  We describe optimization of a cryogenic magnetometer that uses nonlinear
kinetic inductance in superconducting nanowires as the sensitive element
instead of a superconducting quantum interference device (SQUID). The circuit
design consists of a loop geometry with two nanowires in parallel, serving as
the inductive section of a lumped LC resonator similar to a kinetic inductance
detector (KID). This device takes advantage of the multiplexing capability of
the KID, allowing for a natural frequency multiplexed readout. The Kinetic
Inductance Magnetometer (KIM) is biased with a DC magnetic flux through the
inductive loop. A perturbing signal will cause a flux change through the loop,
and thus a change in the induced current, which alters the kinetic inductance
of the nanowires, causing the resonant frequency of the KIM to shift. This
technology has applications in astrophysics, material science, and the medical
field for readout of Metallic Magnetic Calorimeters (MMCs), axion detection,
and magnetoencephalography (MEG).
