We report a pre-registered observation of quantum many-body scar revivals in the one-dimensional PXP model, executed as Trotterized digital quantum simulation on a 156-qubit superconducting processor (IBM ibm_fez). Preparing the Neel-ordered product states |Z2>, |Z3>, and |Z4> on N=12 qubits with periodic boundary conditions and evolving under a first-order Trotter decomposition of the PXP Hamiltonian, we measure the return probability P(t) at five times up to t = 4.8. The scarred state |Z2> shows a return probability of 0.0710 ± 0.0041 at t = 4.8, while the thermalizing control |Z4>, evolved through an identical-depth circuit, shows 0.0008 ± 0.0004. The differential signal constitutes a 17.2-sigma observation of selective revival, exceeding our pre-registered 3-sigma criterion. Because both states traverse identical circuit depths, hardware noise affects them equally and the difference isolates the physical scar signature.
We report a pre-registered observation of quantum many-body scar revivals in the one-dimensional PXP model, executed as Trotterized digital quantum simulation on a 156-qubit superconducting processor (IBM ibm_fez). Preparing the Neel-ordered product states |Z2>, |Z3>, and |Z4> on N=12 qubits with periodic boundary conditions and evolving under a first-order Trotter decomposition of the PXP Hamiltonian, we measure the return probability P(t) at five times up to t = 4.8. The scarred state |Z2> shows a return probability of 0.0710 ± 0.0041 at t = 4.8, while the thermalizing control |Z4>, evolved through an identical-depth circuit, shows 0.0008 ± 0.0004. The differential signal constitutes a 17.2-sigma observation of selective revival, exceeding our pre-registered 3-sigma criterion. Because both states traverse identical circuit depths, hardware noise affects them equally and the difference isolates the physical scar signature.
We report, to our knowledge, the first observation of asymptotic quantum many-body scars (AQMBS) on a superconducting processor. Implementing the periodically-driven PVBS model of Logarić, Goold, and Dooley at g = 1 as a digital Floquet brickwork circuit on IBM's 156-qubit ibm_fez, we prepare the scar-adjacent state |A₁⟩ on N = 8, 12, 16, 20 qubits and measure the normalized magnetization M_Z(t)/M_Z(0) over ten Floquet steps. The decay slows dramatically with system size — the defining AQMBS signature — with pairwise size-gap significances of 7.5σ, 4.1σ, and 5.8σ at t = 10 (the last from a pre-registered combined analysis of two independent runs), against a pre-registered 3σ criterion per gap. The thermalizing (|1⟩^⊗N) control behaves as predicted at every size; the stationary (|V⟩ = |0⟩^⊗N) control is flat across N but decays further than first modeled — a miscalibrated bar documented and corrected openly in §3. AQMBS were previously observed only once, on a trapped-ion simulator; no superconducting-qubit realization existed in the literature. All three hardware runs were pre-registered before execution, with frozen success criteria; two initial runs missed the bar (2.2σ and 2.98σ on the tightest gap) and were reported as misses before a powered top-up run closed the detection.
Quantum many-body scars are energy eigenstates which fail to reproduce thermal expectation values of local observables, in systems where the rest of the many-body spectrum fulfils eigenstate thermalization. Experimental observation of quantum many-body scars has so far been limited to models with multiple scar states evenly spaced in energy. It is thus an interesting question whether even single isolated scars, which theoretically embody the weakest possibile violation of eigenstate thermalization and may be thought to have no detectable impact in experiments, can leave a trace in measurable quantities. Moreover, single scars offer an interesting scenario for exploring the connection between quantum many-body scars and the original notion of scarring in quantum dynamical systems theory. Here we propose protocols to observe single scars in architectures of fixed-frequency, fixed-coupling superconducting qubits. We first adapt known models possessing the desired features into a form particularly suited for the experimental platform. We develop protocols for the implementation of these models, through trotterized sequences of two-qubit cross-resonance interactions, and verify the existence of the approximate scar state in the stroboscopic effective Hamiltonian. Since a single scar cannot be detected from coherent revivals in the dynamics, differently from towers of scar states, we propose and numerically investigate alternative and experimentally-accessible signatures. These include the dynamical response of the scar to local state deformations, to controlled noise, and to the resolution of the Lie-Suzuki-Trotter digitization.
