  As a foundation of statistical physics, Lee and Yang in 1952 proved that the
partition functions of thermal systems can be zero at certain points (called
Lee-Yang zeros) on the complex plane of temperature. In the thermodynamic
limit, the Lee-Yang zeros approach to real numbers at the critical temperature.
However, the imaginary Lee-Yang zeros have not been regarded as experimentally
observable since they occur at imaginary field or temperature, which are
unphysical. Here we show that the coherence of a probe spin weakly coupled to a
many-body system presents zeros as a function of time that are one-to-one
mapped to the Lee-Yang zeros of the many-body system. In the thermodynamic
limit, of which the Lee-Yang zeros form a continuum, the probe spin coherence
presents a sudden death at the edge singularities of the Lee-Yang zeros. By
measuring the probe spin coherence, one can directly reconstruct the partition
function of a many-body system. These discoveries establish a profound relation
between two most fundamental quantities in the physical world, time and
temperature, and also provide a universal approach to studying interacting
many-body systems through measuring coherence of only one probe spin (or one
qubit in quantum computing).
