Search results for "Quàntums"
showing 9 items of 9 documents
Vibronic Model for Intercommunication of Localized Spins via Itinerant Electron
2019
In this article, we propose a vibronic pseudo Jahn–Teller model for partially delocalized mixed-valence molecules aimed to describe the magnetic coupling between the localized spins mediated by the delocalized electron. The simplest partially delocalized system that retains the main studied features is assumed to consist of a one-electron mixed-valence dimer, which is connected to the two terminal magnetic ions. The model involves the following key interactions: electron transfer in the spin-delocalized subsystem of a mixed-valence molecule, which is mimicked by a dimeric unit, coupling of the itinerant electrons with the molecular vibrations, and isotropic magnetic exchange between the loc…
Molecular spins for quantum computation
2019
Spins in solids or in molecules possess discrete energy levels, and the associated quantum states can be tuned and coherently manipulated by means of external electromagnetic fields. Spins therefore provide one of the simplest platforms to encode a quantum bit (qubit), the elementary unit of future quantum computers. Performing any useful computation demands much more than realizing a robust qubit—one also needs a large number of qubits and a reliable manner with which to integrate them into a complex circuitry that can store and process information and implement quantum algorithms. This ‘scalability’ is arguably one of the challenges for which a chemistry-based bottom-up approach is best-s…
Quantum Phases and Spin Liquid Properties of 1T-TaS2
2021
Quantum materials exhibiting magnetic frustration are connected to diverse phenomena including high-Tc superconductivity, topological order and quantum spin liquids (QSLs). A QSL is a quantum phase (QP) related to a quantum-entangled fluid-like state of matter. Previous experiments on QSL candidate materials are usually interpreted in terms of a single QP, although theories indicate that many distinct QPs are closely competing in typical frustrated spin models. Here we report on combined temperature-dependent muon spin relaxation and specific heat measurements for the triangular-lattice QSL candidate material 1T-TaS2 that provide evidence for competing QPs. The measured properties are assig…
Black hole radiance, short distances and TeV gravity.
2006
Using a derivation of black hole radiance in terms of two-point functions one can provide a quantitative estimate of the contribution of short distances to the spectrum. Thermality is preserved for black holes with $��l_P <<1$. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.
An effective field theory approach to the QCD corrections to the large-mt Zbb vertex
1995
Using effective field theory techniques we discuss the QCD corrections to the large-mt contributions to the process Z → bb. In particular we obtain the αs correction to the non-universal log mt contribution to the Zbb vertex.
Ground-state spin blockade in a single-molecule junction
2019
It is known that the quantum mechanical ground state of a nanoscale junction has a significant impact on its electrical transport properties. This becomes particularly important in transistors consisting of a single molecule. Because of strong electron-electron interactions and the possibility of accessing ground states with high spins, these systems are eligible hosts of a current-blockade phenomenon called a ground-state spin blockade. This effect arises from the inability of a charge carrier to account for the spin difference required to enter the junction, as that process would violate the spin selection rules. Here, we present a direct experimental demonstration of a ground-state spin …
Decoherence from dipolar interspin interactions in molecular spin qubits
2019
The realization of spin-based logical gates crucially depends on magnetically coupled spin qubits. Thus, understanding decoherence when spin qubits are in close proximity will become a roadblock to overcome. Herein, we propose a method free of fitting parameters to evaluate the qubit phase memory time ${T}_{m}$ in samples with high electron spin concentrations. The method is based on a model aimed to estimate magnetic nuclear decoherence [P. C. E. Stamp and I. S. Tupitsyn, Phys. Rev. B 69, 014401 (2004)]. It is applied to a ground-spin $J=8$ magnetic molecule 1 displaying atomic clock transitions, namely ${{[\mathrm{H}{\mathrm{o}}^{\mathrm{III}}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9…
Exploiting Clock Transitions for the chemical design of resilient molecular spin qubits
2021
Molecular spin qubits are chemical nanoobjects with promising applications that are so far hampered by the rapid loss of quantum information, a process known as decoherence. A strategy to improve this situation involves employing so-called Clock Transitions (CTs), which arise at anticrossings between spin energy levels. At CTs, the spin states are protected from magnetic noise and present an enhanced quantum coherence. Unfortunately, these optimal points are intrinsically hard to control since their transition energy cannot be tuned by an external magnetic field; moreover, their resilience towards geometric distortions has not yet been analyzed. Here we employ a python-based computational t…
Quantum coherent spin-electric control in a molecular nanomagnet at clock transitions
2020
Electrical control of spins at the nanoscale offers significant architectural advantages in spintronics, because electric fields can be confined over shorter length scales than magnetic fields1–5. Thus, recent demonstrations of electric-field sensitivities in molecular spin materials6–8 are tantalizing, raising the viability of the quantum analogues of macroscopic magneto-electric devices9–15. However, the electric-field sensitivities reported so far are rather weak, prompting the question of how to design molecules with stronger spin–electric couplings. Here we show that one path is to identify an energy scale in the spin spectrum that is associated with a structural degree of freedom with…