Self-aligned gates for scalable silicon quantum computing

Abstract

Silicon quantum dot spin qubits have great potential for application in large-scale quantum circuits as they share many similarities with conventional transistors that represent the prototypical example for scalable electronic platforms. However, for quantum dot formation and control, additional gates are required, which add to device complexity and, thus, hinder upscaling. Here, we meet this challenge by demonstrating the scalable integration of a multilayer gate stack in silicon quantum dot devices using self-alignment, which allows for ultra-small gate lengths and intrinsically perfect layer-to-layer alignment. We explore the prospects of these devices as hosts for hole spin qubits that benefit from electrically driven spin control via spin–orbit interaction. Therefore, we study hole transport through a double quantum dot and observe current rectification due to the Pauli spin blockade. The application of a small magnetic field leads to lifting of the spin blockade and reveals the presence of spin–orbit interaction. From the magnitude of a singlet-triplet anticrossing at a high magnetic field, we estimate a spin–orbit energy of ∼37μeV, which corresponds to a spin–orbit length of ∼48 nm. This work paves the way for scalable spin-based quantum circuits with fast, all-electrical qubit control.

Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots

“…In Fig. 2b), we also compare the hyperfine noise in DRA FinFETs and in state-of-the-art devices [10,35,36], where the fins are grown along the standard axes (SA) z [110] and y [100]. In this case, we estimate T SA 0 ≈ 0.2 − 0.6 µs depending on the direction of B, in reasonable agreement with experiments [10].…”

“…Strikingly, this issue is resolved in Si DRA FinFETs with triangular cross-section [10,[35][36][37], where the hyperfine sweet spots appear when B ⊥ x. In fact, as shown in Fig.…”

“…This decrease in noise can save two orders of magnitude of isotopic purification. Strikingly, by analyzing common designs, we find optimal working points in Si Fin field effect transistors (FinFETs) [10,35,36] where both hyperfine and charge noise [37] are suppressed simultaneously, strongly boosting the qubit coherence. Also, we examine the interplay between DRSOI and hyperfine interactions [38].…”

“…where ν is the isotopic abundance of the nuclear defects, N = √ 2πl z A ρ n 0 is the number of atoms in the dot, and A ρ is the area of the wire cross-section. In particular, for natural Si and Ge dots with N ≈ 10 4 atoms [10,35,36], we find τSi ≈ 0.36 µs and τGe ≈ 0.11 µs [47]. The dimensionless diagonal elements of Σ are and at l −1 SO = 0 they attain the values…”

Electrical control of the g tensor of the first hole in a silicon MOS quantum dot

“…The g tensor is the key parameter for studying the coupling of a spin-orbit state to a magnetic field [26][27][28][29][30][31][32][33]. However, most studies of the g tensor of hole quantum dots have been performed using devices that confine an unknown number of holes [34][35][36][37][38][39][40][41]. This has hindered the ability to understand hole-spin-qubit devices, since the number of holes is a primary factor influencing the orbital physics of the quantum dot [42].…”