  Semiconductor spin qubits offer a unique opportunity for scalable quantum
computation by leveraging classical transistor technology. Hole spin qubits
benefit from fast all-electrical qubit control and sweet spots to counteract
charge and nuclear spin noise. The demonstration of a two-qubit quantum gate in
a silicon fin field-effect transistor, that is, the workhorse device of today's
semiconductor industry, has remained an open challenge. Here, we demonstrate a
controlled rotation two-qubit gate on hole spins in an industry-compatible
device. A short gate time of 24 ns is achieved. The quantum logic exploits an
exchange interaction that can be tuned from above 500 MHz to close-to-off.
Significantly, the exchange is strikingly anisotropic. By developing a general
theory, we show that the anisotropy arises as a consequence of a strong
spin-orbit interaction. Upon tunnelling from one quantum dot to the other, the
spin is rotated by almost 90 degrees. The exchange Hamiltonian no longer has
Heisenberg form and is engineered in such a way that there is no trade-off
between speed and fidelity of the two-qubit gate. This ideal behaviour applies
over a wide range of magnetic field orientations rendering the concept robust
with respect to variations from qubit to qubit. Our work brings hole spin
qubits in silicon transistors a step closer to the realization of a large-scale
quantum computer.
