  In metals and semiconductors, an impurity spin is quantum entangled with and
thereby screened by surrounding conduction electrons at low temperatures,
called the Kondo screening cloud. Quantum confinement of the Kondo screening
cloud in a region, called a Kondo box, with a length smaller than the original
cloud extension length strongly deforms the screening cloud and provides a way
of controlling the entanglement. Here we realize such a Kondo box and develop
an approach to controlling and monitoring the entanglement. It is based on a
spin localized in a semiconductor quantum dot, which is screened by conduction
electrons along a quasi-one-dimensional channel. The box is formed between the
dot and a quantum point contact placed on a channel. As the quantum point
contact is tuned to make the confinement stronger, electron conductance through
the dot as a function of temperature starts to deviate from the known universal
function of the single energy scale, the Kondo temperature. Nevertheless, the
entanglement is monitored by the measured conductance according to our
theoretical development. The dependence of the monitored entanglement on the
confinement strength and temperature implies that the Kondo screening is
controlled by tuning the quantum point contact. Namely, the Kondo cloud is
deformed by the Kondo box in the region across the original cloud length. Our
findings offer a way of manipulating and detecting spatially extended quantum
many-body entanglement in solids by electrical means.
