Probing Yang-Lee Edge Singularity by Central Spin Decoherence
  Yang-Lee edge singularities are the branch point of the free energy on the complex plane of physical parameters and were shown to be the simplest universality class of phase transitions. However, the Yang-Lee edge singularities have not been regarded as experimentally observable since they occur at complex physical parameters, which are unphysical. A recent discovery about the relation between partition functions and probe spin coherence makes it experimentally feasible to access the complex plane of physical parameters. However, how to extract the critical point and the critical exponent of Yang-Lee edge singularities in many-body systems, which occurs only at thermodynamic limit, has still been elusive. Here we show that the quantum coherence of a probe spin coupled to finite-size Ising-type spin systems presents universal scaling behavior near the Yang-Lee edge singularity. The finite-size scaling behavior of quantum coherence of the probe spin predicts that one can extract the critical point and the critical exponent of the Yang-Lee edge singularity of Ising-type spin system in the thermodynamic limit from the spin coherence measurement of the probe spin coupled to finite Ising-type spin systems. This finding provides a practical approach to studying the nature of Yang-Lee edge singularities of many-body systems. 
Bo-Bo Wei
cond-mat.stat-mech quant-ph