Multi-module microwave assembly for fast read-out and charge noise characterization of silicon quantum dots

Fast measurements of quantum devices is important in areas such as quantum sensing, quantum computing and nanodevice quality analysis. Here, we develop a superconductor-semiconductor multi-module microwave assembly to demonstrate charge state readout at the state-of-the-art. The assembly consist of a superconducting readout resonator interfaced to a silicon-on-insulator (SOI) chiplet containing quantum dots (QDs) in a high-$\kappa$ nanowire transistor. The superconducting chiplet contains resonant and coupling elements as well as $LC$ filters that, when interfaced with the silicon chip, result in a resonant frequency $f=2.12$~GHz, a loaded quality factor $Q=680$, and a resonator impedance $Z=470$~$\Omega$. Combined with the large gate lever arms of SOI technology, we achieve a minimum integration time for single and double QD transitions of 2.77~ns and 13.5~ns, respectively. We utilize the assembly to measure charge noise over 9 decades of frequency up to 500~kHz and find a 1/$f$ dependence across the whole frequency spectrum as well as a charge noise level of 4~$\mu$eV/$\sqrt{\text{Hz}}$ at 1~Hz. The modular microwave circuitry presented here can be directly utilized in conjunction with other quantum device to improve the readout performance as well as enable large bandwidth noise spectroscopy, all without the complexity of superconductor-semiconductor monolithic fabrication.Comment: Main: 7 pages, 4 figures. Supplementary: 6 pages, 5 figure

Large dispersive interaction between a CMOS double quantum dot and microwave photons

We report a large coupling rate, $g_0/(2\pi)=183$ MHz, between the charge state of a double quantum dot in a CMOS split-gate silicon nanowire transistor and microwave photons in a lumped-element resonator formed by hybrid integration with a superconducting inductor. We enhance the coupling by exploiting the large interdot lever arm of an asymmetric split-gate device, $\alpha=0.72$, and by inductively coupling to the resonator to increase its impedance, $Z_\text{r}=560$ $\Omega$. In the dispersive regime, the large coupling strength at the DQD hybridisation point produces a frequency shift comparable to the resonator linewidth, the optimal setting for maximum state visibility. We exploit this regime to demonstrate rapid gate-based readout of the charge degree of freedom, with an SNR of 3.3 in 50 ns. In the resonant regime, the fast charge decoherence rate precludes reaching the strong coupling regime, but we show a clear route to spin-photon circuit quantum electrodynamics using hybrid CMOS systems.Comment: 9 pages, 7 figure

Superconductor-ferromagnet nanocomposites created by co-deposition of niobium and dysprosium

We have created superconductor-ferromagnet composite films in order to test the enhancement of critical current density, Jc, due to magnetic pinning. We co-sputter the type-II superconductor niobium (Nb) and the low-temperature ferromagnet dysprosium (Dy) onto a heated substrate; the immiscibility of the two materials leads to a phase-separated composite of magnetic regions within a superconducting matrix. Over a range of compositions and substrate temperatures, we achieve phase separation on scales from 5 nm to 1 micron. The composite films exhibit simultaneous superconductivity and ferromagnetism. Transport measurements show that while the self-field Jc is reduced in the composites, the in-field Jc is greatly enhanced up to the 3 T saturation field of Dy. In one instance, the phase separation orders into stripes, leading to in-plane anisotropy in Jc.Comment: 7 pages, 7 figures. Matches the version published in SUST: Added one reference and some discussion in Section

Applications of environmental scanning electron microscopy to colloidal aggregation and film formation

info:eu-repo/semantics/publishe

Pure Spin Currents Driven by Colossal Spin-Orbit Coupling on Two-Dimensional Surface Conducting SrTiO3

