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
10
Mä
2025
Fabrication and characterization of vacuum-gap microstrip resonators
In traveling-wave parametric amplifiers (TWPAs) low-loss capacitors are necessary to provide 50 Ω impedance matching to the increased inductance that is brought in by the nonlinear
elements used for amplification, be it Josephson junctions or high kinetic inductance materials. Here we report on the development of a fabrication process for vacuum-gap microstrips, a design in which the ground plane is suspended in close proximity above the center conductor without the support of a dielectric. In addition to high-capacitance transmission lines, this architecture also enables air-bridges and compact parallel-plate capacitors. The performance of the fabrication is examined using distributed aluminum and granular aluminum resonators in a cryogenic dilution refrigerator setup, showing quality factors on par with the fabrication processes used in state-of-the-art TWPAs. In addition to characterizing the dependence of the quality factors on power, also their behavior with respect to temperature is explored, applying a model based on thermal quasi-particles and saturable two-level systems (TLS), showing that the quality factors of the resonators are limited by TLS.
Josephson traveling-wave parametric amplifier based on low-intrinsic-loss coplanar lumped-element waveguide
We present a Josephson traveling-wave parametric amplifier (JTWPA) based on a low-loss coplanar lumped-element waveguide architecture. By employing open-stub capacitors and Manhattan-pattern
junctions, our device achieves an insertion loss below 1 dB up to 12 GHz. We introduce windowed sinusoidal modulation for phase matching, demonstrating that smooth impedance transitions effectively suppress intrinsic gain ripples. Using Tukey-windowed modulation with 8 % impedance variation, we achieve 20−23-dB gain over 5-GHz bandwidth under ideal matching conditions. In a more practical circuit having impedance mismatches, the device maintains 17−20-dB gain over 4.8-GHz bandwidth with an added noise of 0.13 quanta above standard quantum limit at 20-dB gain and −99-dBm saturation power, while featuring zero to negative backward gain below the bandgap frequency.
09
Mä
2025
Multifunctional Nonreciprocal Quantum Device Based on Superconducting Quantum Circuit
Nonreciprocal devices, such as isolator or circulator, are crucial for information routing and processing in quantum networks. Traditional nonreciprocal devices, which rely on the application
of bias magnetic fields to break time-reversal symmetry and Lorentz reciprocity, tend to be bulky and require strong static magnetic fields. This makes them challenging to implement in highly integrated large-scale quantum networks. Therefore, we design a multifunctional nonreciprocal quantum device based on the integration and tunable interaction of superconducting quantum circuit. This device can switch between two-port isolator, three-port symmetric circulator, and antisymmetric circulator under the control of external magnetic flux. Furthermore, both isolator and circulator can achieve nearly perfect unidirectional signal transmission. We believe that this scalable and integrable nonreciprocal device could provide new insight for the development of large-scale quantum networks.
07
Mä
2025
Generation of Frequency-Tunable Shaped Single Microwave Photons Using a Fixed-Frequency Superconducting Qubit
Scaling up a superconducting quantum computer will likely require quantum communication between remote chips, which can be implemented using an itinerant microwave photon in a transmission
line. To realize high-fidelity communication, it is essential to control the frequency and temporal shape of the microwave photon. In this work, we demonstrate the generation of frequency-tunable shaped microwave photons without resorting to any frequency-tunable circuit element. We develop a framework which treats a microwave resonator as a band-pass filter mediating the interaction between a superconducting qubit and the modes in the transmission line. This interpretation allows us to stimulate the photon emission by an off-resonant drive signal. We characterize how the frequency and temporal shape of the generated photon depends on the frequency and amplitude of the drive signal. By modulating the drive amplitude and frequency, we achieve a frequency tunability of 40 MHz while maintaining the photon mode shape this http URL measurements of the quadrature amplitudes of the emitted photons, we demonstrate consistently high state and process fidelities around 95\% across the tunable frequency range. Our hardware-efficient approach eliminates the need for additional biasing lines typically required for frequency tuning, offering a simplified architecture for scalable quantum communication.
Spectrum analysis with parametrically modulated transmon qubits
Exploring the noise spectrum impacting a qubit and extending its coherence duration are fundamental components of quantum technologies. In this study, we introduce parametric spectroscopy,
a method that merges parametric modulation of a qubit’s energy gap with dynamical decoupling sequences. The parametric modulation provides high sensitivity to extensive regions of the noise spectrum, while dynamical decoupling reduces the effect of driving noise. Our theoretical study shows that parametric spectroscopy enables access to the difficult high-frequency domain of the flux spectrum in transmons.
