling of non-equilibrium quasiparticles (QPs) across the Josephson junction of superconducting qubits is a source of energy loss and dephasing, resulting in a reduced coherence time. To measure changes in the charge parity rate between the two pads of a transmon qubit, we have designed transmons with a charge dispersion approximately 6 MHz between the first excited |e> and the second excited states |f>. The designed transmons allow fast mapping of the charge parity rate while maintaining a good charge-noise protection between the |g> and |e> states. Using a modified Ramsey pulse sequence on the |e> to |f> states, we monitor temporally the effective charge parity of the qubits. For some Al qubits, we compare the measured charge parity rates to T1 with and without a direct galvanic connection to the ground plane. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W75.00003: Suppression of quasiparticle poisoning in transmon qubits by gap engineering Plamen Kamenov, Thomas J DiNapoli, Jordan Huang, Srivatsan Chakram, Michael Gershenson Performance of several types of superconducting devices operating at ultra-low temperatures is impaired by the presence of non-equilibrium quasiparticles (QP). In particular, inelastic QP tunneling across the Josephson junctions in superconducting qubits impedes the realization of quantum error correction. Here we use the so-called gap engineering to suppress tunneling of low-energy quasiparticles in Al-based transmon qubits, a leading platform for multi-qubit circuits. By implementing potential barriers for QP, we suppressed QP tunneling across the junction and preserved charge parity for well over 103 seconds. Suppression of QP tunneling results in reduction of the qubit energy relaxation and dephasing rates. The demonstrated approach to gap engineering can be easily implemented in all circuits with Al-based Josephson junctions. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W75.00004: Improved Coherence in Optically Defined Niobium Tri-layer Josephson Junction Qubits Alexander V Anferov, Kan-Heng Lee, Shannon Harvey, David Schuster While higher-critical-temperature Josephson junctions have been widely replaced by low-loss aluminum junctions for sensitive quantum circuitry, aluminum-based quantum circuits are still limited by quasiparticles to operation at temperatures below 0.1 Kelvin due to their low superconducting temperature. With significant recent interest in the exploration of diverse materials that can push these boundaries, we revisit niobium tri-layer junctions as the core components in qubits. Combining recent tri-layer junction advancements including sidewall-passivating spacer structures, heat annealed barriers and selective etching to reduce dielectric material, we apply material advancements from modern superconducting qubits to fabricate all-niobium transmons using only optical lithography. We characterize devices at various frequencies in the microwave range, measuring coherence times corresponding to qubit quality factors above 105: much higher than previously demonstrated with niobium junctions, and much closer to the loss rates seen in conventional aluminum junction qubits. We find that the higher superconducting gap energy also results in reduced quasiparticle sensitivity around 0.1 – 0.2 K, where aluminum junction performance starts to deteriorate. This low-loss junction process is readily applied to standard niobium optical-based foundry processes, opening new pathways for integration and scalability, and paves the way for higher temperature and higher frequency quantum devices. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W75.00005: Fabrication of uniform Manhattan-style transmon qubits on 150 mm wafers Liuqi Yu, Wei Liu, Lan-Hsuan Lee, Anton Komlev, Kunal Mitra, Seung-Goo Kim, Alexander Plyushch, Hasnain Ahmad, Mario Palma, Grégoire Coiffard, Lily Yang, Tianyi Li To scale up the number of qubits patterned onto a single wafer, the quantum processor rapidly increases in its footprint. To maintain the processor’s performance, a precise control over the frequencies of individual qubits is often of great importance. Highly coherent transmon qubits can be fabricated through angled depositions. The qubit frequency is directly associated with room temperature Josephson junction (JJ) resistance via Ambegaokar–Baratoff relation. When fabricating on large-scale wafer, since the evaporation source is point-like, the effective deposition angles are different for individual JJs depending on their positions on the wafer. It inevitably leads to varying JJ resistances even for the same designed JJ size. Consequently, it presents a challenging task to accurately allocate design qubit frequencies on a large-scale wafer. In this work, we fabricate identical Manhattan-style JJs across a 150 mm wafer to examine the spatial uniformity of their resistances. To compensate the variation of the deposition angle, the designed JJ sizes are individually adjusted according to their positions on the wafer. The room temperature resistance measurements show a variation in the resistance of about 10% across the wafer. The uniformity is further improved by local annealing of individual JJs post fabrication. The resultant standard deviation of the resistance is reduced to less than 1% of the average JJ resistance, which is suitable for large scale qubit production. