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
21
Mai
2025
Search for Dark Photon Dark Matter of a Mass around 36.1 μeV Using a Frequency-tunable Cavity Controlled through a Coupled Superconducting Qubit
We report the results of a search for dark photon dark matter using a cavity that employs a transmon qubit as a frequency tuning component. The tuning mechanism utilizes the energy
level shift (Lamb shift) arising from the mode mixing between the qubit and the cavity mode. This method offers several advantages: (i) it does not introduce physical thermal noise from the tuning mechanism itself, (ii) it avoids electromagnetic leakage typically associated with cavity seams, and (iii) its implementation is straightforward. We excluded the dark photon parameter region for a dark photon mass around 36.1 μeVwith a peak sensitivity of χ∼10−12 over the mass range [36.0791,36.1765] μeV, surpassing the existing cosmological bounds.
Mitigating cosmic ray-like correlated events with a modular quantum processor
Quantum processors based on superconducting qubits are being scaled to larger qubit numbers, enabling the implementation of small-scale quantum error correction codes. However, catastrophic
chip-scale correlated errors have been observed in these processors, attributed to e.g. cosmic ray impacts, which challenge conventional error-correction codes such as the surface code. These events are characterized by a temporary but pronounced suppression of the qubit energy relaxation times. Here, we explore the potential for modular quantum computing architectures to mitigate such correlated energy decay events. We measure cosmic ray-like events in a quantum processor comprising a motherboard and two flip-chip bonded daughterboard modules, each module containing two superconducting qubits. We monitor the appearance of correlated qubit decay events within a single module and across the physically separated modules. We find that while decay events within one module are strongly correlated (over 85%), events in separate modules only display ∼2% correlations. We also report coincident decay events in the motherboard and in either of the two daughterboard modules, providing further insight into the nature of these decay events. These results suggest that modular architectures, combined with bespoke error correction codes, offer a promising approach for protecting future quantum processors from chip-scale correlated errors.
20
Mai
2025
An engineering guide to superconducting quantum circuit shielding
In this review, we provide a practical guide on protection of superconducting quantum circuits from broadband electromagnetic and infrared-radiation noise by using cryogenic shielding
and filtering of microwave lines. Recently, superconducting multi-qubit processors demonstrated quantum supremacy and quantum error correction below the surface code threshold. However, the decoherence-induced loss of quantum information still remains a challenge for more than 100 qubit quantum computing. Here, we review the key aspects of superconducting quantum circuits protection from stray electromagnetic fields and infrared radiation, namely, multilayer shielding design, materials, filtering of the fridge lines and attenuation, cryogenic setup configurations, and methods for shielding efficiency evaluation developed over the last 10 years. In summary, we make recommendations for creation of an efficient and compact shielding system as well as microwave filtering for a large-scale superconducting quantum systems.
19
Mai
2025
Josephson Junctions in the Age of Quantum Discovery
The unique combination of energy conservation and nonlinear behavior exhibited by Josephson junctions has driven transformative advances in modern quantum technologies based on superconducting
circuits. These superconducting devices underpin essential developments across quantum computing, quantum sensing, and quantum communication and open pathways to innovative applications in nonreciprocal electronics. These developments are enabled by recent breakthroughs in nanofabrication and characterization methodologies, substantially enhancing device performance and scalability. The resulting innovations reshape our understanding of quantum systems and enable practical applications. This perspective explores the foundational role of Josephson junctions research in propelling quantum technologies forward. We underscore the critical importance of synergistic progress in material science, device characterization, and nanofabrication to catalyze the next wave of breakthroughs and accelerate the transition from fundamental discoveries to industrial-scale quantum utilities. Drawing parallels with the transformative impact of transistor-based integrated circuits during the Information Age, we envision Josephson junction-based circuits as central to driving a similar revolution in the emerging Quantum Age.
15
Mai
2025
Light-Matter Interaction in dispersive Superconducting Circuit QED
It is well known that superconducting waveguides strongly attenuate the propagation of electromagnetic waves with frequencies beyond the superconducting gap. In circuit QED, the interaction
between non-linear charge qubits and superconducting resonators invariably involves the qubit coupling to a large set of resonator modes. So far, strong dispersion effects near and beyond the superconducting-gap have been ignored in quantization models. Rather, it is assumed that the superconducting resonator behaves ideally across the large frequency intervals. We present a quantization approach which includes the superconducting frequency-dependent surface impedance and demonstrate that superconducting dispersion plays a role in determining the effective light-matter interaction cut-off.
