Probing defect densities at the edges and inside Josephson junctions of superconducting qubits

Abstract

Tunneling defects in disordered materials form spurious two-level systems which are a major source of decoherence for micro-fabricated quantum devices. For superconducting qubits, defects in tunnel barriers of submicrometer-sized Josephson junctions couple strongest to the qubit, which necessitates optimization of the junction fabrication to mitigate defect formation. Here, we investigate whether defects appear predominantly at the edges or deep within the amorphous tunnel barrier of a junction. For this, we compare defect densities in differently shaped Al/AlO${}_x$/Al Josephson junctions that are part of a Transmon qubit. We observe that the number of detectable junction-defects is proportional to the junction area, and does not significantly scale with the junction's circumference, which proposes that defects are evenly distributed inside the tunnel barrier. Moreover, we find very similar defect densities in thermally grown tunnel barriers that were formed either directly after the base electrode was deposited, or in a separate deposition step after removal of native oxide by Argon ion milling.

References in corpus (36)

• Charge insensitive qubit design derived from the Cooper pair box
• Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architecture
• Decoherence in Josephson Qubits from Dielectric Loss
• Coherent Josephson qubit suitable for scalable quantum integrated circuits
• 1/f noise: implications for solid-state quantum information
• Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
• Surface participation and dielectric loss in superconducting qubits
• Fluctuations of Energy-Relaxation Times in Superconducting Qubits
• Decoherence benchmarking of superconducting qubits
• Materials loss measurements using superconducting microwave resonators
• Observation of quantum oscillations between a Josephson phase qubit and a microscopic resonator using fast readout
• Implementation of low-loss superinductances for quantum circuits
• State tomography of capacitively shunted phase qubits with high fidelity
• Correlating decoherence in transmon qubits: Low frequency noise by single fluctuators
• Observation of directly interacting coherent two-level systems in a solid
• Electric field spectroscopy of material defects in transmon qubits
• Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits
• Characterization and Reduction of Capacitive Loss Induced by Sub-Micron Josephson Junction Fabrication in Superconducting Qubits
• Characterization and reduction of microfabrication-induced decoherence in superconducting quantum circuits
• Lifetime and Coherence of Two-Level Defects in a Josephson Junction
• Generalized Tunneling Model for TLS in amorphous materials and its predictions for their dephasing and the noise in superconducting microresonators
• Novel E-beam lithography technique for in-situ junction fabrication: the controlled undercut
• Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
• Direct identification of dilute surface spins on Al${}_2$O${}_3$: Origin of flux noise in quantum circuits
• Bulk and Surface Tunneling Hydrogen Defects in Alumina
• One- and two-photon spectroscopy of a flux qubit coupled to a microscopic defect
• Overlap junctions for high coherence superconducting qubits
• Anomalous avoided level crossings in a Cooper-pair box spectrum
• Probing individual tunneling fluctuators with coherently controlled tunneling systems
• Quantum Sensors for Microscopic Tunneling Systems
• Electronic Decoherence of Two-Level Systems in a Josephson Junction
• Multi-level Spectroscopy of Two-Level Systems Coupled to a dc SQUID Phase Qubit
• In-situ bandaged Josephson junctions for superconducting quantum processors
• Low temperature 1/f noise in microwave dielectric constant of amorphous dielectrics in Josephson qubits
• A Josephson junction defect spectrometer for measuring two-level systems
• An argon ion beam milling process for native ${\text{AlO}}_{\text{x}}$ layers enabling coherent superconducting contacts

Cited by in corpus (13)

• High-coherence superconducting qubits made using industry-standard, advanced semiconductor manufacturing
• Mitigation of frequency collisions in superconducting quantum processors
• In-situ bandaged Josephson junctions for superconducting quantum processors
• Enhancing the Coherence of Superconducting Quantum Bits with Electric Fields
• Identification of different types of high-frequency defects in superconducting qubits
• Alternating Bias Assisted Annealing of Amorphous Oxide Tunnel Junctions
• Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes
• The influence of pinholes and weak-points in aluminium-oxide Josephson junctions
• Low-Energy Backgrounds in Solid-State Phonon and Charge Detectors
• Strain-spectroscopy of strongly interacting defects in superconducting qubits
• In-situ scanning gate imaging of individual two-level material defects in live superconducting quantum circuits
• Robust gates with spin-locked superconducting qubits
• Why Superconducting Ta Qubits Have Fewer Tunneling Two-Level Systems at the Air-Oxide Interface Than Nb Qubits