| 1. |
- Frigerio, Jacopo, et al.
(författare)
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Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics
- 2021
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:12, s. 3573-3582
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Tidskriftsartikel (refereegranskat)abstract
- Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, the silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, Ge-rich epilayers allow for waveguiding on a Si substrate. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 μm. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility χ(2) almost reaches 105 pm/V, 4 orders of magnitude larger than bulk nonlinear materials for which, by the Miller's rule, the range of 10 pm/V is the norm.
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| 2. |
- Frigerio, Jacopo, et al.
(författare)
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Mid-infrared second harmonic generation in Ge/SiGe coupled quantum wells
- 2020
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Ingår i: 2020 IEEE Photonics Conference, IPC 2020 - Proceedings. ; September 2020
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Konferensbidrag (refereegranskat)abstract
- We present the theoretical investigation and the experimental demonstration of second harmonic generation in the mid-infrared by hole-doped Ge/SiGe asymmetric quantum wells.
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| 3. |
- Frigerio, Jacopo, et al.
(författare)
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Mid-infrared second harmonic generation with Ge quantum wells
- 2021
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Ingår i: IEEE International Conference on Group IV Photonics GFP. - 1949-2081. ; 2021-December
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Konferensbidrag (refereegranskat)abstract
- We present the experimental demonstration of second harmonic generation in the mid-infrared by hole-doped Ge/SiGe asymmetric quantum wells.
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| 4. |
- Valentini, Marco, et al.
(författare)
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Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium
- 2024
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Ingår i: Nature Communications. - 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a sin(2 φ) CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with ≈ 100% efficiency. The reported results open up the path towards integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on the same silicon technology compatible platform.
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