Quantum links for large-scale spin qubit architecturesAndre Saraiva*

Provably useful quantum computations require tens of millions of qubits to be operated with high fidelity in order to implement quantum error correction. Wiring qubits individually will not be scalable, such that it will be necessary to combine some in loco control electronics near the qubits and some control signals that can be shared among multiple qubits, using a wordline/bitline scheme. This creates a requirement for reducing the density of qubits to allow room for this interspersed electronics.

This reduction in density is made possible through coherent quantum links connecting these modules of qubits within the same chip. Multiple technologies for high-fidelity remote coupling between spin qubits have been developed over the years. We will cover three technologies that we recently explored in the context of CMOS electrostatic quantum dots. We will discuss some ideas for spin-photon conversion schemes, besides simulations and early experimental results for multielectron coupler dots (jellybean dots).

A more detailed discussion will be devoted to a technology in which we have achieved most success: high-fidelity remote coupling using coherent transfer of spin qubits by tunnelling in a chain of quantum dots. Initial demonstrations exceeded 99% coherence transfer fidelity and 99.9% polarity transfer fidelity. With devices designed for optimal shuttling of electrons, even higher number might be achievable.

We will finalise mapping pros and cons of each quantum linking technology and how it might help shape the face of large-scale quantum error corrected processors.