Magnetic edge states and coherent manipulation of graphene nanoribbons.

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths2,3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons5,6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.

Publisher Correction: Magnetic edge states and coherent manipulation of graphene nanoribbons.

In Fig. 1 of this Letter, there should have been two nitrogen (N) atoms at the 1,3-positions of all the blue chemical structures (next to the oxygen atoms), rather than one at the 2-position. The figure has been corrected online, and the original incorrect figure is shown as Supplementary Information to the accompanying Amendment.

Inherent Spin-Polarization Coupling in a Magnetoelectric Vortex.

Solid-state materials are currently being explored as a platform for the manipulation of spins for spintronics and quantum information science. More broadly, a wide spectrum of ferroelectric materials, spanning from inorganic oxides to polymeric systems such as PVDF, present a different approach to explore quantum phenomena in which the spins are set and manipulated with electric fields. Using dilute Fe3+-doped ferroelectric PbTiO3-SrTiO3 superlattices as a model system, we demonstrate intrinsic spin-polarization control of spin directionality in complex ferroelectric vortices and skyrmions. Electron paramagnetic resonance (EPR) spectra show that the spins in the Fe3+ ion are strongly coupled to the local polarization and preferentially aligned perpendicular to the ferroelectric polar c axis in this complex vortex structure. The effect of polarization-spin directionality is corroborated by first-principles calculations, demonstrating the variation of the spin directionality with the polar texture and offering the potential for future quantum analogues of macroscopic magnetoelectric devices.

A national service for delivering CD19 CAR-Tin large B-cell lymphoma - The UK real-world experience.

CD19 CAR-T have emerged as a new standard treatment for relapsed/refractory (r/r) large B-cell lymphoma (LBCL). CAR-T real-world (RW) outcomes published to date suggest significant variability across countries. We provide results of a large national cohort of patients intended to be treated with CAR-T in the UK. Consecutive patients with r/r LBCL approved for CAR-T by the National CAR-T Clinical Panel between December 2018 and November 2020 across all UK CAR-T centres were included. 404/432 patients were approved [292 axicabtagene ciloleucel (axi-cel), 112 tisagenlecleucel (tisa-cel)], 300 (74%) received the cells. 110/300 (38.3%) patients achieved complete remission (CR) at 6 months (m). The overall response rate was 77% (52% CR) for axi-cel, 57% (44% CR) for tisa-cel. The 12-month progression-free survival was 41.8% (axi-cel) and 27.4% (tisa-cel). Median overall survival for the intention-to-treat population was 10.5 m, 16.2 m for infused patients. The incidence of grade ≥3 cytokine release syndrome and neurotoxicity were 7.6%/19.6% for axi-cel and 7.9%/3.9% for tisa-cel. This prospective RW population of CAR-T eligible patients offers important insights into the clinical benefit of CD19 CAR-T in LBCL in daily practice. Our results confirm long-term efficacy in patients receiving treatment similar to the pivotal trials, but highlight the significance of early CAR-T failure.

Electric Field Control of Spins in Molecular Magnets.

Coherent control of individual molecular spins in nanodevices is a pivotal prerequisite for fulfilling the potential promised by molecular spintronics. By applying electric field pulses during time-resolved electron spin resonance measurements, we measure the sensitivity of the spin in several antiferromagnetic molecular nanomagnets to external electric fields. We find a linear electric field dependence of the spin states in Cr_{7}Mn, an antiferromagnetic ring with a ground-state spin of S=1, and in a frustrated Cu_{3} triangle, both with coefficients of about 2 rad s^{-1}/V m^{-1}. Conversely, the antiferromagnetic ring Cr_{7}Ni, isomorphic with Cr_{7}Mn but with S=1/2, does not exhibit a detectable effect. We propose that the spin-electric field coupling may be used for selectively controlling individual molecules embedded in nanodevices.

Endohedral Metallofullerene as Molecular High Spin Qubit: Diverse Rabi Cycles in Gd2@C79N.

An anisotropic high-spin qubit with long coherence time could scale the quantum system up. It has been proposed that Grover's algorithm can be implemented in such systems. Dimetallic aza[80]fullerenes M2@C79N (M = Y or Gd) possess an unpaired electron located between two metal ions, offering an opportunity to manipulate spin(s) protected in the cage for quantum information processing. Herein, we report the crystallographic determination of Gd2@C79N for the first time. This molecular magnet with a collective high-spin ground state (S = 15/2) generated by strong magnetic coupling (JGd-Rad = 350 ± 20 cm-1) has been unambiguously validated by magnetic susceptibility experiments. Gd2@C79N has quantum coherence and diverse Rabi cycles, allowing arbitrary superposition state manipulation between each adjacent level. The phase memory time reaches 5 µs at 5 K by dynamic decoupling. This molecule fulfills the requirements of Grover's searching algorithm proposed by Leuenberger and Loss.

Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet.

Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.

Quantum Interference in Graphene Nanoconstrictions.

We report quantum interference effects in the electrical conductance of chemical vapor deposited graphene nanoconstrictions fabricated using feedback controlled electroburning. The observed multimode Fabry-Pérot interferences can be attributed to reflections at potential steps inside the channel. Sharp antiresonance features with a Fano line shape are observed. Theoretical modeling reveals that these Fano resonances are due to localized states inside the constriction, which couple to the delocalized states that also give rise to the Fabry-Pérot interference patterns. This study provides new insight into the interplay between two fundamental forms of quantum interference in graphene nanoconstrictions.

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine).

The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]EF6 (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero-field splitting (ZFS) being observed. The magnetism of 1-4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J⊥) being slightly stronger than the intralayer interaction along Ni-pyz-Ni segments (J(pyz)) within the two-dimensional [Ni(pyz)2](2+) square planes. Regardless of X, J(pyz) is similar for the four compounds and is roughly 1 K.

A spin-frustrated trinuclear copper complex based on triaminoguanidine with an energetically well-separated degenerate ground state.

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

All-Electrical Driving and Probing of Dressed States in a Single Spin.

The subnanometer distance between tip and sample in a scanning tunneling microscope (STM) enables the application of very large electric fields with a strength as high as ∼1 GV/m. This has allowed for efficient electrical driving of Rabi oscillations of a single spin on a surface at a moderate radiofrequency (RF) voltage on the order of tens of millivolts. Here, we demonstrate the creation of dressed states of a single electron spin localized in the STM tunnel junction by using resonant RF driving voltages. The read-out of these dressed states was achieved all electrically by a weakly coupled probe spin. Our work highlights the strength of the atomic-scale geometry inherent to the STM that facilitates the creation and control of dressed states, which are promising for the design of atomic scale quantum devices using individual spins on surfaces.

A continuous-wave and pulsed X-band electron spin resonance spectrometer operating in ultra-high vacuum for the study of low dimensional spin ensembles.

We report the development of a continuous-wave and pulsed X-band electron spin resonance (ESR) spectrometer for the study of spins on ordered surfaces down to cryogenic temperatures. The spectrometer operates in ultra-high vacuum and utilizes a half-wavelength microstrip line resonator realized using epitaxially grown copper films on single crystal Al2O3 substrates. The one-dimensional microstrip line resonator exhibits a quality factor of more than 200 at room temperature, close to the upper limit determined by radiation losses. The surface characterizations of the copper strip of the resonator by atomic force microscopy, low-energy electron diffraction, and scanning tunneling microscopy show that the surface is atomically clean, flat, and single crystalline. Measuring the ESR spectrum at 15 K from a few nm thick molecular film of YPc2, we find a continuous-wave ESR sensitivity of 2.6 × 1011 spins/G · Hz1/2, indicating that a signal-to-noise ratio of 3.9 G · Hz1/2 is expected from a monolayer of YPc2 molecules. Advanced pulsed ESR experimental capabilities, including dynamical decoupling and electron-nuclear double resonance, are demonstrated using free radicals diluted in a glassy matrix.

Coherent spin control by electrical manipulation of the magnetic anisotropy.

High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple, almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields.

Fluctuating superconductivity in organic molecular metals close to the Mott transition.

On cooling through the transition temperature T(c) of a conventional superconductor, an energy gap develops as the normal-state charge carriers form Cooper pairs; these pairs form a phase-coherent condensate that exhibits the well-known signatures of superconductivity: zero resistivity and the expulsion of magnetic flux (the Meissner effect). However, in many unconventional superconductors, the formation of the energy gap is not coincident with the formation of the phase-coherent superfluid. Instead, at temperatures above the critical temperature a range of unusual properties, collectively known as 'pseudogap phenomena', are observed. Here we argue that a key pseudogap phenomenon-fluctuating superconductivity occurring substantially above the transition temperature-could be induced by the proximity of a Mott-insulating state. The Mott-insulating state in the kappa-(BEDT-TTF)2X organic molecular metals can be tuned, without doping, through superconductivity into a normal metallic state as a function of the parameter t/U, where t is the tight-binding transfer integral characterizing the metallic bandwidth and U is the on-site Coulomb repulsion. By exploiting a particularly sensitive probe of superconducting fluctuations, the vortex-Nernst effect, we find that a fluctuating regime develops as t/U decreases and the role of Coulomb correlations increases.

