Publications Piero NALDESI

2023

Preprint

• D. González-Cuadra, D. Bluvstein, M. Kalinowski, C. R. Kaubrügger, N. Maskara, P. Naldesi, T. Zache, A. Kaufman, M. Lukin, H. Pichler, B. Vermersch, J. Ye, P. Zoller Fermionic quantum processing with programmable neutral atom arrays, (2023-03-13), arXiv:2303.06985 arXiv:2303.06985 (ID: 721066) Toggle Abstract
  Simulating the properties of many-body fermionic systems is an outstanding computational challenge relevant to material science, quantum chemistry, and particle physics. Although qubit-based quantum computers can potentially tackle this problem more efficiently than classical devices, encoding non-local fermionic statistics introduces an overhead in the required resources, limiting their applicability on near-term architectures. In this work, we present a fermionic quantum processor, where fermionic models are locally encoded in a fermionic register and simulated in a hardware-efficient manner using fermionic gates. We consider in particular fermionic atoms in programmable tweezer arrays and develop different protocols to implement non-local tunneling gates, guaranteeing Fermi statistics at the hardware level. We use this gate set, together with Rydberg-mediated interaction gates, to find efficient circuit decompositions for digital and variational quantum simulation algorithms, illustrated here for molecular energy estimation. Finally, we consider a combined fermion-qubit architecture, where both the motional and internal degrees of freedom of the atoms are harnessed to efficiently implement quantum phase estimation, as well as to simulate lattice gauge theory dynamics.

2022

Preprint

• P. Naldesi, A. Elben, A. Minguzzi, D. Clement, Peter Zoller, B. Vermersch Fermionic correlation functions from randomized measurements in programmable atomic quantum devices, (2022-05-02), arXiv:2205.00981 arXiv:2205.00981 (ID: 720886) Toggle Abstract
  We provide a measurement protocol to estimate 2- and 4-point fermionic correlations in ultra-cold atom experiments. Our approach is based on combining random atomic beam splitter operations, which can be realized with programmable optical landscapes, with high-resolution imaging systems such as quantum gas microscopes. We illustrate our results in the context of the variational quantum eigensolver algorithm for solving quantum chemistry problems.

2021

Articles

• 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) Toggle Abstract
  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) Toggle Abstract
  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) Toggle Abstract
  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.

Preprint

• G. Pecci, P. Naldesi, A. Minguzzi, L. Amico The phase of a degenerate Fermi gas, (2021-05-21), arXiv:2105.10408 arXiv:2105.10408 (ID: 720783) Toggle Abstract
  In quantum mechanics, each particle is described by a complex valued wave function characterized by amplitude and phase. When many particles interact each other, cooperative phenomena give rise to a quantum many-body state with a specific quantum coherence. What is the interplay between particle's phase coherence and many-body quantum coherence? Over the years, such question has been object of profound analysis in quantum physics. Here, we demonstrate how state of the art quantum technology allows to explore the question operatively. To this end, we study the time-dependent interference formed by releasing an interacting degenerate Fermi-gas from a specific matter-wave circuit in an effective magnetic field. Particle phase coherence, indicated by the first-order correlator, and many-body quantum coherence, indicated by the noise correlator, are displayed as distinct features of the interferogram. Particle phase coherence produces spiral interference of the Fermi orbitals at intermediate times. Many-body quantum coherence emerges at long times. The coupling between particles coherence and many-body coherence is reflected in a specific dependence of the interference pattern on the effective magnetic field.