| 1. |
- Greibe, Tine, 1974, et al.
(författare)
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Are "Pinholes" the Cause of Excess Current in Superconducting Tunnel Junctions? A Study of Andreev Current in Highly Resistive Junctions
- 2011
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 106:9
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Tidskriftsartikel (refereegranskat)abstract
- In highly resistive superconducting tunnel junctions, excess subgap current is usually observed and is often attributed to microscopic pinholes in the tunnel barrier. We have studied the subgap current in superconductor-insulator-superconductor (SIS) and superconductor-insulator-normal-metal ( SIN) junctions. In Al/AlOx/Al junctions, we observed a decrease of 2 orders of magnitude in the current upon the transition from the SIS to the SIN regime, where it then matched theory. In Al/AlOx/Cu junctions, we also observed generic features of coherent diffusive Andreev transport in a junction with a homogenous barrier. We use the quasiclassical Keldysh-Green function theory to quantify single- and two-particle tunneling and find good agreement with experiment over 2 orders of magnitude in transparency. We argue that our observations rule out pinholes as the origin of the excess current.
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| 2. |
- Greibe, Tine, 1974, et al.
(författare)
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Improvement of chip design to reduce resonances in subgap regime of Josephson junctions
- 2009
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 150, s. 052063-
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Konferensbidrag (refereegranskat)abstract
- Excess current peaks in the IV curves of SIS Josephson junctions have been observed by some groups [1–3]. These peaks have the shape of a resonance as a function of voltage. The resonances appear in the subgap regime of the junctions and the subgap current (leakage current) is concealed. The positions of the resonances do not change as a magnetic field is applied to the junctions, but their amplitude decreases when the supercurrent is suppressed. We have measured the subgap current of Al/AlOx/Al junctions and we show that these resonances are due to resonant modes in the chip design which are excited by the ac-Josephson effect. We present a chip design that decreases the amplitude of the resonances to a such degree that the subgap current is quantifiable.
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| 3. |
- Sandberg, Martin, 1977, et al.
(författare)
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Fast tuning of superconducting microwave cavities
- 2008
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Ingår i: Proc. 2nd International Workshop on Solid-State Quantum Computing. - 9780735406056 ; , s. 12-21
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Konferensbidrag (refereegranskat)abstract
- Photons are fundamental excitations of electromagnetic fields and can be captured in cavities. For a given cavity with a certain size, the fundamental mode has a fixed frequency f which gives the photons a specific "color". The cavity also has a typical lifetime tau, which results in a finite linewidth delta f. If the size of the cavity is changed fast compared to tau, and so that the frequency change Delta f >> delta f, then it is possible to change the "color" of the captured photons. Here we demonstrate superconducting microwave cavities, with tunable effective lengths. The tuning is obtained by varying a Josephson inductance at one end of the cavity. We show data on four different samples and demonstrate tuning by several hundred linewidths in a time Delta t
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| 4. |
- Sandberg, Martin, 1977, et al.
(författare)
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Tuning the field in a microwave resonator faster than the photon lifetime
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:20, s. 203501-
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated and characterized tunable superconducting transmission line resonators. To change the resonance frequency, we modify the boundary condition at one end of the resonator through the tunable Josephson inductance of a superconducting quantum interference device. We demonstrate a large tuning range (several hundred megahertz), high quality factors (10(4)), and that we can change the frequency of a few-photon field on a time scale orders of magnitude faster than the photon lifetime of the resonator. This demonstration has implications in a variety of applications.
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