Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

IEEE Transactions on Applied Superconductivity

Design of Scalable Superconducting Quantum Circuits Using Flip-Chip Assembly

Seong Hyeon Park, Dowon Baek, Insung Park, Seungyong Hahn

Published Feb 10, 2023• 4 citations
Publisher

Abstract

We present design results of scalable superconducting quantum circuits using the flip-chip assembly. In order to achieve the longest relaxation time ($T_{1}$) of a qubit possible, gap between two chips in flip-chip assembly is determined to be 12 μm where low surface dielectric loss from two-level system (TLS) defects can be achieved while maintaining large readout coupling strength between two chips in the flip-chip assembly. Superconducting transmon qubit design is then optimized to have a target anharmonicity of 200 MHz and to have the longer$T_{1}$in consideration of surface energy participation ratios of TLS defects within the compact footprint. To achieve strong coupling strength but low qubit to qubit crosstalk (ZZ) for fast and high fidelity multi-qubit gates, direct coupler and compact multi-path coupler designs for coupling qubits are compared by numerically solving Hamiltonian of the coupled two qubits. Monte-Carlo simulation results on the yield rate of the extended circuits indicate that low manufacturing errors are required.

DOI
10.1109/tasc.2023.3244142

Related papers

Low crosstalk modular flip-chip architecture for coupled superconducting qubits

Soeren Ihssen, Simon Geisert, Gabriel Jaumà +10 more

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.

arXiv:2502.19927•Applied Physics Letters•Mar 1, 2025•3 citations

Superconducting qubits in a flip-chip architecture

Christopher R. Conner, Audrey Bienfait, Hung-Shen Chang +8 more

Flip-chip architectures have recently enabled significant scaling-up of multi-qubit circuits and have been used to assemble hybrid quantum systems that combine different substrates, for example, for quantum acoustics experiments. The standard flip-chip method uses superconducting galvanic connections between two substrates, typically implemented using sophisticated indium wafer-bonding systems, which give highly reliable and temperature-cyclable assemblies, but are expensive, somewhat inflexible in design, and require robust substrates that can sustain the large compressive forces required to cold-weld the indium bonds. A much simpler method is to assemble dies using very low-force contacts and air-dried adhesives, although this does not provide a galvanic contact between the dies. Here, we demonstrate that the latter technique can be used to reliably couple superconducting qubit circuits, in which the qubits are on separate dies, without the need for a galvanic connection. We demonstrate full vector qubit control of each qubit on each of the two dies, with high-fidelity single-shot readout, and further demonstrate entanglement-generating excitation swaps as well as benchmark a controlled-Z entangling gate between the two qubits on the two dies. This exemplifies a simple and inexpensive assembly method for two-plus-one-dimensional quantum circuit integration that supports the use of delicate or unusually shaped substrates.

Applied Physics Letters•Jun 7, 2021•53 citations

A Demonstration of Multifloating Superconducting Qubits on a 3-D Flip-Chip Platform With TLS Loss Mitigation via Apertures

Zhen Luo, Thomas Mayer, Daniela Zahn +8 more

Flip-chip platforms are among the most promising approaches for scaling up superconducting qubits in quantum computing. This work presents the design, modeling, and analysis of floating transmon qubits implemented on a 3-D flip-chip platform. A major focus during qubit design is addressing coherence challenges caused by two-level system (TLS) losses, particularly from surface interfaces. TLS losses at the metal-air (MA) interface are mitigated by introducing apertures beneath the qubit pads. The aperture size is optimized to balance two key factors: minimizing total TLS loss and ensuring sufficient coupling strength between the transmon and resonator. Subsequently, a packaged 3-D chip comprising 24 floating transmons is demonstrated. The transmission spectrum is measured, with all readout resonators successfully located at their designated positions on the spectrum. Two-tone spectroscopy is demonstrated, enabling precise measurement of the qubit frequency.