Title: experimental realisation of multi-qubit gates using electron paramagnetic resonance.

Quantum information processing promises to revolutionise computing; quantum algorithms have been discovered that address common tasks significantly more efficiently than their classical counterparts. For a physical system to be a viable quantum computer it must be possible to initialise its quantum state, to realise a set of universal quantum logic gates, including at least one multi-qubit gate, and to make measurements of qubit states. Molecular Electron Spin Qubits (MESQs) have been proposed to fulfil these criteria, as their bottom-up synthesis should facilitate tuning properties as desired and the reproducible production of multi-MESQ structures. Here we explore how to perform a two-qubit entangling gate on a multi-MESQ system, and how to readout the state via quantum state tomography. We propose methods of accomplishing both procedures using multifrequency pulse Electron Paramagnetic Resonance (EPR) and apply them to a model MESQ structure consisting of two nitroxide spin centres. Our results confirm the methodological principles and shed light on the experimental hurdles which must be overcome to realise a demonstration of controlled entanglement on this system.

Probing the Local Electronic Structure in Metal Halide Perovskites through Cobalt Substitution.

Owing to the unique chemical and electronic properties arising from 3d-electrons, substitution with transition metal ions is one of the key routes for engineering new functionalities into materials. While this approach has been used extensively in complex metal oxide perovskites, metal halide perovskites have largely resisted facile isovalent substitution. In this work, it is demonstrated that the substitution of Co2+ into the lattice of methylammonium lead triiodide imparts magnetic behavior to the material while maintaining photovoltaic performance at low concentrations. In addition to comprehensively characterizing its magnetic properties, the Co2+ ions themselves are utilized as probes to sense the local electronic environment of Pb in the perovskite, thereby revealing the nature of their incorporation into the material. A comprehensive understanding of the effect of transition metal incorporation is provided, thereby opening the substitution gateway for developing novel functional perovskite materials and devices for future technologies.

Coherent state transfer between an electron and nuclear spin in (15)N@C(60).

Electron spin qubits in molecular systems offer high reproducibility and the ability to self-assemble into larger architectures. However, interactions between neighboring qubits are "always on," and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both effectively turn on or off interqubit coupling mediated by dipolar interactions and benefit from the long nuclear spin decoherence times (T(2n)). We transfer qubit states between the electron and (15)N nuclear spin in (15)N@C(60) with a two-way process fidelity of 88%, using a series of tuned microwave and radio frequency pulses and measure a nuclear spin coherence lifetime of over 100 ms.

Coherent electric field manipulation of Fe3+ spins in PbTiO3.

Magnetoelectrics, materials that exhibit coupling between magnetic and electric degrees of freedom, not only offer a rich environment for studying the fundamental materials physics of spin-charge coupling but also present opportunities for future information technology paradigms. We present results of electric field manipulation of spins in a ferroelectric medium using dilute ferric ion-doped lead titanate as a model system. Combining first-principles calculations and electron paramagnetic resonance (EPR), we show that the ferric ion spins are preferentially aligned perpendicular to the ferroelectric polar axis, which we can manipulate using an electric field. We also demonstrate coherent control of the phase of spin superpositions by applying electric field pulses during time-resolved EPR measurements. Our results suggest a new pathway toward the manipulation of spins for quantum and classical spintronics.

Probing resonating valence bond states in artificial quantum magnets.

Designing and characterizing the many-body behaviors of quantum materials represents a prominent challenge for understanding strongly correlated physics and quantum information processing. We constructed artificial quantum magnets on a surface by using spin-1/2 atoms in a scanning tunneling microscope (STM). These coupled spins feature strong quantum fluctuations due to antiferromagnetic exchange interactions between neighboring atoms. To characterize the resulting collective magnetic states and their energy levels, we performed electron spin resonance on individual atoms within each quantum magnet. This gives atomic-scale access to properties of the exotic quantum many-body states, such as a finite-size realization of a resonating valence bond state. The tunable atomic-scale magnetic field from the STM tip allows us to further characterize and engineer the quantum states. These results open a new avenue to designing and exploring quantum magnets at the atomic scale for applications in spintronics and quantum simulations.