| 1. |
- Akram, Asif, 1978, et al.
(author)
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AEOLIX Reference Book
- 2019
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Reports (other academic/artistic)abstract
- This is a documentation on the AEOLIX Reference Book (ARB), a website created during the project to collect, highlight and present emerging trends, technologies and practices that are of interest to the problem domain of the project (http://reference.aeolix.eu). The purpose of this document is to present the content of the website.
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| 2. |
- Chen, Liangyu, 1994, et al.
(author)
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Transmon qubit readout fidelity at the threshold for quantum error correction without a quantum-limited amplifier
- 2023
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In: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 9:1
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Journal article (peer-reviewed)abstract
- High-fidelity and rapid readout of a qubit state is key to quantum computing and communication, and it is a prerequisite for quantum error correction. We present a readout scheme for superconducting qubits that combines two microwave techniques: applying a shelving technique to the qubit that reduces the contribution of decay error during readout, and a two-tone excitation of the readout resonator to distinguish among qubit populations in higher energy levels. Using a machine-learning algorithm to post-process the two-tone measurement results further improves the qubit-state assignment fidelity. We perform single-shot frequency-multiplexed qubit readout, with a 140 ns readout time, and demonstrate 99.5% assignment fidelity for two-state readout and 96.9% for three-state readout–without using a quantum-limited amplifier.
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| 3. |
- Fadavi Roudsari, Anita, 1978, et al.
(author)
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Three-wave mixing traveling-wave parametric amplifier with periodic variation of the circuit parameters
- 2023
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:5
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Journal article (peer-reviewed)abstract
- We report on the implementation of a near-quantum-limited, traveling-wave parametric amplifier that uses three-wave mixing (3WM). To favor amplification by 3WM, we use superconducting nonlinear asymmetric inductive element (SNAIL) loops, biased with a dc magnetic flux. In addition, we equip the device with dispersion engineering features to create a stopband at the second harmonic of the pump and suppress the propagation of the higher harmonics that otherwise degrade the amplification. With a chain of 440 SNAILs, the amplifier provides up to 20 dB gain and a 3-dB bandwidth of 1 GHz. The added noise by the amplifier is found to be less than one photon.
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| 4. |
- Grigoras, K., et al.
(author)
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Qubit-Compatible Substrates With Superconducting Through-Silicon Vias
- 2022
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In: IEEE Transactions on Quantum Engineering. - 2689-1808. ; 3
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Journal article (peer-reviewed)abstract
- We fabricate and characterize superconducting through-silicon vias and electrodes suitable for superconducting quantum processors. We measure internal quality factors of a million for test resonators excited at single-photon levels, on chips with superconducting vias used to stitch ground planes on the front and back sides of the chips. This resonator performance is on par with the state of the art for silicon-based planar solutions, despite the presence of vias. Via stitching of ground planes is an important enabling technology for increasing the physical size of quantum processor chips, and is a first step toward more complex quantum devices with three-dimensional integration.
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| 5. |
- Gustafsson, Magnus, 1965, et al.
(author)
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Writing in the disciplines as writing to learn – student disciplinary discourse to enhance learning
- 2017
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In: 9th Conference of the European Association for the Teaching of Academic Writing (EATAW).
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Conference paper (peer-reviewed)abstract
- Irrespective of educational level or language context, we tend to talk of 'writing-to-learn' (WTL) often in general, across discipline ways or we tend to use WTL-techniques in 'pre-writing' stages for the respective student writing projects we are involved in or scaffold. In this presentation, we would like to take a look at WTL from the disciplinary angle (MSc-level engineering) and present results on learning (learning outcomes met via assignments and / or the exams) from two different MSc-level courses at a university of technology. Both the courses have gone through course re-design in connection with faculty training courses. The re-design components vary between the two courses but share the focus of scaffolding student writing for lab reporting writing and involve workshops, peer response, criteria design and negotiation. Technically, the examples can also be addressed as 'writing-in-the-disciplines' of course and the various discipline-specific details that are different in the expected internalized standards of the two disciplines are represented. However, while the writing assignments in the two courses and many techniques in the courses are recognizable as disciplinary writing, our focus is on the design of writing assignments and their effect on disciplinary learning. In this choice of focus on the WTL-dimension, we follow Carter, Ferzli, Wiehe (2007) in an attempt to help show improved student learning also for writing assignments other than pre-writing activities.
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| 6. |
- Kosen, Sandoko, 1991, et al.
(author)
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Building blocks of a flip-chip integrated superconducting quantum processor
- 2022
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In: Quantum Science and Technology. - : IOP Publishing. - 2058-9565. ; 7:3
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Journal article (peer-reviewed)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 mu s, 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.