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W75.00006: Van der Waals semiconductors as Josephson junction barriers for superconducting qubits Jesse Balgley, Abhinandan Antony, Xuanjing Chu, Ethan G Arnault, Martin V Gustafsson, James C Hone, Kin Chung Fong Two-dimensional van der Waals (vdW) materials are promising platforms for superconducting quantum devices due to their single-crystallinity, low defect density, and lack of dangling bonds. vdW semiconductors—whose band gaps are typically ~5x smaller than in vdW insulators like hBN—can exhibit tunneling through ~10 layers, enabling large-area, homogeneous Josephson junctions with greater participation ratios in ultra-clean vdW interfaces. We characterize the dc and microwave electronic properties of vdW Josephson junctions with ultra-high-purity WSe2 semiconductor barriers and discuss their potential as components for small-footprint, high-quality-factor superconducting qubits. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W75.00007: Development of transmon qubit with Sn based hybrid superconductor-semiconductor nanowire josephson junction with electrostatic gate control Amrita Purkayastha, Param J Patel, Azarin Zarassi, Amritesh Sharma, Mihir Pendharkar, Connor P Dempsey, Kun Zuo, Chris J Palmstrom, Michael J Hatridge, Sergey M Frolov Qubits with hybrid superconducting-semiconducting nanowires have garnered considerable interest since their first demonstration with Aluminum (Al) based gatemons. Tin (Sn) based hybrid superconductor-semiconductor nanowire josephson junctions show promise in further developing this electrostatic gate tunable transmon qubit platform with its larger induced superconducting gap [1] and high magnetic field compatibility [1] compared to Al. In this work we present our experimental progress on developing electrostatic gate tunable transmon qubit with these Sn based hybrid nanowire Josephson Junctions. With spectroscopic and time domain measurements we report on their performance in terms of coherence and gate tunable anharmonicity. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W75.00008: Mitigation of frequency collisions in scalable superconducting quantum processors Amr Osman, Jorge Fernández-Pendás, Sandoko Kosen, Marco Scigliuzzo, Giovanna Tancredi, Christopher Warren, Anton Frisk Kockum, Jonas Bylander, Anita F Roudsari Qubit frequency predictability is a challenge for scalable quantum processors, where cross-talk imposes hard limits on the frequency separation between qubits. Qubit frequency uncertainties arise from the fabrication process and are attributed to deviations in the Josephson junction area and tunnel barrier thickness. In this work, we demonstrate more than two-fold improvement in qubit frequency reproducibility, compared to our previous baseline, by making larger tunnel junctions and achieve ~40 MHz standard deviation in frequency. We further study the implications of this on qubit lifetime and frequency crowding on quantum processors based on the parametric-gate architecture. While qubits fabricated using the larger tunnel junctions maintained similar coherence to our baseline, the anticipated yield of collision-free chips on a quantum processor improves significantly. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W75.00009: Investigating the impact of air-bridge and Josephson-junction fabrication order on transmon performance in circuit QED Matvey Finkel, Hendrik Martijn Veen, Sean van der Meer, Santiago Valles-Sanclemente, Leonardo DiCarlo Free-standing air bridges are key components of superconducting quantum processors. They are used to suppress odd modes of propagation in the coplanar-waveguide transmission lines of resonators and control lines, as well as to create cross-overs where transmission lines unavoidably intersect. Conventionally, air bridges are fabricated after the Josephson junctions of qubits, subjecting the junctions to more fabrication steps than strictly necessary (resist layers, lithography, temperature variations, etc.). Therefore, it may be advantageous to fabricate the qubit Josephson junctions last in order to minimize the impact of fabrication steps on the yield, coherence, and frequency targeting of superconducting qubits. We present an investigation of the impact of changing fabrication order on transmon performance metrics. |
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