I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
08
Okt
2026
Quantitative Rules for Parallel Calibration and Drift-Resilient Maintenance of Large-Scale Superconducting Quantum Processors
As superconducting quantum processors scale toward hundreds of qubits, manual calibration becomes increasingly costly and difficult to sustain. Here we address two system-level factors
governing automated calibration, namely, crosstalk induced by parallel operations and temporal drift of control parameters. On a 66-qubit superconducting processor, cross-entropy benchmarking shows that single-qubit calibration tolerates full-chip concurrency with minimal fidelity loss, whereas CZ calibration requires a minimum coupler-graph distance of four to avoid elevated control errors. Continuous monitoring of representative qubit and coupler parameters further yields quantitative refresh rules that assign refresh priority by error-budget consumption. These results turn two conventionally heuristic choices, the concurrency density of calibration tasks and the refresh priority of each control parameter, into measurable operating rules. Implemented within an automated calibration framework, the rules support a six-qubit Greenberger-Horne-Zeilinger state with a zero-noise-extrapolated fidelity of 89.64%, distance-dependent logical-error suppression in a single-cycle repetition-code benchmark, and a reduction of the mean single-qubit error from 0.023 to 0.011 on a 337-qubit processor, providing an experimentally grounded reference for the automated calibration and maintenance of current and future large-scale superconducting quantum systems.
A quasiparticle-protected superconducting qubit
Superconducting quantum circuits underpin large-scale quantum processors and are increasingly interfaced with optical systems, yet they are vulnerable to quasiparticle poisoning from
high-energy radiation and optical fields. Gap engineering of Josephson junctions suppresses quasiparticle-induced relaxation, but quasiparticles near the junction can still shift the qubit frequency and cause phase errors. Here, we extend gap engineering beyond the junction using a flux-tunable transmon with a gold-on-niobium ground plane and island and strongly gap-engineered aluminum junctions designed to keep quasiparticles away from the junction leads. Compared with an all-aluminum transmon with nominally identical junctions, we demonstrate that the niobium device withstands more than an order of magnitude higher near-infrared optical power before excess relaxation appears. The Nb transmon shows no resolvable quasiparticle-induced frequency shift over the same power range. At the same time, we observe that dephasing and state-preparation-and-measurement infidelity increase with optical power even while relaxation remains protected. These results suggest that engineering the quasiparticle energy landscape beyond the junction can substantially increase qubit resilience, not only to radiation-induced error bursts, but also to nearby optical fields.
Quantum Simulation of a Hyperbolically Driven Quantum System with Superconducting Circuits
Hyperbolic geometry hosts a plethora of exotic quantum phenomena ranging from holographic duality to novel topological phases. However, investigating these effects experimentally remains
challenging due to the Euclidean constraints of natural crystalline materials. While recent synthetic lattices have achieved static realizations, they often lack the dynamical tunability required to explore the full geometric landscape. Here, we overcome these limitations by implementing a quantum simulation of hyperbolic geometry within the parameter space of a superconducting quantum circuit. We construct a Hyperbolically Driven Quantum System (HDQS) by mapping the hyperbolic properties onto the dynamically controllable Hamiltonian parameters. By probing the systems‘ response under geometric quantum driving, we elucidate how the intrinsic geometry of the parameter space dictates observable physical quantities. Furthermore, we extend the theoretical framework to realize ensemble simulation. This generalization enables us to harness the fast coherent control of superconducting qubits to capture essential geometric characteristics, establishing a versatile platform for exploring quantum dynamics on hyperbolic manifolds.
Sub-MHz SWAP spectroscopy of two-level systems in superconducting qubits
An outstanding challenge in superconducting quantum circuits is mitigating loss from two-level system (TLS) defects. SWAP spectroscopy with flux-tunable qubits can detect individual
TLSs, but the Rabi chevrons that signal coherent exchange have been observed only for the most strongly coupled defects. Here, we introduce a sequence with fast flux pulses only at state preparation and readout, switched off during the energy-relaxation delay for finer frequency resolution and longer interaction times. We detect Rabi chevrons at swap rates as low as 0.1 MHz, an order of magnitude lower than previously reported. In the dressed-state picture, we fit the coherent swap oscillations to extract the TLS energy-relaxation time. These Rabi chevrons reveal coherent TLSs with a median energy-relaxation time of 10 microseconds, at coupling strengths previously associated with incoherent TLSs. The swap coherence times exceed the qubit T2* limited by flux noise, indicating that the dressed gap protects them from low-frequency 1/f noise.
07
Okt
2026
Geodesic-based optimal control for leakage suppression in superconducting qubits
Superconducting qubits are often based on the first two energy levels of a physical anharmonic LC oscillator. Since the anharmonicity of such systems is usually much lower than the
involved energy gaps, population can easily leak to higher energy states. This is what characterizes leakage errors, and it can have multiple sources: from coherent error induced by the control platform to incoherent thermal dissipation. In this work, we adapt an optimal control method based on sub-Riemannian geodesic search in the unitary group for a system consisting of two superconducting qubits with leakage levels. We use the Rx(π/2) rotation for single-qubit operation analysis, and the iSWAP operation for two-qubit analysis. For the former, we find considerable performance improvement in average gate fidelity as well as in the reduction of leakage errors when comparing the obtained optimal pulses with Gaussian and DRAG pulses, especially for short duration pulses. For the iSWAP gate, although leakage error remains roughly the same, we manage to obtain considerably higher fidelities with the cost of requiring a slightly longer time evolution.
