arXiv subjects

A. Ghirri

Publications and source records attributed to A. Ghirri.

5 recordsLinked to original sources

arXiv2025

Quantum sensing of time-dependent magnetic signals with molecular spins

Molecular spins offer a promising platform for quantum sensing, particularly in organic, supramolecular or biological environments. Recognition of the signals by these systems is of particular interest given their possible integration into more complex structures and their possible use as sensors in close proximity to analytes. In this work, we develop two quantum sensing protocols that enable discrimination between different time-dependent magnetic field, without requiring its periodicity to match with the microwave manipulating sequence. These are based on the Hahn echo sequence and have been tested on VO(TPP) and VOPt(SOCPh$)_{4}$ molecular spins embedded in a superconducting YBCO microwave planar resonator. We report a magnetic field sensitivity up to $2.57 \cdot 10^{-7} T Hz^{-\frac{1}{2}}$ (with lower bounds approaching $2.87 \cdot 10^{-8} T Hz^{-\frac{1}{2}})$ for signals with duration of a few microseconds. Under the given conditions, the minimum signal area that can be measured is in the $10^{-10}$ T s range, suggesting a potential trade-off between minimum measurable field and the required signal duration and memory time.

cond-mat.mes-hall↗

arXiv2016

Coherently coupling distinct spin ensembles through a high-$T_c$ superconducting resonator

The problem of coupling multiple spin ensembles through cavity photons is revisited by using PyBTM organic radicals and a high-$T_c$ superconducting coplanar resonator. An exceptionally strong coupling is obtained and up to three spin ensembles are simultaneously coupled. The ensembles are made physically distinguishable by chemically varying the $g$ factor and by exploiting the inhomogeneities of the applied magnetic field. The coherent mixing of the spin and field modes is demonstrated by the observed multiple anticrossing, along with the simulations performed within the input-output formalism, and quantified by suitable entropic measures.

cond-mat.mes-hall↗

arXiv2006

Tunable dipolar magnetism in high-spin molecular clusters

We report on the Fe17 high-spin molecular cluster and show that this system is an exemplification of nanostructured dipolar magnetism. Each Fe17 molecule, with spin S=35/2 and axial anisotropy as small as D=-0.02K, is the magnetic unit that can be chemically arranged in different packing crystals whilst preserving both spin ground-state and anisotropy. For every configuration, molecular spins are correlated only by dipolar interactions. The ensuing interplay between dipolar energy and anisotropy gives rise to macroscopic behaviors ranging from superparamagnetism to long-range magnetic order at temperatures below 1K.

cond-mat.mes-hall↗

arXiv2005

Molecular engineering of antiferromagnetic rings for quantum computation

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows to engineer its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S-mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.

cond-mat.mes-hall↗

arXiv2004

Topology and spin dynamics in magnetic molecules

We investigate the role of topology and distortions in the quantum dynamics of magnetic molecules, using a cyclic spin system as reference. We consider three variants of antiferromagnetic molecular ring, i.e. Cr$_8$, Cr$_7$Zn and Cr$_7$Ni, characterized by low lying states with different total spin $S$. We theoretically and experimentally study the low-temperature behavior of the magnetic torque as a function of the applied magnetic field. Near level crossings, this observable selectively probes quantum fluctuations of the total spin (''$S$ mixing") induced by lowering of the ideal ring symmetry. We show that while a typical distortion of a model molecular structure is very ineffective in opening new $S$-mixing channels, the spin topology is a major ingredient to control the degree of $S$ mixing. This conclusion is further substantiated by low-temperature heat capacity measurements.

cond-mat.mes-hall↗