| 1. |
- Mannila, E. T., et al.
(författare)
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A superconductor free of quasiparticles for seconds
- 2021
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481.
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting devices, based on the Cooper pairing of electrons, play an important role in existing and emergent technologies, ranging from radiation detectors1,2 to quantum computers3. Their performance is limited by spurious quasiparticle excitations formed from broken Cooper pairs4–12. Efforts to achieve ultra-low quasiparticle densities have reached time-averaged numbers of excitations on the order of one in state-of-the-art devices2,12–15. However, the dynamics of the quasiparticle population as well as the timescales for adding and removing individual excitations remain largely unexplored. Here, we experimentally demonstrate a superconductor completely free of quasiparticles for periods lasting up to seconds. We monitor the quasiparticle number on a mesoscopic superconductor in real time by measuring the charge tunnelling to a normal metal contact. Quiet, excitation-free periods are interrupted by random-in-time Cooper pair breaking events, followed by a burst of charge tunnelling within a millisecond. Our results demonstrate the possibility of operating devices without quasiparticles with potentially improved performance. In addition, our experiment probes the origins of nonequilibrium quasiparticles in our device. The decay of the Cooper pair breaking rate over several weeks following the initial cooldown rules out processes arising from cosmic or long-lived radioactive sources16–19.
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| 2. |
- Nguyen, H. Q., et al.
(författare)
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Electrostatic control of quasiparticle poisoning in a hybrid semiconductor-superconductor island
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 108:4
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Tidskriftsartikel (refereegranskat)abstract
- The performance of superconducting devices is often degraded by the uncontrolled appearance and disappearance of quasiparticles, a process known as poisoning. We demonstrate the electrostatic control of quasiparticle poisoning in the form of single-charge tunneling across a fixed barrier onto a Coulomb island in an InAs/Al hybrid nanowire. High-bandwidth charge sensing was used to monitor the charge occupancy of the island across Coulomb blockade peaks, where tunneling rates were maximal, and Coulomb valleys, where tunneling was absent. Electrostatic gates changed the on-peak tunneling rates by two orders of magnitude for a barrier with fixed normal-state resistance, which we attribute to the gate dependence of the size and softness of the induced superconducting gap on the island, corroborated by separate density-of-states measurements. Temperature and magnetic field dependence of tunneling rates are also investigated.
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| 3. |
- Gasparinetti, S., et al.
(författare)
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Fast Electron Thermometry for Ultrasensitive Calorimetric Detection
- 2015
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Ingår i: Physical Review Applied. - 2331-7019. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate radio-frequency thermometry on a micrometer-sized metallic island below 100 mK. Our device is based on a normal-metal-insulator-superconductor tunnel junction coupled to a resonator with transmission readout. In the first generation of the device, we achieve 90 mu K/root Hz noise-equivalent temperature with 10 MHz bandwidth. We measure the thermal relaxation time of the electron gas in the island, which we find to be of the order of 100 mu s. Such a calorimetric detector, upon optimization, can be seamlessly integrated into superconducting circuits, with immediate applications in quantum-thermodynamics experiments down to single quanta of energy.
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| 4. |
- Mannila, E. T., et al.
(författare)
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Detecting parity effect in a superconducting device in the presence of parity switches
- 2019
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Ingår i: Physical Review B. - 2469-9950. ; 100:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a superconducting device showing a clear parity effect in the number of electrons, even when there is, on average, a single nonequilibrium quasiparticle present and the parity of the island switches due to quasiparticles tunneling in and out of the device at rates on the order of 100 Hz. We detect the switching by monitoring in real time the charge state of a superconducting island connected to normal leads by tunnel junctions. The quasiparticles are created by Cooper pairs breaking on the island at a rate of a few kilohertz. We demonstrate that the pair breaking is caused by the backaction of the single-electron transistor used as a charge detector. With sufficiently low probing currents, our superconducting island is free of quasiparticles 97% of the time.
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| 5. |
- Mannila, E. T., et al.
(författare)
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Self-Calibrating Superconducting Pair-Breaking Detector
- 2021
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Ingår i: Physical Review Letters. - 1079-7114. ; 127:14
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Tidskriftsartikel (refereegranskat)abstract
- We propose and experimentally demonstrate a self-calibrating detector of Cooper pair depairing in a superconductor based on a mesoscopic superconducting island coupled to normal metal leads. On average, exactly one electron passes through the device per broken Cooper pair, independent of the absorber volume, device, or material parameters. The device operation is explained by a simple analytical model and verified with numerical simulations in quantitative agreement with experiment. In a proof-of-concept experiment, we use such a detector to measure the high-frequency phonons generated by another, electrically decoupled superconducting island, with a measurable signal resulting from less than 10 fW of dissipated power.
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