| 1. |
- Scigliuzzo, Marco, 1987, et al.
(författare)
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Phononic loss in superconducting resonators on piezoelectric substrates
- 2020
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 22:5
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Tidskriftsartikel (refereegranskat)abstract
- We numerically and experimentally investigate the phononic loss for superconducting resonators fabricated on a piezoelectric substrate. With the help of finite element method simulations, we calculate the energy loss due to electromechanical conversion into bulk and surface acoustic waves. This sets an upper limit for the resonator internal quality factor Q i. To validate the simulation, we fabricate quarter wavelength coplanar waveguide resonators on GaAs and measure Q i as function of frequency, power and temperature. We observe a linear increase of Q i with frequency, as predicted by the simulations for a constant electromechanical coupling. Additionally, Q i shows a weak power dependence and a negligible temperature dependence around 10 mK, excluding two level systems and non-equilibrium quasiparticles as the main source of losses at that temperature.
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| 2. |
- Burnett, Jonathan, 1987, et al.
(författare)
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Decoherence benchmarking of superconducting qubits
- 2019
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- We benchmark the decoherence of superconducting transmon qubits to examine the temporal stability of energy relaxation, dephasing, and qubit transition frequency. By collecting statistics during measurements spanning multiple days, we find the mean parameters (T) over bar (1) = 49 mu s and (T) over bar (2)* = 95 mu s; however, both of these quantities fluctuate, explaining the need for frequent re-calibration in qubit setups. Our main finding is that fluctuations in qubit relaxation are local to the qubit and are caused by instabilities of near-resonant two-level-systems (TLS). Through statistical analysis, we determine sub-millihertz switching rates of these TLS and observe the coherent coupling between an individual TLS and a transmon qubit. Finally, we find evidence that the qubit's frequency stability produces a 0.8 ms limit on the pure dephasing which we also observe. These findings raise the need for performing qubit metrology to examine the reproducibility of qubit parameters, where these fluctuations could affect qubit gate fidelity.
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| 3. |
- Lu, Yong, 1989, et al.
(författare)
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Characterizing decoherence rates of a superconducting qubit by direct microwave scattering
- 2021
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally investigate a superconducting qubit coupled to the end of an open transmission line, in a regime where the qubit decay rates to the transmission line and to its own environment are comparable. We perform measurements of coherent and incoherent scattering, on- and off-resonant fluorescence, and time-resolved dynamics to determine the decay and decoherence rates of the qubit. In particular, these measurements let us discriminate between non-radiative decay and pure dephasing. We combine and contrast results across all methods and find consistent values for the extracted rates. The results show that the pure dephasing rate is one order of magnitude smaller than the non-radiative decay rate for our qubit. Our results indicate a pathway to benchmark decoherence rates of superconducting qubits in a resonator-free setting.
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| 4. |
- Lu, Yong, 1989, et al.
(författare)
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Quantum efficiency, purity and stability of a tunable, narrowband microwave single-photon source
- 2021
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Ingår i: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.
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| 5. |
- Burnett, Jonathan, 1987, et al.
(författare)
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Noise and loss of superconducting aluminium resonators at single photon energies
- 2018
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 969:1
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Konferensbidrag (refereegranskat)abstract
- The loss and noise mechanisms of superconducting resonators are useful tools for understanding decoherence in superconducting circuits. While the loss mechanisms have been heavily studied, noise in superconducting resonators has only recently been investigated. In particular, there is an absence of literature on noise in the single photon limit. Here, we measure the loss and noise of an aluminium on silicon quarter-wavelength (λ/4) resonator in the single photon regime.
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| 6. |
- de Graaf, Sebastian Erik, 1986, et al.
(författare)
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Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evid ence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.
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| 7. |
- Kennedy, O. W., et al.
(författare)
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Tunable Nb Superconducting Resonator Based on a Constriction Nano-SQUID Fabricated with a Ne Focused Ion Beam
- 2019
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Ingår i: Physical Review Applied. - 2331-7019. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid superconducting-spin systems offer the potential to combine highly coherent atomic quantum systems with the scalability of superconducting circuits. To fully exploit this potential requires a high-quality-factor microwave resonator, tunable in frequency and able to operate at magnetic fields optimal for the spin system. Such magnetic fields typically rule out conventional Al-based Josephson-junction devices that have previously been used for tunable high-Q microwave resonators. The larger critical field of Nb allows microwave resonators with large field resilience to be fabricated. Here we demonstrate how constriction-type weak links, patterned in parallel into the central conductor of a Nb coplanar resonator with a neon focused ion beam, can be used to implement a frequency-tunable resonator. We study transmission through two such devices and show how they realize high-quality-factor, tunable, field-resilient devices that hold promise for future applications coupling to spin systems.
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| 8. |
- Niepce, David, 1984, et al.
(författare)
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Geometric scaling of two-level-system loss in superconducting resonators
- 2020
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 33:2
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Tidskriftsartikel (refereegranskat)abstract
- We perform an experimental and numerical study of dielectric loss in superconducting microwave resonators at low temperature. Dielectric loss, due to two-level systems, is a limiting factor in several applications, e.g. superconducting qubits, Josephson parametric amplifiers, microwave kinetic-inductance detectors, and superconducting single-photon detectors. Our devices are made of disordered NbN, which, due to magnetic-field penetration, necessitates 3D finite-element simulation of the Maxwell-London equations at microwave frequencies to accurately model the current density and electric field distribution. From the field distribution, we compute the geometric filling factors of the lossy regions in our resonator structures and fit the experimental data to determine the intrinsic loss tangents of its interfaces and dielectrics. We put emphasis on the loss caused by a spin-on-glass resist such as hydrogen silsesquioxane (HSQ), used for ultrahigh lithographic resolution relevant to the fabrication of nanowires. We find that, when used, HSQ is the dominant source of loss, with a loss tangent ofδHSQi=× 10-3 SRC.
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| 9. |
- Niepce, David, 1984, et al.
(författare)
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High Kinetic Inductance Nb N Nanowire Superinductors
- 2019
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Ingår i: Physical Review Applied. - 2331-7019. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that a high kinetic inductance disordered-superconductor nanowire can realize a circuit element - known as a superinductor - with a characteristic impedance greater than the quantum resistance (RQ=h/4e2≃6.5kΩ) and a quality factor of 25 000 at single-photon excitation. By examining loss rates, we demonstrate that the microwave dissipation can be fully understood in the framework of two-level-system dielectric loss. Superinductors can suppress the quantum fluctuations of charge in a circuit, which has applications, for example, in devices for quantum computing, photon detection, and other sensors based on mesoscopic circuits.
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