  Nonreciprocal microwave routing plays a crucial role for measuring quantum
circuits, and allows for realizing cascaded quantum systems for generating and
stabilizing entanglement between non-interacting qubits. The most commonly used
tools for implementing directionality are ferrite-based circulators. These
devices are versatile, but suffer from excess loss, a large footprint, and
fixed directionality. For utilizing nonreciprocity in scalable quantum circuits
it is desirable to develop efficient integration of low-loss and in-situ
controllable directional elements. Here, we report the design and experimental
realization of a controllable directional interface that may be integrated
directly with superconducting qubits. In the presented device, nonreciprocity
is realized through a combination of interference and phase-controlled
parametric pumping. We have achieved a maximum directionality of around 30\,dB,
and the performance of the device is predicted quantitatively from independent
calibration measurements. Using the excellent agreement of model and
experiment, we predict that the circuit will be useable as a chiral qubit
interface with inefficiencies at the one-percent level or below. Our work
provides a route toward isolator-free qubit readout schemes and high-fidelity
entanglement generation in all-to-all connected networks of superconducting
quantum devices.