Stimulated emission for a three-level artificial atom in waveguide quantum electrodynamics
This work is devoted to a theoretical study of the interaction of a quantum three-level ladder system with a continuous electromagnetic field in a one-dimensional open waveguide. Weconsider a situation closely resembling stimulated emission – the scattering of a single-photon exponential pulse by an excited three-level emitter. Using the real-space formalism, we obtain an analytical expression for the wavefunction of our system. We show that, for the low anharmonicity of a three-level system inherent to a transmon (the most common type of artificial atom), the influence of the third level can have a significant effect on the system’s behavior. Namely, the presence of the third level largely suppresses the stimulated emission effect if the relative anharmonicity is lower than |αr|<4%. However, for a three-level system, it is possible to obtain correlation effects such as photon bunching in the reflected field, which can also be 'switched off' by tuning the incident photon parameters.[/expand]
Dynamically protected erasure qubit via low-frequency charge driving
Dynamical protection via strong driving can enable resilient quantum processing on imperfect physical hardware. However, the practical utility of such schemes is frequently limited
by parasitic processes such as drive-induced dephasing and leakage. Here, we demonstrate that sub-GHz charge driving of superconducting Kerr oscillators (KOs) in the transmon regime circumvents this trade-off, simultaneously activating fast parametric interactions and protecting the encoded qubit from low-frequency noise. The key is the frequency dependence of the charge sensitivity: using the AC Stark shift as a probe, we find that the KO frequency sensitivity to a charge drive grows quadratically with both drive frequency and amplitude, making the oscillator weakly sensitive to 1/f charge noise yet strongly coupled to drives near 1~GHz. Exploiting this, we first demonstrate cooling and reset of the KO in 82~ns, to a residual population below 0.7%—lower than its 2.5% steady-state thermal population. Next, using two KOs, we demonstrate logical control and dynamical protection of a dual-rail qubit with nearly fourfold erasure bias. Finally, using a single end-of-circuit erasure check, we achieve an error per Clifford of 5.6×10−4, which falls to 1.5×10−4 after post-selection, with 25~ns gates.
Nonlinear Feedback in Josephson Circuit Optimization: Application to a Kerr-Reversal JTWPA
Optimizing Josephson-based nonlinear microwave devices is computationally demanding because the straightforward approach requires exploring broad circuit parameter spaces through expensive
nonlinear simulations. Josephson Circuits Optimizer addresses this problem by using harmonic balance simulations in two stages: fast linear simulations to select promising circuit configurations according to properties such as impedance and phase matching, followed by nonlinear simulations to optimize their operating conditions. However, pump-induced effects such as impedance renormalization and Kerr-induced modifications of phase matching are not captured during the initial linear stage. We therefore introduce a nonlinear feedback extension that transfers information from the pumped response back to the linear optimization. The approach is investigated using a Josephson traveling-wave parametric amplifier with a reversed-Kerr architecture, whose model is validated against experimental gain measurements. We then evaluate the difference between the linear and pumped response values of a metric based on the input reflection coefficient, while excluding configurations with insufficient third-harmonic suppression. This discrepancy is considered a candidate feedback observable, as it exhibits features similar to the gain landscape, supporting its use in subsequent optimization cycles.
06
Okt
2026
Physical Design Automation for Planar Superconducting Quantum Chips
Superconducting circuits have emerged as one of the most promising and scalable platforms for quantum com- puting, with substantial industrial adoption driving qubit counts steadily
upward. Yet the layout of the corresponding chips is still primarily performed manually, consuming multiple days or weeks of expert effort, even for moderately sized designs. Existing automation approaches sidestep this bottleneck by simplifying the underlying problem and relaxing physical constraints. Therefore, they fall short of fabrication-ready results. To overcome this scalability wall without such compromises, we first introduce a formal abstraction that translates physical device characteristics into a rigorous geometric problem formulation. This abstraction bridges physical realization and design automation. Building upon this abstraction, we then propose a three-stage design automation flow comprising geometry-aware global partitioning, ILP-based port assignment, and a hierarchical routing pipeline. Evaluations conducted by our interdisciplinary team of design au- tomation researchers and superconducting hardware experts con- firm that the resulting flow produces complete, manufacturing- ready layouts that comply with the physical design rules at the push of a button. That is, it operates fully automatically within seconds to a few minutes, and solves complex instances up to 25x faster than the state of the art. All methods are released as the fully open-source tool mqt-scpd as part of the Munich Quantum Toolkit, providing the first readily usable, end- to-end design flow for planar superconducting quantum chips that explicitly addresses the underlying physical characteristics and requirements.
04
Okt
2026
Epitaxial NbN-junction-based self-shunted superconducting flux qubit with high anharmonicity
We report a demonstration of a self-shunted superconducting flux qubit (SSFQ) as an ultracompact, strongly anharmonic, and long-lifetime qubit by using the full epitaxially grown NbN/AlN/NbN
Josephson junctions. The NbN-junction-based SSFQ achieved a high anharmonicity of 797 MHz as well as drastically reduced footprint of the qubit compared to capacitively shunted (C-shunt) flux qubits with a large shunt capacitor. The lifetime of the SSFQ reached 13 – 25 μs, which is comparable to or relatively higher than that of NbN-based C-shunt flux qubits and Al-based flux qubits with more than 10 times smaller junctions. This indicates that the large epitaxial NbN-based junction can be adopted for SSFQ as well as merged-element transmon with the relatively large junctions. The results presented in this work will offer a new choice of the scalable qubits as well as the material platform toward the realization of large-scale superconducting quantum computers.