L. Benini, P. Naldesi, R. A. Römer, T. Roscilde Quench dynamics of quasi-periodic systems exhibiting Rabi oscillations of two-level integrals of motion,
Ann. Phys. 435 (2021-12-01),
http://dx.doi.org/10.1016/j.aop.2021.168545 doi:10.1016/j.aop.2021.168545 (ID: 720781)
The elusive nature of localized integrals of motion (or l-bits) in disordered quantum systems lies at the core of some of their most prominent features, i.e. emergent integrability and lack of thermalization. Here, we study the quench dynamics of a one-dimensional model of spinless interacting fermions in a quasi-periodic potential with a localization–delocalization transition. Starting from an unentangled initial state, we show that in the strong disorder regime an important subset of the -bits can be explicitly identified with strongly localized two-level systems, associated with particles confined on two lattice sites. The existence of such subsystems forming an ensemble of nearly free -bits is found to dominate the short-time dynamics of experimentally relevant quantities, such as the Loschmidt echo and the particle imbalance. We investigate the importance of the choice of the initial state by developing a second quench protocol, starting from the ground-state of the model at different initial disorder strengths and monitoring the quench dynamics close to the delicate ETH-MBL transition regime.
G. Pecci, P. Naldesi, L. Amico, A. Minguzzi Probing the BCS-BEC crossover with persistent currents,
Phys. Rev. Research 3 (2021-09-14),
http://dx.doi.org/10.1103/PhysRevResearch.3.L032064 doi:10.1103/PhysRevResearch.3.L032064 (ID: 720782)
We study the persistent currents of an attractive Fermi gas confined in a tightly confining ring trap and subjected to an artificial gauge field all through the BCS-BEC crossover. At weak attractions, on the Bardeen-Cooper-Schrieffer (BCS) side, fermions display a parity effect in the persistent currents, i.e., their response to the gauge field is paramagnetic or diamagnetic depending on the number of pairs on the ring. At resonance and on the Bose-Einstein condensate (BEC) side of the crossover we find a doubling of the periodicity of the ground-state energy as a function of the artificial gauge field and disappearance of the parity effect, indicating that persistent currents can be used to infer the formation of tightly bound bosonic pairs. Our predictions can be accessed in ultracold atom experiments through noise interferograms.
L. Benini, P. Naldesi, R. A. Römer, T. Roscilde Loschmidt echo singularities as dynamical signatures of strongly localized phases,
New J. Phys. 23 (2021-02-18),
http://dx.doi.org/10.1088/1367-2630/abdf9d doi:10.1088/1367-2630/abdf9d (ID: 720780)
Quantum localization (single-body or many-body) comes with the emergence of local conserved quantities—whose conservation is precisely at the heart of the absence of transport through the system. In the case of fermionic systems and S = 1/2 spin models, such conserved quantities take the form of effective two-level systems, called l-bits. While their existence is the defining feature of localized phases, their direct experimental observation remains elusive. Here we show that strongly localized l-bits bear a dramatic universal signature, accessible to state-of-the-art quantum simulators, in the form of periodic cusp singularities in the Loschmidt echo following a quantum quench from a Néel/charge-density-wave state. Such singularities are perfectly captured by a simple model of Rabi oscillations of an ensemble of independent two-level systems, which also reproduces the short-time behavior of the entanglement entropy and the imbalance dynamics. In the case of interacting localized phases, the dynamics at longer times shows a sharp crossover to a faster decay of the Loschmidt echo singularities, offering an experimentally accessible signature of the interactions between l-bits.