An exchange-based surface-code quantum computer architecture in silicon

Abstract

Phosphorus donor spins in silicon offer a number of promising characteristics for the implementation of robust qubits. Amongst various concepts for scale-up, the shared-control concept takes advantage of 3D scanning tunnelling microscope (STM) fabrication techniques to minimise the number of control lines, allowing the donors to be placed at the pitch limit of ≥30 nm, enabling dipole interactions. A fundamental challenge is to exploit the faster exchange interaction, however, the donor spacings required are typically 15 nm or less, and the exchange interaction is notoriously sensitive to lattice site variations in donor placement. This work presents a proposal for a fast exchange-based surface-code quantum computer architecture which explicitly addresses both donor placement imprecision commensurate with the atomic-precision fabrication techniques and the stringent qubit pitch requirements. The effective pitch is extended by incorporation of an intermediate donor acting as an exchange-interaction switch. We consider both global control schemes and a scheduled series of operations by designing GRAPE pulses for individual CNOTs based on coupling scenarios predicted by atomistic tight-binding simulations. The architecture is compatible with the existing fabrication capabilities and may serve as a blueprint for the experimental implementation of a full-scale fault-tolerant quantum computer based on donor impurities in silicon.

A scalable and fast artificial neural network syndrome decoder for surface codes

“…After years of theoretical developments, only recently have surface code experimental demonstrations, albeit at small scale, been reported on superconducting quantum devices [8,9]. Additionally, a number of theoretical proposals have also been reported to incorporate surface code error correction scheme in scalable semiconductor qubit systems [25][26][27] and superconducting quantum devices [28], indicating potential for larger sized demonstrations in the coming years. One of the promising characteristics of the surface code based error correction scheme is the associated high threshold which is 15-18% (≈0.5%) without (with) measurement errors [7,10,[29][30][31].…”

Calibrated decoders for experimental quantum error correction

“…An optimal choice of a code varies depending on the device and its noise properties [7]. Notable experimental implementations include NMR [8,9], ion traps [10][11][12][13], donors [14][15][16], quantum dots [17,18], and superconducting qubits [19][20][21][22][23]. Recent developments of high-fidelity mid-circuit measurements and resets of superconducting qubits have enabled the preparation and repeated stabilization of logical states [24][25][26]; demonstrations of such quantum memories with enhanced lifetimes have been limited by, among other reasons, a combination of gate and measurement cross-talk.…”