Loschmidt Echo of Far-From-Equilibrium Fermionic Superfluids

Abstract

Non-analyticities in the logarithm of the Loschmidt echo, known as dynamical quantum phase transitions [DQPTs], are a recently introduced attempt to classify the myriad of possible phenomena which can occur in far from equilibrium closed quantum systems. In this work, we analytically investigate the Loschmidt echo in nonequilibrium $s$-wave and topological $p_x+i{p}_y$ fermionic superfluids. We find that the presence of non-analyticities in the echo is not invariant under global rotations of the superfluid phase. We remedy this deficiency by introducing a more general notion of a grand canonical Loschmidt echo. Overall, our study shows that DQPTs are not a good indicator for the long time dynamics of an interacting system. In particular, there are no DQPTs to tell apart distinct dynamical phases of quenched BCS superconductors. Nevertheless, they can signal a quench induced change in the topology and also keep track of solitons emerging from unstable stationary states of a BCS superconductor.

24 pages, 12 figures

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Cited by in corpus (4)

• Metamorphic dynamical quantum phase transition in double-quench processes at finite temperatures
• Dynamical quantum phase transitions in the one-dimensional extended Fermi-Hubbard model
• Singularities in the Loschmidt echo of quenched topological superconductors
• Loschmidt echo and Momentum Distribution in a Kitaev Spin Chain