Phys. Rev. A 75, 032109 (2007) [7 pages]Mixed-state fidelity and quantum criticality at finite temperatureReceived 30 November 2006; revised 8 January 2007; published 16 March 2007 We extend to finite temperature the fidelity approach to quantum phase transitions (QPTs). This is done by resorting to the notion of mixed-state fidelity that allows one to compare two density matrices corresponding to two different thermal states. By exploiting the same concept we also propose a finite-temperature generalization of the Loschmidt echo. Explicit analytical expressions of these quantities are given for a class of quasifree fermionic Hamiltonians. A numerical analysis is performed as well showing that the associated QPTs show their signatures in a finite range of temperatures. © 2007 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.75.032109
DOI:
10.1103/PhysRevA.75.032109
PACS:
03.65.Ud, 05.70.Jk, 05.45.Mt
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