1,721,018 research outputs found
Tafuri F, Stornaiuolo D, Lucignano P, Galletti L, Longobardi L, Massarotti D, Montemurro D, Papari G, Barone A, Tagliacozzo A
No full textHigh-accuracy Hamiltonian learning via delocalized quantum state evolutions
No full textLearning the unknown Hamiltonian governing the dynamics of a quantum many-body system is a challenging task. In this manuscript, we propose a possible strategy based on repeated measurements on a single time-dependent state. We prove that the accuracy of the learning process is maximized for states that are delocalized in the Hamiltonian eigenbasis. This implies that delocalization is a quantum resource for Hamiltonian learning, that can be exploited to select optimal initial states for learning algorithms. We investigate the error scaling of our reconstruction with respect to the number of measurements, and we provide examples of our learning algorithm on simulated quantum systems
Publisher's Note: Topological rf SQUID with a frustrating π junction for probing the Majorana bound state
No full textEditorial: innovative quantum materials
No full textQuantum Materials are materials where the manifestation of the quantum mechanical nature of matter constituents, which comes into evidence at the macroscopic scale, is used to obtain new functionalities. The study of quantum materials is relevant both on the fundamental and on the applied side. Indeed, this class of materials provides a common thread between physics, materials science and engineering. The focus is on emergent excitations, such as Dirac and Majorana fermions. In particular, it analyzes their sensitivity to external perturbations, such as electric and magnetic fields, and boundary conditions that can be controlled by surface/edge terminations, defect states and nanostructuring. The topical issue provides a broad description of innovative quantum materials discussing a variety of different phenomena: (1) interference phenomena in quantum devices made up of a topological insulator, (2) bound states in finite length nanowires with an inhomogeneous spin–orbit coupling profile relevant for Majorana physics, (3) sensitivity of graphene transport properties to defect states and edge functionalization, (4) role of Moiré phonons on the energy properties of twisted bilayer graphene at the magic angle important for van der Waals materials, (5) emergent spin excitations and anisotropic magnetotransport properties in iridates, (6) magnetoelectric couplings and improper magnetoelectric behavior in manganites significant for the realization of novel spintronic devices
Optimal quantum annealing: A variational shortcut-to-adiabaticity approach
No full textSuppressing unwanted transitions out of the instantaneous ground state is a major challenge in unitary adiabatic quantum computation. A recent approach consists in building counterdiabatic potentials approximated using variational strategies. In this contribution, we extend this variational approach to Lindbladian dynamics, having as a goal the suppression of diabatic transitions between pairs of Jordan blocks in quantum annealing. We show that, surprisingly, unitary counterdiabatic Ansätze are successful for dissipative dynamics as well, allowing for easier experimental implementations compared to Lindbladian Ansätze involving dissipation. Our approach not only guarantees improvements of open-system adiabaticity but also enhances the success probability of quantum annealing
Realization of 0- π states in superconductor/ferromagnetic insulator/superconductor Josephson junctions: The role of spin-orbit interaction and lattice impurities
No full textJosephson devices with ferromagnetic barriers have been widely studied. Much less is known when the ferromagnetic layer is insulating. In this paper we investigate the transport properties of superconductor/ferromagnetic insulator/superconductor (SFIS) junctions with particular attention paid to the temperature behavior of the critical current that may be used as a fingerprint of the junction. We investigate the specific role of impurities as well as of possible spin-mixing mechanisms due to the spin-orbit coupling. The transition between the 0 and the π phases can be properly tuned, thus achieving stable π junctions over the entire temperature range that may be possibly employed in superconducting quantum circuits
Two-level physics in a model metallic break junction
No full textWe consider a model inspired by a metal break junction hypothetically
caught at its breaking point, where the nonadiabatic center-of-mass
motion of the bridging atom can be treated as a two-level system. By
means of numerical renormalization group (NRG) we calculate the
influence of the two-level system on the ballistic conductance across
the bridge atom. The results are shown to be fully consistent with a
conformal field theory treatment. We find that the conductance
calculated by coupling Fermi-liquid theory to our NRG is always finite
and fractional at zero temperature but drops quite fast as the
temperature increases
High critical temperature nodal superconductors as building block for time-reversal invariant topological superconductivity
Full text linkDestruction of Kondo correlations in a four electron quantum dot with Spin-Orbit interactions
No full textPhysica E: Low-dimensional Systems and Nanostructures, 42 (4),
p.860-86
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