We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity. A quality factor Q = 5,400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams and a charge-cavity coupling rate g c /2π = 23 MHz. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.

The conduction and valence band offsets between amorphous LaAlO3 and silicon have been determined from x-ray photoelectron spectroscopy measurements. These films, which are free of interfacial SiO2, were made by molecular-beam deposition. The band line-up is type I with measured band offsets of 1.8±0.2 eV for electrons and 3.2±0.1 eV for holes. The band offsets are independent of the doping concentration in the silicon substrate as well as the amorphous LaAlO3 film thickness. These amorphous LaAlO3 films have a bandgap of 6.2±0.1 eV.

Electron spins in silicon have long coherence times [1][2][3][4][5][6] and are a promising qubit platform [7,8]. However, electric field noise in semiconductors poses a challenge for most single-and multi-qubit operations in quantum-dot spin qubits [4,9,10]. Here, we investigate the dependence of lowfrequency charge noise spectra on temperature and aluminum-oxide gate dielectric thickness in Si/SiGe quantum dots with overlapping gates. We find that charge noise increases with aluminum oxide thickness. We also find strong dot-to-dot variations in the temperature dependence of the noise magnitude and spectrum. These findings suggest that each quantum dot experiences noise caused by a distinct ensemble of two-level systems, each of which has a non-uniform distribution of thermal activation energies. Taken together, our results suggest that charge noise in Si/SiGe quantum dots originates at least in part from a non-uniform distribution of two-level systems near the surface of the semiconductor.

Solid state quantum processors based on spins in silicon quantum dots are emerging as a powerful platform for quantum information processing [1][2][3]. High fidelity single-and two-qubit gates have recently been demonstrated [2][3][4][5][6] and large extendable qubit arrays are now routinely fabricated [7,8]. However, two-qubit gates are mediated through nearest-neighbor exchange interactions [1,9], which require direct wavefunction overlap. This limits the overall connectivity of these devices and is a major hurdle to realizing error correction [10], quantum random access memory [11], and multi-qubit quantum algorithms [12]. To extend the connectivity, qubits can be shuttled around a device using quantum SWAP gates, but phase coherent SWAPs have not yet been realized in silicon devices [2][3][4][5][6]. Here, we demonstrate a new single-step resonant SWAP gate. We first use the gate to efficiently initialize and readout our double quantum dot. We then show that the gate can move spin eigenstates in 100 ns with average fidelityF (p) SWAP = 98 %. Finally, the transfer of arbitrary two-qubit product states is benchmarked using state tomography and Clifford randomized benchmarking [5,13], yielding an average fidelity ofF (c) SWAP = 84 % for gate operation times of ∼300 ns. Through coherent spin transport, our resonant SWAP gate enables the coupling of non-adjacent qubits, thus paving the way to large scale experiments using silicon spin qubits.In this work, we use two sites of a quadruple quantum dot fabricated on a 28 Si/SiGe heterostructure [inset of Fig. 1(a)] [8]. Electric dipole spin resonance (EDSR) [14,15] enables single-spin control and an on-chip micromagnet detunes the frequency of each spin to enable site-selective control [8,16]. For demonstration purposes, we use two dots in the device with qubits accumulated under plunger gates P 3 and P 4 . We hereafter refer to the two qubits as Q 3 and Q 4 , respectively. The charge stability diagram of this DQD is shown in Fig. 1(a) and quantum control is performed in the (N i , N i+1 ) = (1, 1) charge configuration, where N i denotes the number of electrons on dot i. We measure the state of Q 4 through spin-selective tunneling to a drain reservoir accumulated beneath gate D 3 [17].There are two modes of operation for the resonant SWAP gate demonstrated in this Letter. First, a projection-SWAP can be used to transfer spin eigenstates Figure 1. (a) Charge stability map for a DQD formed using sites 3 and 4 in the quadruple dot array (inset). Quantum control is performed near the center of the (1,1) charge stability region as denoted by the green circle. Readout of dot 4 is performed at the (1,0)-(1,1) charge transition denoted by the blue triangle. (b) The typical measurement cycle is shown for controlling and reading out two quantum dots. In panel A, the qubits are manipulated and in panel B Q4 is read out through spin-selective tunneling -leaving the qubit in the |↓ state. In panel C, the exchange interaction J34 between Q3 and Q4 is modulated (through modulation of...

Amorphous LaAlO3 thin films have been deposited by molecular beam deposition directly on silicon without detectable oxidation of the underlying substrate. We have studied these abrupt interfaces by Auger electron spectroscopy, high-resolution transmission electron microscopy, medium-energy ion scattering, transmission infrared absorption spectroscopy, and x-ray photoelectron spectroscopy. Together these techniques indicate that the films are fully oxidized and have less than 0.2 Å of SiO2 at the interface between the amorphous LaAlO3 and silicon. These heterostructures are being investigated for alternative gate dielectric applications and provide an opportunity to control the interface between the silicon and the gate dielectric.