Spin accumulation is generated by passing a charge current through a ferromagnetic layer and sensed by other ferromagnetic layers downstream. Pure spin currents can also be generated in which spin currents flow and are detected as a nonlocal resistance in which the charge current is diverted away from the voltage measurement point. Here, we report nonlocal spin-transport on two-dimensional surface-conducting SrTiO3 (STO) without a ferromagnetic spin-injector via the spin Hall effect (and inverse spin Hall effect). By applying magnetic fields to the Hall bars at different angles to the nonlocal spin-diffusion, we demonstrate an anisotropic spin-signal that is consistent with a Hanle precession of a pure spin current. We extract key transport parameters for surface-conducting STO, including: a spin Hall angle of gamma approximate to (0.25 +/- 0.05), a spin lifetime of tau similar to 49 ps, and a spin diffusion length of lambda(s) approximate to (1.23 +/- 0.7) mu m at 2 K

Multi-module microwave assembly for fast read-out and charge noise characterization of silicon quantum dots

International audienceFast measurements of quantum devices is important in areas such as quantum sensing, quantum computing and nanodevice quality analysis. Here, we develop a superconductor-semiconductor multi-module microwave assembly to demonstrate charge state readout at the state-of-the-art. The assembly consist of a superconducting readout resonator interfaced to a silicon-on-insulator (SOI) chiplet containing quantum dots (QDs) in a high-$\kappa$ nanowire transistor. The superconducting chiplet contains resonant and coupling elements as well as $LC$ filters that, when interfaced with the silicon chip, result in a resonant frequency $f=2.12$~GHz, a loaded quality factor $Q=680$, and a resonator impedance $Z=470$~$\Omega$. Combined with the large gate lever arms of SOI technology, we achieve a minimum integration time for single and double QD transitions of 2.77~ns and 13.5~ns, respectively. We utilize the assembly to measure charge noise over 9 decades of frequency up to 500~kHz and find a 1/$f$ dependence across the whole frequency spectrum as well as a charge noise level of 4~$\mu$eV/$\sqrt{\text{Hz}}$ at 1~Hz. The modular microwave circuitry presented here can be directly utilized in conjunction with other quantum device to improve the readout performance as well as enable large bandwidth noise spectroscopy, all without the complexity of superconductor-semiconductor monolithic fabrication

Parametric Amplifiers Based on Quantum Dots

International audienceJosephson parametric amplifiers (JPAs) approaching quantum-limited noise performance have been instrumental in enabling high fidelity readout of superconducting qubits and, recently, semiconductor quantum dots (QDs). We propose that the quantum capacitance arising in electronic two-level systems (the dual of Josephson inductance) can provide an alternative dissipationless nonlinear element for parametric amplification. We experimentally demonstrate phase-sensitive parametric amplification using a QD-reservoir electron transition in a CMOS nanowire split-gate transistor embedded in a 1.8 GHz superconducting lumped-element microwave cavity, achieving parametric gains of -3 to +3  dB, limited by Sisyphus dissipation. Using a semiclassical model, we find an optimized design within current technological capabilities could achieve gains and bandwidths comparable to JPAs, while providing complementary specifications with respect to integration in semiconductor platforms or operation at higher magnetic fields

Quantum Dot-Based Parametric Amplifiers

Josephson parametric amplifiers (JPAs) approaching quantum-limited noise performance have been instrumental in enabling high fidelity readout of superconducting qubits and, recently, semiconductor quantum dots (QDs). We propose that the quantum capacitance arising in electronic two-level systems (the dual of Josephson inductance) can provide an alternative dissipation-less non-linear element for parametric amplification. We experimentally demonstrate phase-sensitive parametric amplification using a QD-reservoir electron transition in a CMOS nanowire split-gate transistor embedded in a 1.8~GHz superconducting lumped-element microwave cavity, achieving parametric gains of -3 to +3 dB, limited by Sisyphus dissipation. Using a semi-classical model, we find an optimised design within current technological capabilities could achieve gains and bandwidths comparable to JPAs, while providing complementary specifications with respect to integration in semiconductor platforms or operation at higher magnetic fields

In Situ Observation of the Effect of Nitrogen on Carbon Nanotube Synthesis

In Situ Observation of the Effect of Nitrogen on Carbon Nanotube Synthesi