@article{22619, abstract = {Planar germanium is currently the only semiconducting platform where high-coherence spin qubits and proximity-induced superconductivity have each been demonstrated. Recent research into spin qubits in Ge/SiGe heterostructures has focused on increasing the thickness of the SiGe capping layer, reporting improvements in the electrostatic noise levels. Meanwhile, heterostructures with thinner capping layers remain rather unexplored, despite the potential advantages for proximity-induced superconductivity. Here, we study a Ge/SiGe heterostructure with a thin SiGe cap d - 4nm and investigate its viability to host low-noise quantum dots. To keep the thermal budget compatible with superconducting layers, low-temperature oxide deposition processes were developed and implemented for the gate dielectrics. The charge noise level of the fabricated devices is estimated to be 1.8  +- 1.0 μeV/ square HZ⁠, comparable to devices fabricated on shallow heterostructures (⁠ d - 20nm⁠) with high-temperature deposited oxides. Low charge noise levels, together with the straightforward integration of superconductors, make this heterostructure an attractive platform for prototyping hybrid semiconducting–superconducting devices.}, author = {Borovkov, Maksim and Schell, Yona A and Sokolova, Dina and Roux, Kevin Etienne Robert and Falthansl-Scheinecker, Paul and Fabris, Giorgio and Shah, Devashish C and Saez Mollejo, Jaime and Previdi, Rodolfo and Taha, Inas and Genç, Aziz and Arbiol, Jordi and Calcaterra, Stefano and Oliveira, Afonso De Cerdeira and Chrastina, Daniel and Isella, Giovanni and Bubis, Anton and Katsaros, Georgios}, issn = {1077-3118}, journal = {Applied Physics Letters}, number = {3}, publisher = {AIP Publishing}, title = {{Low-noise quantum dots in ultra-shallow Ge/SiGe heterostructures for prototyping hybrid semiconducting–superconducting devices}}, doi = {10.1063/5.0333142}, volume = {129}, year = {2026}, } @article{20976, abstract = {We present an experimental demonstration of an impedance-engineered Josephson parametric amplifier (IEJPA) fabricated in a single-step lithography process. Impedance-engineering is implemented using a lumped-element series LC circuit. We use a simpler lithography process where the entire device—impedance transformer and Josephson parametric amplifier (JPA)—is patterned in a single electron beam lithography step, followed by a double-angle Dolan-bridge technique for Al–AlOx–Al deposition. We observe amplification with 18 dB gain over a wide 400 MHz bandwidth centered around 5.3 GHz with added noise approaching the quantum limit, and a saturation power of −114 dBm. To accurately explain our experimental results, we extend existing theories for IEJPAs to incorporate the full sine nonlinearity of both the JPA and the transformer. Our work provides a route to simpler realization of broadband JPAs and a theoretical foundation for a regime of JPA operation that has been less explored in literature.}, author = {Patel, Lipi and Hawaldar, Samarth and Panikkar, Aditya and Shankar, Athreya and Suri, Baladitya}, issn = {1077-3118}, journal = {Applied Physics Letters}, number = {25}, publisher = {AIP Publishing}, title = {{Impedance-engineered Josephson parametric amplifier with single-step lithography}}, doi = {10.1063/5.0290636}, volume = {127}, year = {2025}, } @article{21552, abstract = {We present full-Maxwell topology-optimization design of a single-piece multilayer metalens, about 10 wavelengths λ in thickness, which simultaneously focuses over a 60° angular range and a 23% spectral bandwidth without suffering chromatic or angular aberration, a “plan-achromat.” At all angles and frequencies, it achieves diffraction-limited focusing (Strehl ratio >0.8) and an absolute focusing efficiency of >50%. Both 2D and 3D axisymmetric designs are presented, optimized over ∼105 degrees of freedom. We also demonstrate shortening the lens-to-sensor distance while producing the same image as for a longer “virtual” focal length and maintaining plan-achromaticity. These proof-of-concept designs demonstrate the ultra-compact multifunctionality that can be achieved by exploiting the full wave physics of subwavelength designs and motivate future work on design and fabrication of multilayer metaoptics.}, author = {Lin, Zin and Roques-Carmes, Charles and Christiansen, Rasmus E. and Soljačić, Marin and Johnson, Steven G.}, issn = {1077-3118}, journal = {Applied Physics Letters}, number = {4}, publisher = {AIP Publishing}, title = {{Computational inverse design for ultra-compact single-piece metalenses free of chromatic and angular aberration}}, doi = {10.1063/5.0035419}, volume = {118}, year = {2021}, } @article{8746, abstract = {Research in the field of colloidal semiconductor nanocrystals (NCs) has progressed tremendously, mostly because of their exceptional optoelectronic properties. Core@shell NCs, in which one or more inorganic layers overcoat individual NCs, recently received significant attention due to their remarkable optical characteristics. Reduced Auger recombination, suppressed blinking, and enhanced carrier multiplication are among the merits of core@shell NCs. Despite their importance in device development, the influence of the shell and the surface modification of the core@shell NC assemblies on the charge carrier transport remains a pertinent research objective. Type-II PbTe@PbS core@shell NCs, in which exclusive electron transport was demonstrated, still exhibit instability of their electron ransport. Here, we demonstrate the enhancement of electron transport and stability in PbTe@PbS core@shell NC assemblies using iodide as a surface passivating ligand. The combination of the PbS shelling and the use of the iodide ligand contributes to the addition of one mobile electron for each core@shell NC. Furthermore, both electron mobility and on/off current modulation ratio values of the core@shell NC field-effect transistor are steady with the usage of iodide. Excellent stability in these exclusively electron-transporting core@shell NCs paves the way for their utilization in electronic devices. }, author = {Miranti, Retno and Septianto, Ricky Dwi and Ibáñez, Maria and Kovalenko, Maksym V. and Matsushita, Nobuhiro and Iwasa, Yoshihiro and Bisri, Satria Zulkarnaen}, issn = {1077-3118}, journal = {Applied Physics Letters}, number = {17}, publisher = {AIP Publishing}, title = {{Electron transport in iodide-capped core@shell PbTe@PbS colloidal nanocrystal solids}}, doi = {10.1063/5.0025965}, volume = {117}, year = {2020}, } @article{1743, abstract = {Laterally aligned multilayer GeSiSi islands grown on a patterned Si (001) substrate are disclosed by selective etching of Si in a KOH solution. This procedure allows us to visualize the vertical alignment of the islands in a three-dimensional perspective. Our technique reveals that partly coalesced double islands in the initial layer do not merge together, but instead gradually reproduce into well-separated double islands in upper layers. We attribute this effect to very thin spacer layers, which efficiently transfer the strain modulation of each island through the spacer layer to the surface. The etching rate of Si is reduced in tensile strained regions, which helps to preserve sufficient Si between the stacked islands to form a periodic array of freestanding and vertically modulated heterostructure pillars.}, author = {Zhong, Zheyang and Katsaros, Georgios and Stoffel, Mathieu and Costantini, Giovanni and Kern, Klaus and Schmidt, Oliver and Jin Phillipp, Neng and Bauer, Günther}, issn = {1077-3118}, journal = {Applied Physics Letters}, number = {26}, pages = {1 -- 3}, publisher = {American Institute of Physics}, title = {{Periodic pillar structures by Si etching of multilayer GeSi/Si islands}}, doi = {10.1063/1.2150278}, volume = {87}, year = {2005}, }