Dr. Grazia Di Bello

Exploring dynamical quantum phase transitions and work extraction in an open two-qubit Rabi model

We investigate both the dynamical and thermodynamic properties of an open two-qubit Rabi model using state-of-the-art numerical methods [1]. By inducing a quench on the coupling between the qubits and the oscillator, the global system, including bath degrees of freedom, undergoes dynamical quantum phase transitions [2]. We identify two types of transitions, characterized by different critical exponents depending on the interactions and entanglement in the system. These transitions are marked by kinks in the rate function of the Loschmidt echo, occurring in the same range of parameters where a thermodynamic Berezinskii-Kosterlitz-Thouless transition occurs. Notably, the onset of these transitions is signaled not only by the bimodal character of the magnetization distribution but also by changes in the entanglement of the two qubits. These findings shed light on the complex dynamics of quantum phase transitions [3]. Additionally, given the insights obtained from this model and its relationship with quantum phase transitions, we aim to leverage them to extract work from the subsystem. Ergotropy, which quantifies the maximum extractable work from a quantum system, has recently garnered increasing attention for its relationship with many-body phenomena such as quantum phase transitions. In this context, we scrutinize the recent concept of local ergotropy [4], which measures work extraction ability in the presence of an uncontrollable surrounding environment. Specifically, we investigate the behavior of local ergotropy and its relative fluctuations across the previously discussed equilibrium quantum phase transition. We propose a realistic protocol encompassing charging, quasi-decoherence-free storage, and work extraction [5]. Our findings reveal that that high couplings to an external bath approximately double the local ergotropy immediately post-charging. Finally, we demonstrate that local ergotropy and its fluctuations can detect the quantum phase transition within the model. References: 1. G. De Filippis, A. de Candia, G. Di Bello, C. A. Perroni, L. M. Cangemi, A. Nocera, M. Sassetti, R. Fazio, and V. Cataudella, “Signatures of Dissipation Driven Quantum Phase Transition in Rabi Model”, Phys. Rev. Lett. 130, 210404 (2023). 2. M. Heyl, “Dynamical quantum phase transitions: A brief survey”, Europhys. Lett. 125, 26001 (2019). 3. G. Di Bello, A. Ponticelli, F. Pavan, V. Cataudella, G. De Filippis, A. de Candia, and C. A. Perroni, “Environment induced dynamical quantum phase transitions in two-qubit Rabi model”, arXiv preprint arXiv:2312.05697 (2023). 4. R. Salvia, G. De Palma, and V. Giovannetti, “Optimal local work extraction from bipartite quantum systems in the presence of Hamiltonian couplings”, Phys. Rev. A 107, 012405 (2023). 5. G. Di Bello, et al., “Local Ergotropy and its fluctuations across a dissipative quantum phase transition”, in prep.