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| 7. |
- Krantz, Philip, 1984, et al.
(author)
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Investigation of nonlinear effects in Josephson parametric oscillators used in circuit quantum electrodynamics
- 2013
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. (article nr) 105002-
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Journal article (peer-reviewed)abstract
- We experimentally study the behavior of a parametrically pumped nonlinear oscillator, which is based on a superconducting quarter wavelength resonator, and is terminated by a flux-tunable superconducting quantum interference device. We extract parameters for two devices. In particular, we study the effect of the nonlinearities in the system and compare to theory. The Duffing nonlinearity is determined from the probe-power dependent frequency shift of the oscillator, and the nonlinearity related to the parametric flux pumping, is determined from the pump amplitude for the onset of parametric oscillations. Both nonlinearities depend on the parameters of the device and can be tuned in situ by the applied dc flux. We also suggest how to cancel the effect of by adding a small dc flux and a pump tone at twice the pump frequency.
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| 8. |
- Krantz, Philip, 1984, et al.
(author)
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Single-shot read-out of a superconducting qubit using a Josephson parametric oscillator
- 2016
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 7:11417
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Journal article (peer-reviewed)abstract
- We propose and demonstrate a read-out technique for a superconducting qubit by dispersively coupling it with a Josephson parametric oscillator. We employ a tunable quarter wavelength superconducting resonator and modulate its resonant frequency at twice its value with an amplitude surpassing the threshold for parametric instability. We map the qubit states onto two distinct states of classical parametric oscillation: one oscillating state, with 185±15 photons in the resonator, and one with zero oscillation amplitude. This high contrast obviates a following quantum-limited amplifier. We demonstrate proof-of-principle, singleshot read-out performance, and present an error budget indicating that this method can surpass the fidelity threshold required for quantum computing.
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| 9. |
- Osman, Amr, 1993, et al.
(author)
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Mitigation of frequency collisions in superconducting quantum processors
- 2023
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In: Physical Review Research. - 2643-1564. ; 5:4
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Journal article (peer-reviewed)abstract
- The reproducibility of qubit parameters is a challenge for scaling up superconducting quantum processors. Signal cross talk imposes constraints on the frequency separation between neighboring qubits. The frequency uncertainty of transmon qubits arising from the fabrication process is attributed to deviations in the Josephson junction area, tunnel barrier thickness, and the qubit shunt capacitor. We decrease the sensitivity to these variations by fabricating larger Josephson junctions and reduce the wafer-level standard deviation in resistance down to 2%. We characterize 32 identical transmon qubits and demonstrate the reproducibility of the qubit frequencies with a 40 MHz standard deviation (i.e., 1%) with qubit quality factors exceeding 2 million. We perform two-level-system (TLS) spectroscopy and observe no significant increase in the number of TLSs causing qubit relaxation. We further show by simulation that for our parametric-gate architecture, and accounting only for errors caused by the uncertainty of the qubit frequency, we can scale up to 100 qubits with an average of only three collisions between quantum-gate transition frequencies, assuming 2% cross talk and 99.9% target gate fidelity.
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| 10. |
- Osman, Amr, 1993, et al.
(author)
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Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
- 2021
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:6
-
Journal article (peer-reviewed)abstract
- We introduce a simplified fabrication technique for Josephson junctions and demonstrate superconducting Xmon qubits with T1 relaxation times averaging above 50 μs (Q > 1.5 × 1 0 6). Current shadow-evaporation techniques for aluminum-based Josephson junctions require a separate lithography step to deposit a patch that makes a galvanic, superconducting connection between the junction electrodes and the circuit wiring layer. The patch connection eliminates parasitic junctions, which otherwise contribute significantly to dielectric loss. In our patch-integrated cross-type junction technique, we use one lithography step and one vacuum cycle to evaporate both the junction electrodes and the patch. This eliminates a key bottleneck in manufacturing superconducting qubits by reducing the fabrication time and cost. In a study of more than 3600 junctions, we show an average resistance variation of 3.7% on a wafer that contains forty 0.5 × 0.5-cm2 chips, with junction areas ranging between 0.01 and 0.16 μm2. The average on-chip spread in resistance is 2.7%, with 20 chips varying between 1.4% and 2%. For the junction sizes used for transmon qubits, we deduce a wafer-level transition-frequency variation of 1.7%-2.5%. We show that 60%-70% of this variation is attributed to junction-area fluctuations, while the rest is caused by tunnel-junction inhomogeneity. Such high frequency predictability is a requirement for scaling-up the number of qubits in a quantum computer.
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