Browsing by Author "Lilja, Ilari"

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  • Design and operation of a broadband Josephson parametric amplifier based on lumped elements
    (2018-10-18) Lilja, Ilari
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Generation and Structuring of Multipartite Entanglement in a Josephson Parametric System
    (2023-01) Petrovnin, Kirill Viktorovich; Perelshtein, Michael Romanovich; Korkalainen, Tero; Vesterinen, Visa; Lilja, Ilari; Paraoanu, Gheorghe Sorin; Hakonen, Pertti Juhani
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Quantum correlations are a vital resource in advanced information processing based on quantum phenomena. Remarkably, the vacuum state of a quantum field may act as a key element for the generation of multipartite quantum entanglement. In this work, generation of genuine tripartite entangled state and its control is achieved by the use of the phase difference between two continuous pump tones. Control of the subspaces of the covariance matrix for tripartite bisqueezed state is demonstrated. Furthermore, by optimizing the phase relationships in a three-tone pumping scheme genuine quadripartite entanglement of a generalized H-graph state (H-graph) is explored. This scheme provides a comprehensive control toolbox for the entanglement structure and allows to demonstrate, for first time to the authors' knowledge, genuine quadripartite entanglement of microwave modes. All experimental results are verified with numerical simulations of the nonlinear quantum Langevin equation. It is envisioned that quantum resources facilitated by multi-pump configurations offer enhanced prospects for quantum data processing using parametric microwave cavities.
  • Generation of multimode entanglement with a Josephson Parametric Oscillator
    (2021-12-14) Lilja, Ilari
     Perustieteiden korkeakoulu | Master's thesis
    Quantum information theory studies how quantum mechanics can be used to solve information processing tasks. The explotation of quantum mechanical properties can lead to quantum information protocols being more efficient than their classical counterparts. Continuous-Variable states offer an attractive platform for implementing various quantum information continuous variable protocols. In this thesis we show how Josephson Parametric Oscillators (JPO) can be used to generate multipartite entangled CV states for the use as a quantum resource in quantum information protocols. By simultaneously driving the JPO with two different pump tones, a tripartite entangled state is generated. The entanglement properties of the tripartite state are entirely contained in its 6-by-6 covariance matrix. Various entanglement measures are applied to the covariance matrix to demonstrate that the generated state exhibits genuine tripartite entanglement.
  • Kinetic inductance in superconducting CoSi2 coplanar microwave transmission lines
    (2024-04-01) Mukhanova, Ekaterina; Zeng, Weijun; Heredia, Elica Anne; Wu, Chun Wei; Lilja, Ilari; Lin, Juhn Jong; Yeh, Sheng Shiuan; Hakonen, Pertti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We have looked into cobalt disilicide (CoSi2) as a potential building block for superconducting quantum circuits. In order to achieve this, we annealed a thin layer of Co to create microwave cavities with thickness of d = 10-105 nm from CoSi2 embedded in the silicon substrate. The cavity properties were measured as a function of temperature and power. In the films measuring 10 and 25 nm, we find a significant kinetic inductance LK with a non-BCS power-law variation δLK ∝ T4.3±0.2 at low temperatures. The quality factor of the studied microwave resonances varied from 3 × 103 (d = 10 nm) to ∼5 × 104 (d = 105 nm) and increased as d(A − log d) with thickness, with two-level systems having very little effect. The power dependence of kinetic inductance was analyzed in terms of heat flow due to electron-phonon coupling, which was found to be stronger than estimated for heat relaxation by regular quasiparticles.
  • Switching dynamics in Al/InAs nanowire-based gate-controlled superconducting switch
    (2024-12) Elalaily, Tosson; Berke, Martin; Lilja, Ilari; Savin, Alexander; Fülöp, Gergő; Kupás, Lőrinc; Kanne, Thomas; Nygård, Jesper; Makk, Péter; Hakonen, Pertti; Csonka, Szabolcs
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The observation of the gate-controlled supercurrent (GCS) effect in superconducting nanostructures increased the hopes for realizing a superconducting equivalent of semiconductor field-effect transistors. However, recent works attribute this effect to various leakage-based scenarios, giving rise to a debate on its origin. A proper understanding of the microscopic process underlying the GCS effect and the relevant time scales would be beneficial to evaluate the possible applications. In this work, we observed gate-induced two-level fluctuations between the superconducting state and normal state in Al/InAs nanowires (NWs). Noise correlation measurements show a strong correlation with leakage current fluctuations. The time-domain measurements show that these fluctuations have Poissonian statistics. Our detailed analysis of the leakage current measurements reveals that it is consistent with the stress-induced leakage current (SILC), in which inelastic tunneling with phonon generation is the predominant transport mechanism. Our findings shed light on the microscopic origin of the GCS effect and give deeper insight into the switching dynamics of the superconducting NW under the influence of the strong gate voltage.