Highly tunable exchange in donor qubits in silicon

In this article we have investigated the electrical control of the exchange coupling (J) between donor-bound electrons in silicon with a detuning gate bias, crucial for the implementation of the two-qubit gate in a silicon quantum computer. We found that the asymmetric 2P–1P system provides a highly tunable exchange curve with mitigated J-oscillation, in which 5 orders of magnitude change in the exchange coupling can be achieved using a modest range of electric field (3 MV/m) for ~15-nm qubit separation. Compared with the barrier gate control of exchange in the Kane qubit, the detuning gate design reduces the gate density by a factor of ~2. By combining large-scale atomistic tight-binding method with a full configuration interaction technique, we captured the full two-electron spectrum of gated donors, providing state-of-the-art calculations of exchange energy in 1P–1P and 2P–1P qubits. Researchers in the United States and Australia propose an improved design for quantum computing in silicon. The team, led by researchers at Purdue University, found that a design consisting of two paired phosphorous donor atoms in silicon interacting with another nearby phosphorous atom provides a stable and easy-to-control way to realize highly integrated qubits in silicon. Although donor atoms in silicon promise a high density integration similar to the integrated electronic circuits in conventional silicon electronics, conventional qubits based on two interacting phosphorous atoms are vulnerable to fabrication errors. In contrast, the proposed system based on pairs of two plus one phosphorous atoms provides greater stability against fabrication errors, as well as an enhanced tunability of their interactions, supporting the practical realization of quantum computing architectures in silicon.