The quantum Fisher information has gained popularity due to its versatility and its multi-purposed nature. For example, in quantum metrology the quantum Fisher information is used to quantify the maximal accuracy for which a parameter may be estimated and in quantum information theory it is used as a witness of multipartite entanglement. In condensed matter physics the quantum Fisher information has been used to study phase transitions, primarily in equilibrium quantum many body systems. In this work we study the quantum Fisher information for a p+ip superfluid both in equilibrium and out of equilibrium. In equilibrium the p+ip superfluid exhibits a topological quantum phase transition between a topological weak pairing phase (BCS) and a topologically trivial strong pairing phase (BEC). After an instantaneous interaction quench, the long time asymptotic state of p+ip superfluid is characterized by three different dynamical phases and within each phase the behaviour of the asymptotic order parameter changes. In equilibrium, we find that the QFI calculated with respect to particle number using the BCS ground-state fails to probe the topological quantum phase transition. On the other hand, in our non-equilibrium treatment we find that by quenching the system out of equilibrium the quantum Fisher information can be used to extract topological information of the pre-quench state and the character of the energy dispersion of the post-quench state. Our results therefore suggest that by introducing a quantum quench the quantum Fisher information is able to extract useful information and does not rely on the choice of operator, as opposed to the equilibrium case.The quantum Fisher information has gained popularity due to its versatility and its multi-purposed nature. For example, in quantum metrology the quantum Fisher information is used to quantify the maximal accuracy for which a parameter may be estimated and in quantum information theory it is used as a witness of multipartite entanglement. In condensed matter physics the quantum Fisher information has been used to study phase transitions, primarily in equilibrium quantum many body systems. In this work we study the quantum Fisher information for a p+ip superfluid both in equilibrium and out of equilibrium. In equilibrium the p+ip superfluid exhibits a topological quantum phase transition between a topological weak pairing phase (BCS) and a topologically trivial strong pairing phase (BEC). After an instantaneous interaction quench, the long time asymptotic state of p+ip superfluid is characterized by three different dynamical phases and within each phase the behaviour of the asymptotic order parameter changes. In equilibrium, we find that the QFI calculated with respect to particle number using the BCS ground-state fails to probe the topological quantum phase transition. On the other hand, in our non-equilibrium treatment we find that by quenching the system out of equilibrium the quantum Fisher information can be used to extract topological information of the pre-quench state and the character of the energy dispersion of the post-quench state. Our results therefore suggest that by introducing a quantum quench the quantum Fisher information is able to extract useful information and does not rely on the choice of operator, as opposed to the equilibrium case.

Jan 1, 20260 citations

Quantum quenching through a topological phase transition in a system with open boundaries

Vasudha Shivamoggi, Smitha Vishveshwara, Diptiman Sen

Bulletin of the American Physical SocietyMar 3, 20140 citations

Quantum Fisher information in a quenched $p + ip$ superfluidQuantum Fisher information in a quenched $p + ip$ superfluid

Stelio Varrone, Yunxiang Liao

The quantum Fisher information (QFI) is widely used to characterize quantum phases and transitions, but its diagnostic power sometimes relies on selecting special generators based on prior knowledge of the underlying physics. We ask whether this requirement can be relaxed in nonequilibrium systems by studying the QFI of the long-time asymptotic state of a two-dimensional p+ip superfluid following an instantaneous quench of the coupling strength, using the particle number within a large subextensive subsystem as the generator. In equilibrium, the ground-state QFI is continuous across the topological transition between the weak-pairing BCS and the strong-pairing BEC phases, showing no direct signature of the transition. After the quench, however, the QFI associated with the same generator distinguishes the three dynamical phases and can encode the topology of the pre-quench state. In phase I, with a vanishing order parameter, the QFI Fourier spectrum consists of a single zero-frequency spike determined by the nonequilibrium distribution function. In phase II, with a constant nonzero order parameter, the QFI spectrum contains a zero-frequency spike and two continua separated by a gap set by the minimum asymptotic quasiparticle energy. The continuum edge behavior reveals whether this minimum occurs at zero or finite momentum. In the former case, the spectral weight vanishes at the edge, with the sign just inside the continuum encoding the pre-quench topology for large subsystem. In phase III, with a time-periodic order parameter, the QFI spectrum exhibits discrete peaks at integer multiples of the oscillation frequency, together with continua associated with the Floquet quasienergy spectrum. Our results show that driving the system out of equilibrium can enhance the diagnostic power of the QFI for a standard physical observable, revealing information inaccessible in equilibrium.The quantum Fisher information (QFI) is widely used to characterize quantum phases and transitions, but its diagnostic power sometimes relies on selecting special generators based on prior knowledge of the underlying physics. We ask whether this requirement can be relaxed in nonequilibrium systems by studying the QFI of the long-time asymptotic state of a two-dimensional p+ip superfluid following an instantaneous quench of the coupling strength, using the particle number within a large subextensive subsystem as the generator. In equilibrium, the ground-state QFI is continuous across the topological transition between the weak-pairing BCS and the strong-pairing BEC phases, showing no direct signature of the transition. After the quench, however, the QFI associated with the same generator distinguishes the three dynamical phases and can encode the topology of the pre-quench state. In phase I, with a vanishing order parameter, the QFI Fourier spectrum consists of a single zero-frequency spike determined by the nonequilibrium distribution function. In phase II, with a constant nonzero order parameter, the QFI spectrum contains a zero-frequency spike and two continua separated by a gap set by the minimum asymptotic quasiparticle energy. The continuum edge behavior reveals whether this minimum occurs at zero or finite momentum. In the former case, the spectral weight vanishes at the edge, with the sign just inside the continuum encoding the pre-quench topology for large subsystem. In phase III, with a time-periodic order parameter, the QFI spectrum exhibits discrete peaks at integer multiples of the oscillation frequency, together with continua associated with the Floquet quasienergy spectrum. Our results show that driving the system out of equilibrium can enhance the diagnostic power of the QFI for a standard physical observable, revealing information inaccessible in equilibrium.

cond-mat.quant-gasCross-listedarXiv:2608.21164Aug 24, 20260 citations

Quantum Fisher information in a quenched

p + ip

superfluid