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Register a new userSingle-electron control in a foundry-fabricated two-dimensional qubit array
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Silicon spin qubits have achieved high-fidelity one- and two-qubit gates, above error correction thresholds, promising an industrial route to fault-tolerant quantum computation. A significant next step for the development of scalable multi-qubit processors is the operation of foundry-fabricated, extendable two-dimensional (2D) arrays. In gallium arsenide, 2D quantum-dot arrays recently allowed coherent spin operations and quantum simulations. In silicon, 2D arrays have been limited to transport measurements in the many-electron regime. Here, we operate a foundry-fabricated silicon 2x2 array in the few-electron regime, achieving single-electron occupation in each of the four gate-defined quantum dots, as well as reconfigurable single, double, and triple dots with tunable tunnel couplings. Pulsed-gate and gate-reflectometry techniques permit single-electron manipulation and single-shot charge readout, while the two-dimensionality allows the spatial exchange of electron pairs. The compact form factor of such arrays, whose foundry fabrication can be extended to larger 2xN arrays, along with the recent demonstration of coherent spin control and readout, paves the way for dense qubit arrays for quantum computation and simulation.
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Photonic crystals use periodic structures to create forbidden frequency regions for optical wave propagation, that allow for the creation and integration of complex optical functions in small footprint devices. Such strategy has also been successfully applied to confine mechanical waves and to explore their interaction with light in the so-called optomechanical cavities. Because of their challenging design, these cavities are traditionally fabricated using dedicated high-resolution electron-beam lithography tools that are inherently slow, limiting this solution to small-scale applications or research. Here we show how to overcome this problem by using a deep-UV photolithography process to fabricate optomechanical crystals on a commercial CMOS foundry. We show that a careful design of the photonic crystals can withstand the limitations of the photolithography process, producing cavities with measured intrinsic optical quality factors as high as $Q_{i}=(1.21pm0.02)times10^{6}$. Optomechanical crystals are also created using phononic crystals to tightly confine the sound waves within the optical cavity that results in a measured vacuum optomechanical coupling rate of $g_{0}=2pitimes(91pm4)$ kHz. Efficient sideband cooling and amplification are also demonstrated since these cavities are in the resolved sideband regime. Further improvement in the design and fabrication process suggest that commercial foundry-based optomechanical cavities could be used for quantum ground-state cooling.
Quantum dots fabricated using techniques and materials that are compatible with semiconductor manufacturing are promising for quantum information processing. While great progress has been made toward high-fidelity control of quantum dots positioned in a linear arrangement, scalability along two dimensions is a key step toward practical quantum information processing. Here we demonstrate a two-dimensional quantum dot array where each quantum dot is tuned to single-charge occupancy, verified by simultaneous measuring with two integrated radio frequency charge sensors. We achieve this by using planar germanium quantum dots with low disorder and small effective mass, allowing the incorporation of dedicated barrier gates to control the coupling of the quantum dots. We demonstrate hole charge filling consistent with a Fock-Darwin spectrum and show that we can tune single-hole quantum dots from isolated quantum dots to strongly exchange coupled quantum dots. These results motivate the use of planar germanium quantum dots as building blocks for quantum simulation and computation.
We demonstrate trapping in a surface-electrode ion trap fabricated in a 90-nm CMOS (complementary metal-oxide-semiconductor) foundry process utilizing the top metal layer of the process for the trap electrodes. The process includes doped active regions and metal interconnect layers, allowing for co-fabrication of standard CMOS circuitry as well as devices for optical control and measurement. With one of the interconnect layers defining a ground plane between the trap electrode layer and the p-type doped silicon substrate, ion loading is robust and trapping is stable. We measure a motional heating rate comparable to those seen in surface-electrode traps of similar size. This is the first demonstration of scalable quantum computing hardware, in any modality, utilizing a commercial CMOS process, and it opens the door to integration and co-fabrication of electronics and photonics for large-scale quantum processing in trapped-ion arrays.
A new method to fabricate non-superconducting mesoscopic tunnel junctions by oxidation of Ti is presented. The fabrication process uses conventional electron beam lithography and shadow deposition through an organic resist mask. Superconductivity in Ti is suppressed by performing the deposition under a suitable background pressure. We demonstrate the method by making a single electron transistor which operated at $T < 0.4$ K and had a moderate charge noise of $2.5 times 10^{-3}$ e/$sqrt{mathrm{Hz}}$ at 10 Hz. Based on nonlinearities in the current-voltage characteristics at higher voltages, we deduce the oxide barrier height of approximately 110 mV.
Fluid dynamics is one of the cornerstones of modern physics and has recently found applications in the transport of electrons in solids. In most solids electron transport is dominated by extrinsic factors, such as sample geometry and scattering from impurities. However in the hydrodynamic regime Coulomb interactions transform the electron motion from independent particles to the collective motion of a viscous `electron fluid. The fluid viscosity is an intrinsic property of the electron system, determined solely by the electron-electron interactions. Resolving the universal intrinsic viscosity is challenging, as it only affects the resistance through interactions with the sample boundaries, whose roughness is not only unknown but also varies from device to device. Here we eliminate all unknown parameters by fabricating samples with smooth sidewalls to achieve the perfect slip boundary condition, which has been elusive both in molecular fluids and electronic systems. We engineer the device geometry to create viscous dissipation and reveal the true intrinsic hydrodynamic properties of a 2D system. We observe a clear transition from ballistic to hydrodynamic electron motion, driven by both temperature and magnetic field. We directly measure the viscosity and electron-electron scattering lifetime (the Fermi quasiparticle lifetime) over a wide temperature range without fitting parameters, and show they have a strong dependence on electron density that cannot be explained by conventional theories based on the Random Phase Approximation.
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