  System scalability is fundamental for large-scale quantum computers (QCs) and
is being pursued over a variety of hardware platforms. For QCs based on trapped
ions, architectures such as the quantum charge-coupled device (QCCD) are used
to scale the number of qubits on a single device. However, the number of ions
that can be hosted on a single quantum computing module is limited by the size
of the chip being used. Therefore, a modular approach is of critical importance
and requires quantum connections between individual modules. Here, we present
the demonstration of a quantum matter-link in which ion qubits are transferred
between adjacent QC modules. Ion transport between adjacent modules is realised
at a rate of 2424$\,$s$^{-1}$ and with an infidelity associated with ion loss
during transport below $7\times10^{-8}$. Furthermore, we show that the link
does not measurably impact the phase coherence of the qubit. The quantum
matter-link constitutes a practical mechanism for the interconnection of QCCD
devices. Our work will facilitate the implementation of modular QCs capable of
fault-tolerant utility-scale quantum computation.
