Narrow long Josephson junctions

Koval, Y.; Wallraff, Andreas; Fistul, M. V.; Thyssen, N.; Kohlstedt, H.; Ustinov, A. V.

doi:10.1109/77.783894

Cited by 17 publications

(28 citation statements)

References 11 publications

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“…1(a) and 1(b)). For experiments, we fabricated a junction of diameter d 100 m and width w 0:5 m which was etched from a sputtered Nb=AlO x =Nb thin film trilayer and patterned using electron-beam lithography [18]. Its critical current density is 220 A=cm 2 , the Josephson length is J 30 m, and the normalized junction length is L d= J 10:5.…”

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confidence: 99%

Quantum Dissociation of a Vortex-Antivortex Pair in a Long Josephson Junction

Fistul

Wallraff²,

Koval³

et al. 2003

Phys. Rev. Lett.

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The thermal and the quantum dissociation of a single vortex-antivortex (VAV) pair in an annular Josephson junction is experimentally observed and theoretically analyzed. In our experiments, the VAV pair is confined in a pinning potential controlled by external magnetic field and bias current. The dissociation of the pinned VAV pair manifests itself in a switching of the Josephson junction from the superconducting to the resistive state. The observed temperature and field dependence of the switching current distribution is in agreement with the analysis. The crossover from the thermal to the macroscopic quantum tunneling mechanism of dissociation occurs at a temperature of about 100 mK. We also predict the specific magnetic field dependence of the oscillatory energy levels of the pinned VAV state.

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confidence: 99%

Quantum Dissociation of a Vortex-Antivortex Pair in a Long Josephson Junction

Fistul

Wallraff²,

Koval³

et al. 2003

Phys. Rev. Lett.

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“…The junction area was defined in a sputtered Nb/AlO x /Nb trilayer by using electron-beam lithography and reactive ion etching. For insulation of the trilayer edges we used highly cross-linked PMMA [15]. The critical current density of the trilayer is about 220 A/cm 2 .…”

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confidence: 99%

Enhancement of Josephson Phase Diffusion by Microwaves

2004

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We report an experimental and theoretical study of the phase diffusion in small Josephson junctions under microwave irradiation. A peculiar enhancement of the phase diffusion by microwaves is observed. The enhancement manifests itself by a pronounced current peak in the current-voltage characteristics. The voltage position Vtop of the peak increases with the power P of microwave radiation as Vtop ∝ √ P , while its current amplitude weakly decreases with P . As the microwave frequency increases, the peak feature evolves into Shapiro steps with finite slope. Our theoretical analysis taking into account the enhancement of incoherent superconducting current by multi-photon absorption is in good agreement with experimental data. [5,6], to name just a few. The significance of these various effects depends on the ratio of the Josephson energy E J to the charging energy E C and on the thermal fluctuations. Here, we will deal with properties of moderately small Josephson tunnel junctions, with the ratio of E J /E C ≫ 1, and E J ≃ k B T , which corresponds to the phase diffusion regime induced by thermal fluctuations.The Josephson phase diffusion in small junctions has been studied in detail both experimentally [5,7] and theoretically [8,9]. Recently, the phase diffusion regime has been observed also in layered high-temperature superconductors [10]. The characteristic feature of this regime is the absence of pure zero-voltage superconducting state accompanied, however, by a hysteresis in the I-V curve. The phase diffusion behavior is a consequence of frequency dependent damping [5], i.e. the dissipation can be rather weak at zero frequency but it reaches a substan- * Present address: Theoretische Physik III, Ruhr

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“…1.1c. The junction of diameter d = 100 µm and width w = 0.5 µm is etched from a sputtered Nb/AlO x /Nb thin film trilayer which is patterned using electron-beam lithography [29]. A photograph of the sample taken using an optical microscope is shown in Fig.…”

Section: Quantum Tunnellingmentioning

confidence: 99%

“…1.4a-b). For experiments we fabricated a junction of diameter d = 100 µm and width w = 0.5 µm which was etched from a sputtered Nb/AlO x /Nb thin film trilayer and patterned using electron-beam lithography [29]. Its critical current density is 220 A/cm 2 , the Josephson length is λ J ≈ 30 µm and the normalized junction length is L ≡ πd/λ J ≈ 10.5.…”

Section: Thermal and Quantum Dissociationmentioning

confidence: 99%

Quantum Dynamics of Vortices and Vortex Qubits

Wallraff

Kemp

Ustinov

2005

Quantum Information Processing

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IntroductionVortices appear naturally in a wide range of gases and fluids, both on very large scales, e.g. when tornados form in the earths atmosphere, and on very small scales, e.g. in BoseEinstein condensates of dilute atomic gases [1] or in superfluid helium [2], where their existence is a consequence of the quantum nature of the liquid. Collective nonlinear excitations such as the vortex considered here are ubiquitous in solid state systems (e.g. domain walls), biological systems (e.g. waves on membranes) and have even been considered as model systems in particle physics. In superconductors, which we consider here, quantized vortices of the supercurrent [3], that are generated by magnetic flux penetrating into the material, play a key role in understanding the material properties [4] and the performance of superconductor-based devices [5,6]. At high temperatures the dynamics of vortices is essentially classical. At low temperatures, however, there are experiments suggesting the collective quantum dynamics of vortices [7,8]. Here we report on experiments in which we have probed for the first time the quantum dynamics of an individual vortex in a superconductor. By measuring the statistics of the vortex escape from a controllable pinning potential we were able demonstrate the quantization of the vortex energy within the trapping potential well and the quantum tunnelling of the vortex through the pinning barrier.The object that we have studied in our experiments is a vortex of electric current with a spatial extent of several tens of micrometers formed in a long superconducting tunnel junction. The electrodynamics of such a Josephson junction is governed by the phase difference ϕ between the macroscopic wave functions describing the superconducting condensate in the two electrodes [9]. It is a well established fact that the variable ϕ displays macroscopic quantum properties in point-like junctions at very low temperatures [10,11]. Such macroscopic quantum phenomena are currently exploited for quantum information processing [12] using superconducting devices [10,13,14,15,16,17,18,19,20]. In extended one-or twodimensional Josephson junction systems quantum tunnelling in real space is to be expected for superconducting vortices, which are particle-like collective excitations of the phase difference ϕ. The small value of the expected mass of the vortex studied here suggests that quantum effects are likely to occur with vortices at low temperatures. Dissipative vortex tunnelling

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Narrow long Josephson junctions

Cited by 17 publications

References 11 publications

Quantum Dissociation of a Vortex-Antivortex Pair in a Long Josephson Junction

Quantum Dissociation of a Vortex-Antivortex Pair in a Long Josephson Junction

Enhancement of Josephson Phase Diffusion by Microwaves

Quantum Dynamics of Vortices and Vortex Qubits

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