Persistent revivals recently observed in Rydberg atom simulators have challenged our understanding of thermalization and attracted much interest to the concept of quantum many-body scars (QMBSs). QMBSs are non-thermal highly excited eigenstates that coexist with typical eigenstates in the spectrum of many-body Hamiltonians, and have since been reported in multiple theoretical models, including the so-called PXP model, approximately realized by Rydberg simulators. At the same time, questions of how common QMBSs are and in what models they are physically realized remain open. In this Letter, we demonstrate that QMBSs exist in a broader family of models that includes and generalizes PXP to longer-range constraints and states with different periodicity. We show that in each model, multiple QMBS families can be found. Each of them relies on a different approximate su(2) algebra, leading to oscillatory dynamics in all cases. However, in contrast to the PXP model, their observation requires launching dynamics from weakly entangled initial states rather than from a product state. QMBSs reported here may be experimentally probed using Rydberg atom simulator in the regime of longer-range Rydberg blockades.
The PXP model hosts a special set of nonergodic states, referred to as quantum many-body scars. One of the consequences of quantum scarring is the periodic revival of the wave function fidelity. It has been reported that quantum fidelity revival occurs in the PXP model for certain product states, and periodic driving of the chemical potential can enhance the magnitude of quantum revival and can even change the frequencies of revival showing the subharmonic response. Although the effect of the periodic driving in the PXP model has been studied in the limit of certain perturbative regimes, the general mechanism of such enhanced revival and frequency change has been barely studied. In this paper, we investigate how periodic driving in the PXP model can systematically control the fidelity revival. Particularly, focusing on a product state called the N\'eel state, we analyze the condition of driving to enhance the magnitude of revival or change the frequencies of revival. To clarify the reason for such control, we consider the similarities between the PXP model and the free spin-1/2 model in graph theoretical analysis and show that the quantum fidelity feature in the PXP model is well explained by the free spin-1/2 model. In addition, under a certain limit of the driving parameters, an analytic approach to explain the main features of the fidelity revival is also applied. Our results give insight into the scarring nature of the periodically driven PXP model and pave the way to understand the (sub)harmonic responses in these models and controls thereof.
We investigate the stability of quantum many-body scars under perturbations, within the PXP model. We numerically compute the fidelity and average correlations to monitor the state evolution and to identify revivals. The results indicate that, on the one hand, the entanglement entropy of PXP scars exhibit great sensitivity, in the sense that their profile approaches the ones expected for thermal states already for very small perturbations. On the other hand, other scar signatures, such as the revivals of states having large overlap with scars, show remarkable robustness. Additionally, we examined the effects of minor disturbances on initial states that previously exhibited high overlap with scars and consistent revivals. Our analysis revealed that different types of disturbances can induce markedly different behaviors, such as partially "freezing" the chain, leading to sustained oscillations, or accelerating the process of thermalization.
Abstract We investigated the stability of quantum many-body scars under perturbations using a PXP model. Using numerical simulations, we analyzed the fidelity and correlation functions of the system to track its evolution and assess the persistence of revivals. We explored two distinct types of perturbations: imperfections in the initial state, which naturally arise in experimental settings, and disorder in the Hamiltonian, which was introduced as a computational tool to probe the system’s response to external disturbances. We found that while certain initial state modifications can partially stabilize oscillations by restricting the system’s accessible dynamics, others accelerate thermalization by increasing overlap with the full eigenstate spectrum. Similarly, disorder in the Hamiltonian gradually suppresses revivals and enhances thermalization, but scars demonstrate robustness for small perturbations. Our results provide insights into the conditions under which quantum many-body scars persist, offering valuable implications for experimental realizations and controlled quantum dynamics.