IEEE Microwave and Wireless Technology Letters•Apr 23, 2025•2 citations

Building blocks of a flip-chip integrated superconducting quantum processor

Sandoko Kosen, Hang-Xi Li, Marcus Rommel +24 more

Abstract We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips—one quantum chip and one control chip—that are bump-bonded together. We demonstrate time-averaged coherence times exceeding 90 μs, single-qubit gate fidelities exceeding 99.9%, and two-qubit gate fidelities above 98.6%. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.

arXiv:2112.02717•Quantum Science and Technology•May 25, 2022•88 citations

Vacuum-gap transmon qubits realized using flip-chip technology

Xuegang Li, Yingshan Zhang, Chuhong Yang +26 more

Significant progress has been made in building large-scale superconducting quantum processors based on flip-chip technology. In this work, we use flip-chip technology to realize a modified transmon qubit, denoted as the “flipmon,” whose large shunt capacitor is replaced by a vacuum-gap parallel plate capacitor. We place one of the qubit pads and a single Josephson junction on the bottom chip and the other pad on the top chip, which is galvanically connected with the junction through an indium bump. The electric field energy participation ratio can arrive at nearly 53% in air when the vacuum-gap is about 5 μm, thus potentially leading to a lower dielectric loss. The coherence times of the flipmons are obtained in the range of 30–60 μs, which are comparable with that of conventional transmons with similar fabrication processes. The electric field simulation indicates that the metal-air interface's energy participation ratio increases significantly and may dominate the flipmon's decoherence. This suggests that more careful surface treatment needs to be considered. No evidence shows that the indium bumps inside the flipmons cause significant decoherence. With well-designed geometry and good surface treatment, the coherence of the flipmons can be further improved.

arXiv:2106.00341•Applied Physics Letters•Nov 1, 2021•32 citations

Tunable-coupling architectures with capacitively connecting pads for large-scale superconducting multiqubit processors

Gui-Han Liang, Xiaohui Song, Cheng-Lin Deng +20 more

We have proposed and experimentally verified a tunable interqubit coupling scheme for large-scale integration of superconducting qubits. The key feature of the scheme is the insertion of connecting pads between the qubit and tunable coupling element. In such a way, the distance between two qubits can be increased considerably to a few millimeters, leaving enough space for arranging control lines, readout resonators, and other necessary structures. The increased interqubit distance provides more wiring space for the flip-chip process and reduces crosstalk between qubits and from control lines to qubits. We use the term tunable coupler with capacitively connecting pad (TCCP) to name the tunable coupling part that consists of a transmon coupler and capacitively connecting pads. With the different placement of connecting pads, different TCCP architectures can be realized. We have designed and fabricated a few multiqubit devices in which TCCP is used for coupling. The measured results show that the performance of the qubits coupled by TCCP, such as ${T}_{1}$ and ${T}_{2}$, was similar to that of traditional transmon qubits without TCCP. Meanwhile, our TCCP also exhibited a wide tunable range of the effective coupling strength and a low residual $ZZ$ interaction between the qubits by properly tuning parameters on the design. Finally, we successfully implemented an adiabatic controlled-$Z$ gate with TCCP. Furthermore, by introducing TCCP, we also discuss the realization of the flip-chip process and tunable coupling qubits between different chips.

