Observation of many-body Fock space dynamics in two dimensions

Abstract

Quantum many-body simulation provides a straightforward way to understand fundamental physics and connect with quantum information applications. However, suffering from exponentially growing Hilbert space size, characterization in terms of few-body probes in real space is often insufficient to tackle challenging problems such as quantum critical behavior and many-body localization (MBL) in higher dimensions. Here, we experimentally employ a new paradigm on a superconducting quantum processor, exploring such elusive questions from a Fock space view: mapping the many-body system onto an unconventional Anderson model on a complex Fock space network of many-body states. By observing the wave packet propagating in Fock space and the emergence of a statistical ergodic ensemble, we reveal a fresh picture for characterizing representative manybody dynamics: thermalization, localization, and scarring. In addition, we observe a quantum critical regime of anomalously enhanced wave packet width and deduce a critical point from the maximum wave packet fluctuations, which lend support for the two-dimensional MBL transition in finite-sized systems. Our work unveils a new perspective of exploring many-body physics in Fock space, demonstrating its practical applications on contentious MBL aspects such as criticality and dimensionality. Moreover, the entire protocol is universal and scalable, paving the way to finally solve a broader range of controversial many-body problems on future larger quantum devices.

Enhanced quantum state transfer by circumventing quantum chaotic behavior

“…Its non-integrability renders quick thermalization and the absence of memory of the initial conditions throughout sufficiently long dynamics 36 . Therefore, the prospects of achieving a successful QST are slim: One expects diffusive behavior in Fock space 37 , making it unlikely to find a single state with the majority of the weight in at a later time. Yet, suppose the number of excitations is small compared to the total system size.…”

Disorder-tunable entanglement at infinite temperature

“…The latter entanglement structures have recently been identified ( 13 , 14 ) in a class of systems known as quantum many-body scars (QMBS) ( 15 – 17 ). When QMBS systems are prepared in special initial states, their dynamics become trapped in a subspace that does not mix with the thermalizing bulk of the spectrum, leading to the coherent time evolution of local observables ( 18 – 23 ). The observation of QMBS has triggered a flurry of theoretical efforts to understand and classify the general mechanisms of weak ergodicity breaking in isolated quantum systems ( 24 – 33 ).…”

Experimental Proposal on Non-Hermitian Skin Effect by Two-dimensional Quantum Walk with a Single Trapped Ion

“…Recent proposals extend such an implementation to study the quench dynamics of spin-orbit coupled systems and topological physics. [25,26] Recent theoretical and experimental works have extended quantum walks to higher-dimensions, [27] which is beneficial to investigations of special phenomena in non-Hermitian systems, such as the non-Hermitian skin effect (NHSE) in higher dimensions, [28][29][30][31] many-body Fock states with two dimensions, [32] and in the generation of GKP states. [33] In particular, directional matter transport has been experimentally demonstrated in a twodimensional (2D) quantum walk of photons, [34] which underlies the emergence of NHSE and has potential applications in topological transport and device design.…”