13
Mai
2025
Simultaneous sweet-spot locking of gradiometric fluxonium qubits
Efforts to scale up superconducting processors that employ flux-qubits face numerous challenges, among which is the crosstalk created by neighboring flux lines, which are necessary
to bias the qubits at the zero-field and Φ0/2 sweet spots. A solution to this problem is to use symmetric gradiometric loops, which incorporate a flux locking mechanism that, once a fluxon is trapped during cooldown, holds the device at the sweet spot and limits the need for active biasing. We demonstrate this technique by simultaneously locking multiple gradiometric fluxonium qubits in which an aluminum loop retains the trapped fluxon indefinitely. By compensating the inductive asymmetry between the two loops of the design, we are able to lock the effective flux-bias within Φeff=−3×10−4Φ0 from the target, corresponding to only 15 % degradation in T2,E when operated in zero external field. The design strategy demonstrated here reduces integration complexity for flux qubits by minimizing cross-talk and potentially eliminating the need for local flux bias.
High-contrast interaction between remote superconducting qubits mediated by multimode cable coupling
Superconducting quantum processors offer a promising path towards practical quantum computing. However, building a fault-tolerant quantum computer with millions of superconducting qubits
is hindered by wiring density, packaging constraints and fabrication yield. Interconnecting medium-scale processors via low-loss superconducting links provides a promising alternative. Yet, achieving high-fidelity two-qubit gates across such channels remains difficult. Here, we show that a multimode coaxial cable can mediate high-contrast interaction between spatially separated super-conducting qubits. Leveraging interference between cable modes, we can implement high-fidelity controlled-Z and ZZ-free iSWAP gates by simply modulating qubit frequencies. Numerical simulations under realistic coherence and coupling parameters predict fidelities above 99% for both gate schemes. Our approach provides a versatile building block for modular superconducting architectures and facilitates distributed quantum error correction and large-scale fault-tolerant quantum computing.
CMOS-Compatible, Wafer-Scale Processed Superconducting Qubits Exceeding Energy Relaxation Times of 200us
We present the results of an industry-grade fabrication of superconducting qubits on 200 mm wafers utilizing CMOS-established processing methods. By automated waferprober resistance
measurements at room temperature, we demonstrate a Josephson junction fabrication yield of 99.7% (shorts and opens) across more than 10000 junctions and a qubit frequency prediction accuracy of 1.6%. In cryogenic characterization, we provide statistical results regarding energy relaxation times of the qubits with a median T1 of up to 100 us and individual devices consistently approaching 200 us in long-term measurements. This represents the best performance reported so far for superconducting qubits fabricated by industry-grade, wafer-level subtractive processes.
12
Mai
2025
Recovery dynamics of a gap-engineered transmon after a quasiparticle burst
Ionizing radiation impacts create bursts of quasiparticle density in superconducting qubits. These bursts severely degrade qubit coherence for a prolonged period of time and can be
detrimental for quantum error correction. Here, we experimentally resolve quasiparticle bursts in 3D gap-engineered transmon qubits by continuously monitoring qubit transitions. Gap engineering allowed us to reduce the burst detection rate by a factor of a few. This modest reduction falls several orders of magnitude short of the reduction expected if the quasiparticles quickly thermalize to the cryostat temperature. We associate the limited effect of gap engineering with the slow thermalization of the phonons in our chips after the burst.
10
Mai
2025
Protected Symmetrical Superconducting Qubit Based on Quantum Flux Parametron
Conventional Quantum Flux Parametrons (QFPs) have historically been used for storing classical bits in Josephson junction-based computers. In this work, we propose a novel QFP-based
topology dubbed „Degenerium“ qubit, to process and compute quantum information. Degenerium combines principles from the 0-π qubit and flux qubit to create ideally degenerate quantum ground states, while significantly simplifying the 0-π qubit structure. The symmetrical design of Degenerium enables easier qubit control and fabrication. We demonstrate that due to the inherent symmetry of Degenerium, our designed qubit is insensitive to fabrication-induced variations in critical current (Ic) of the Josephson junctions. Our calculations of depolarization and dephasing rates due to charge, flux, and critical current noise sources result in depolarization and dephasing times of 1.25 s and 90 μs, respectively. Further parameter tuning and optimization is possible to meet specific application demands.