arXiv:2306.05312•Physical Review Applied•Oct 10, 2023•16 citations
We present design results of scalable superconducting quantum circuits using the flip-chip assembly. In order to achieve the longest relaxation time (T1T_{1}T1​) of a qubit possible, gap between two chips in flip-chip assembly is determined to be 12 μm where low surface dielectric loss from two-level system (TLS) defects can be achieved while maintaining large readout coupling strength between two chips in the flip-chip assembly. Superconducting transmon qubit design is then optimized to have a target anharmonicity of 200 MHz and to have the longerT1T_{1}T1​in consideration of surface energy participation ratios of TLS defects within the compact footprint. To achieve strong coupling strength but low qubit to qubit crosstalk (ZZ) for fast and high fidelity multi-qubit gates, direct coupler and compact multi-path coupler designs for coupling qubits are compared by numerically solving Hamiltonian of the coupled two qubits. Monte-Carlo simulation results on the yield rate of the extended circuits indicate that low manufacturing errors are required.
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.
Flip-chip architectures have recently enabled significant scaling-up of multi-qubit circuits and have been used to assemble hybrid quantum systems that combine different substrates, for example, for quantum acoustics experiments. The standard flip-chip method uses superconducting galvanic connections between two substrates, typically implemented using sophisticated indium wafer-bonding systems, which give highly reliable and temperature-cyclable assemblies, but are expensive, somewhat inflexible in design, and require robust substrates that can sustain the large compressive forces required to cold-weld the indium bonds. A much simpler method is to assemble dies using very low-force contacts and air-dried adhesives, although this does not provide a galvanic contact between the dies. Here, we demonstrate that the latter technique can be used to reliably couple superconducting qubit circuits, in which the qubits are on separate dies, without the need for a galvanic connection. We demonstrate full vector qubit control of each qubit on each of the two dies, with high-fidelity single-shot readout, and further demonstrate entanglement-generating excitation swaps as well as benchmark a controlled-Z entangling gate between the two qubits on the two dies. This exemplifies a simple and inexpensive assembly method for two-plus-one-dimensional quantum circuit integration that supports the use of delicate or unusually shaped substrates.
Flip-chip platforms are among the most promising approaches for scaling up superconducting qubits in quantum computing. This work presents the design, modeling, and analysis of floating transmon qubits implemented on a 3-D flip-chip platform. A major focus during qubit design is addressing coherence challenges caused by two-level system (TLS) losses, particularly from surface interfaces. TLS losses at the metal-air (MA) interface are mitigated by introducing apertures beneath the qubit pads. The aperture size is optimized to balance two key factors: minimizing total TLS loss and ensuring sufficient coupling strength between the transmon and resonator. Subsequently, a packaged 3-D chip comprising 24 floating transmons is demonstrated. The transmission spectrum is measured, with all readout resonators successfully located at their designated positions on the spectrum. Two-tone spectroscopy is demonstrated, enabling precise measurement of the qubit frequency.
Abstract We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips—one quantum chip and one control chip—that are bump-bonded together. We demonstrate time-averaged coherence times exceeding 90 μs, single-qubit gate fidelities exceeding 99.9%, and two-qubit gate fidelities above 98.6%. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.
Significant progress has been made in building large-scale superconducting quantum processors based on flip-chip technology. In this work, we use flip-chip technology to realize a modified transmon qubit, denoted as the “flipmon,” whose large shunt capacitor is replaced by a vacuum-gap parallel plate capacitor. We place one of the qubit pads and a single Josephson junction on the bottom chip and the other pad on the top chip, which is galvanically connected with the junction through an indium bump. The electric field energy participation ratio can arrive at nearly 53% in air when the vacuum-gap is about 5 μm, thus potentially leading to a lower dielectric loss. The coherence times of the flipmons are obtained in the range of 30–60 μs, which are comparable with that of conventional transmons with similar fabrication processes. The electric field simulation indicates that the metal-air interface's energy participation ratio increases significantly and may dominate the flipmon's decoherence. This suggests that more careful surface treatment needs to be considered. No evidence shows that the indium bumps inside the flipmons cause significant decoherence. With well-designed geometry and good surface treatment, the coherence of the flipmons can be further improved.
We have proposed and experimentally verified a tunable interqubit coupling scheme for large-scale integration of superconducting qubits. The key feature of the scheme is the insertion of connecting pads between the qubit and tunable coupling element. In such a way, the distance between two qubits can be increased considerably to a few millimeters, leaving enough space for arranging control lines, readout resonators, and other necessary structures. The increased interqubit distance provides more wiring space for the flip-chip process and reduces crosstalk between qubits and from control lines to qubits. We use the term tunable coupler with capacitively connecting pad (TCCP) to name the tunable coupling part that consists of a transmon coupler and capacitively connecting pads. With the different placement of connecting pads, different TCCP architectures can be realized. We have designed and fabricated a few multiqubit devices in which TCCP is used for coupling. The measured results show that the performance of the qubits coupled by TCCP, such as T1{T}_{1}T1​ and T2{T}_{2}T2​, was similar to that of traditional transmon qubits without TCCP. Meanwhile, our TCCP also exhibited a wide tunable range of the effective coupling strength and a low residual ZZZZZZ interaction between the qubits by properly tuning parameters on the design. Finally, we successfully implemented an adiabatic controlled-ZZZ gate with TCCP. Furthermore, by introducing TCCP, we also discuss the realization of the flip-chip process and tunable coupling qubits between different chips.