  Quantum criticality, being important as an indicator of new quantum matters
emerging, is known to occur only at zero or low temperature. We find that a
quantum probe, if its coherence time is long, can detect quantum criticality at
infinitely high temperature. In particular, the echo control over a spin probe
can remove the thermal fluctuation effects and hence reveals the quantum
fluctuation effects. Probes with quantum coherence time of milliseconds or
seconds can be used to study emerging quantum orders that would occur at
extremely low temperatures of nano- or pico-Kelvin. This discovery establishes
a physical link between time and inverse temperature and provides a new route
to the wonderland of quantum matters.
