We provide two inequalities for estimating adiabatic fidelity in terms of two other more handily calculated quantities, i.e., generalized orthogonality catastrophe and quantum speed limit. As a... Show moreWe provide two inequalities for estimating adiabatic fidelity in terms of two other more handily calculated quantities, i.e., generalized orthogonality catastrophe and quantum speed limit. As a result of considering a two-dimensional subspace spanned by the initial ground state and its orthogonal complement, our method leads to stronger bounds on adiabatic fidelity than those previously obtained. One of the two inequalities is nearly sharp when the system size is large, as illustrated using a driven Rice-Mele model, which represents a broad class of quantum many-body systems whose overlap of different instantaneous ground states exhibits orthogonality catastrophe. Show less
Fermin, R.; Scheinowitz, N.M.A.; Aarts, J.; Lahabi, K. 2022
With the ever-increasing energy need to process big data, the realization of low-power computing technologies, such as superconducting logic and memories, has become a pressing issue. Developing... Show moreWith the ever-increasing energy need to process big data, the realization of low-power computing technologies, such as superconducting logic and memories, has become a pressing issue. Developing fast and nonvolatile superconducting memory elements, however, remains a challenge. Superconductor-ferromagnet hybrid devices offer a promising solution, as they combine ultrafast manipulation of spins with dissipationless readout. Here, we present a type of nonvolatile Josephson junction memory that utilizes the bistable magnetic texture of a single mesoscopic ferromagnet. We use micromagnetic simulations to design an ellipse-shaped planar junction structured from a Co/Nb bilayer. The ellipse can be prepared as uniformly magnetized or as a pair of vortices at zero applied field. The two states yield considerably different critical currents, enabling reliable electrical readout of the element. We describe the mechanism that controls the critical current by applying numerical calculations to quantify the local stray field from the ferromagnet, which shifts the superconducting interference pattern. Our approach presents a route towards realizing superconducting memory applications by combining micromagnetic modeling with bistable spin-textured junctions. Show less
We consider a family of tensor network states defined on regular lattices that come with a natural definition of an adiabatic path to prepare them. This family comprises relevant classes of states,... Show moreWe consider a family of tensor network states defined on regular lattices that come with a natural definition of an adiabatic path to prepare them. This family comprises relevant classes of states, such as injective matrix product and projected entangled-pair states, and some corresponding to classical spin models. We show how uniform lower bounds to the gap of the parent Hamiltonian along the adiabatic trajectory can be efficiently computed using semidefinite programming. This allows one to check whether the adiabatic preparation can be performed efficiently with a scalable effort. We also derive a set of observables whose expectation values can be easily determined and that form a complete set, in the sense that they uniquely characterize the state. We identify a subset of those observables which can be efficiently computed if one has access to the quantum state and local measurements, and analyze how they can be used in verification procedures. Show less
Koridon, E.; Yalouz, S.; Senjean, B.; Buda, F.; O’Brien, T. E.; Visscher, L. 2021
We introduce a new method to continuously map inhomogeneities of a moiré lattice and apply it to open-device twisted bilayer graphene (TBG). We show that the variation in the twist angle, which is... Show moreWe introduce a new method to continuously map inhomogeneities of a moiré lattice and apply it to open-device twisted bilayer graphene (TBG). We show that the variation in the twist angle, which is frequently conjectured to be the reason for differences between devices with a supposed similar twist angle, is about 0.04° over areas of several hundred nm, comparable to devices encapsulated between hBN slabs. We distinguish between an effective twist angle and local anisotropy and relate the latter to heterostrain. Our results suggest that the lack of evidence for superconductivity in open devices is not a consequence of higher heterogeneity in the twist angle, but possibly due to the absence of interaction with a top hBN layer. Furthermore, our results imply that for our devices, twist angle heterogeneity has a roughly equal effect to the electronic structure as local strain. The method introduced here is applicable to results from different imaging techniques, and on different moiré materials. Show less
Verweij R.W., Moerman P.G., Ligthart N.E.G., Huijnen L.P.P., Groenewold J., Kegel W.K., Blaaderen A. van, Kraft D.J. 2020