27
Feb
2025
Low crosstalk modular flip-chip architecture for coupled superconducting qubits
We present a flip-chip architecture for an array of coupled superconducting qubits, in which circuit components reside inside individual microwave enclosures. In contrast to other flip-chip
approaches, the qubit chips in our architecture are electrically floating, which guarantees a simple, fully modular assembly of capacitively coupled circuit components such as qubit, control, and coupling structures, as well as reduced crosstalk between the components. We validate the concept with a chain of three nearest neighbor coupled generalized flux qubits in which the center qubit acts as a frequency-tunable coupler. Using this coupler, we demonstrate a transverse coupling on/off ratio ≈ 50, zz-crosstalk ≈ 0.7 kHz between resonant qubits and isolation between the qubit enclosures > 60 dB.
Experimental realization of a quantum heat engine based on dissipation-engineered superconducting circuits
Quantum heat engines (QHEs) have attracted long-standing scientific interest, especially inspired by considerations of the interplay between heat and work with the quantization of energy
levels, quantum superposition, and entanglement. Operating QHEs calls for effective control of the thermal reservoirs and the eigenenergies of the quantum working medium of the engine. Although superconducting circuits enable accurate engineering of controlled quantum systems, beneficial in quantum computing, this framework has not yet been employed to experimentally realize a cyclic QHE. Here, we experimentally demonstrate a quantum heat engine based on superconducting circuits, using a single-junction quantum-circuit refrigerator (QCR) as a two-way tunable heat reservoir coupled to a flux-tunable transmon qubit acting as the working medium of the engine. We implement a quantum Otto cycle by a tailored drive on the QCR to sequentially induce cooling and heating, interleaved with flux ramps that control the qubit frequency. Utilizing single-shot qubit readout, we monitor the evolution of the qubit state during several cycles of the heat engine and measure positive output powers and efficiencies that agree with our simulations of the quantum evolution. Our results verify theoretical models on the thermodynamics of quantum heat engines and advance the control of dissipation-engineered thermal environments. These proof-of-concept results pave the way for explorations on possible advantages of QHEs with respect to classical heat engines.
Digital Simulation of Non-Abelian Parafermions in Superconducting Circuits
Parafermions, which can be viewed as a fractionalized version of Majorana modes, exhibit non-Abelian statistics and emerge in topologically ordered systems, while their realization
in experiment has been challenging. Here we propose an experimental scheme for the digital simulation of parafermions and their non-Abelian braiding in superconducting circuits by realizing the ℤd plaquette model on a two-dimensional lattice. Two protocols using quantum circuits and non-destructive measurements are introduced to prepare the ground state, on which the parafermion pairs are created by engineering dislocations. We further develop a generalized code deformation approach to realize the fusion and non-Abelian braiding statistics of parafermion modes, in which the concrete example for d=3 parafermions is studied in detail. We also examine the real parameter regime to confirm the feasibility in superconducting devices. This work extends previous methods for twist defects in superconducting qubits to qudit systems, and may open up a way for parafermion-based high-dimensional topological quantum computing with experimental feasibility.
26
Feb
2025
Scalable Low-overhead Superconducting Non-local Coupler with Exponentially Enhanced Connectivity
Quantum error correction codes with non-local connections such as quantum low-density parity-check (qLDPC) incur lower overhead and outperform surface codes on large-scale devices.
These codes are not applicable on current superconducting devices with nearest-neighbor connections. To rectify the deficiency in connectivity of superconducting circuit system, we experimentally demonstrate a convenient on-chip coupler of centimeters long and propose an extra coupler layer to map the qubit array to a binary-tree connecting graph. This mapping layout reduces the average qubit entangling distance from O(N) to O(logN), demonstrating an exponentially enhanced connectivity with eliminated crosstalk. The entangling gate with the coupler is performed between two fluxonium qubits, reaching a fidelity of 99.37 % while the system static ZZ rate remains as low as 144 Hz without active cancellation or circuit parameter targeting. With the scalable binary tree structure and high-fidelity non-local entanglement, novel quantum algorithms can be implemented on the superconducting qubit system, positioning it as a strong competitor to other physics systems regarding circuit connectivity.
25
Feb
2025
Enhancing Intrinsic Quality Factors Approaching 10 Million in Superconducting Planar Resonators via Spiral Geometry
This study investigates the use of spiral geometry in superconducting resonators to achieve high intrinsic quality factors, crucial for applications in quantum computation and quantum
sensing. We fabricated Archimedean Spiral Resonators (ASRs) using domain-matched epitaxially grown titanium nitride (TiN) on silicon wafers, achieving intrinsic quality factors of Qi=(9.6±1.5)×106 at the single-photon level and Qi=(9.91±0.39)×107 at high power, significantly outperforming traditional coplanar waveguide (CPW) resonators.
We conducted a comprehensive numerical analysis using COMSOL to calculate surface participation ratios (PRs) at critical interfaces: metal-air, metal-substrate, and substrate-air. Our findings reveal that ASRs have lower PRs than CPWs, explaining their superior quality factors and reduced coupling to two-level systems (TLSs).