Molecular nanomagnets: a viable path toward quantum information processing?

Molecular nanomagnets (MNMs), molecules containing interacting spins, have been a playground for quantum mechanics. They are characterized by many accessible low-energy levels that can be exploited to store and process quantum information. This naturally opens the possibility of using them as qudits, thus enlarging the tools of quantum logic with respect to qubit-based architectures. These additional degrees of freedom recently prompted the proposal for encoding qubits with embedded quantum error correction (QEC) in single molecules. QEC is the holy grail of quantum computing and this qudit approach could circumvent the large overhead of physical qubits typical of standard multi-qubit codes. Another important strength of the molecular approach is the extremely high degree of control achieved in preparing complex supramolecular structures where individual qudits are linked preserving their individual properties and coherence. This is particularly relevant for building quantum simulators, controllable systems able to mimic the dynamics of other quantum objects. The use of MNMs for quantum information processing is a rapidly evolving field which still requires to be fully experimentally explored. The key issues to be settled are related to scaling up the number of qudits/qubits and their individual addressing. Several promising possibilities are being intensively explored, ranging from the use of single-molecule transistors or superconducting devices to optical readout techniques. Moreover, new tools from chemistry could be also at hand, like the chiral-induced spin selectivity. In this paper, we will review the present status of this interdisciplinary research field, discuss the open challenges and envisioned solution paths which could finally unleash the very large potential of molecular spins for quantum technologies.

Erratum: Many-Body Models for Molecular Nanomagnets [Phys. Rev. Lett. 110, 157204 (2013)].

This corrects the article DOI: 10.1103/PhysRevLett.110.157204.

Magnetic Exchange Interactions in the Molecular Nanomagnet Mn_{12}.

The discovery of magnetic bistability in Mn_{12} more than 20 years ago marked the birth of molecular magnetism, an extremely fertile interdisciplinary field and a powerful route to create tailored magnetic nanostructures. However, the difficulty to determine interactions in complex polycentric molecules often prevents their understanding. Mn_{12} is an outstanding example of this difficulty: although it is the forefather and most studied of all molecular nanomagnets, an unambiguous determination of even the leading magnetic exchange interactions is still lacking. Here we exploit four-dimensional inelastic neutron scattering to portray how individual spins fluctuate around the magnetic ground state, thus fixing the exchange couplings of Mn_{12} for the first time. Our results demonstrate the power of four-dimensional inelastic neutron scattering as an unrivaled tool to characterize magnetic clusters.

Association of metabolic syndrome with kidney function and histology in living kidney donors.

The selection of living kidney donors is based on a formal evaluation of the state of health. However, this spectrum of health includes subtle metabolic derangements that can cluster as metabolic syndrome. We studied the association of metabolic syndrome with kidney function and histology in 410 donors from 2005 to 2012, of whom 178 donors were systematically followed after donation since 2009. Metabolic syndrome was defined as per the NCEP ATPIII criteria, but using a BMI > 25 kg/m(2) instead of waist circumference. Following donation, donors received counseling on lifestyle modification. Metabolic syndrome was present in 50 (12.2%) donors. Donors with metabolic syndrome were more likely to have chronic histological changes on implant biopsies than donors with no metabolic syndrome (29.0% vs. 9.3%, p < 0.001). This finding was associated with impaired kidney function recovery following donation. At last follow-up, reversal of metabolic syndrome was observed in 57.1% of donors with predonation metabolic syndrome, while only 10.8% of donors developed de novo metabolic syndrome (p < 0.001). In conclusion, metabolic syndrome in donors is associated with chronic histological changes, and nephrectomy in these donors was associated with subsequent protracted recovery of kidney function. Importantly, weight loss led to improvement of most abnormalities that define metabolic syndrome.

Quantum information processing with hybrid spin-photon qubit encoding.

We introduce a scheme to perform quantum information processing that is based on a hybrid spin-photon qubit encoding. The proposed qubits consist of spin ensembles coherently coupled to microwave photons in coplanar waveguide resonators. The quantum gates are performed solely by shifting the resonance frequencies of the resonators on a nanosecond time scale. An additional cavity containing a Cooper-pair box is exploited as an auxiliary degree of freedom to implement two-qubit gates. The generality of the scheme allows its potential implementation with a wide class of spin systems.

Many-body models for molecular nanomagnets.

We present a flexible and effective ab initio scheme to build many-body models for molecular nanomagnets, and to calculate magnetic exchange couplings and zero-field splittings. It is based on using localized Foster-Boys orbitals as a one-electron basis. We apply this scheme to three paradigmatic systems, the antiferromagnetic rings Cr8 and Cr7Ni, and the single-molecule magnet Fe4. In all cases we identify the essential magnetic interactions and find excellent agreement with experiments.

Theoretical Design of Optimal Molecular Qudits for Quantum Error Correction.

We pinpoint the key ingredients ruling decoherence in multispin clusters, and we engineer the system Hamiltonian to design optimal molecules embedding quantum error correction. These are antiferromagnetically coupled systems with competing exchange interactions, characterized by many low-energy states in which decoherence is dramatically suppressed and does not increase with the system size. This feature allows us to derive optimized code words, enhancing the power of the quantum error correction code by orders of magnitude. We demonstrate this by a complete simulation of the system dynamics, including the effect of decoherence driven by a nuclear spin bath and the full sequence of pulses to implement error correction and logical gates between protected states.

Burden of phenylketonuria in Latin American patients: a systematic review and meta-analysis of observational studies.

BACKGROUND: Phenylketonuria (PKU) is an inborn error of metabolism caused by a deficiency of the enzyme phenylalanine hydroxylase. If untreated, the complications of PKU lead to significant neucognitive and neuropsychiatric impairments, placing a burden on both the individual's quality of life and on the healthcare system. We conducted a systematic literature review to characterize the impact of PKU on affected individuals and on healthcare resources in Latin American (LATAM) countries. METHODS: Searches of the global medical literature as well as regional and local medical literature up to September 2021. Observational studies on patients with PKU from any LATAM country. Pairs of reviewers independently screened eligible articles, extracted data from included studies, and assessed their risk of bias. RESULTS: 79 unique studies (47 cross-sectional studies, 18 case series, 12 case reports, and two cohort studies) with a total of 4090 patients were eligible. Of these studies, 20 had data available evaluating early-diagnosed PKU patients for meta-analysis of burden outcomes. Intellectual disability in the pooled studies was 18% [95% Confidence Interval (CI) 0.04-0.38; I2 = 83.7%, p = 0.0133; two studies; n = 114]. Motor delay was 15% [95% CI 0.04-0.30; I2 = 74.5%, p = 0.0083; four studies; n = 132]. Speech deficit was 35% [95% CI 0.08-0.68; I2 = 93.9%, p < 0.0001; five studies; n = 162]. CONCLUSIONS: There is currently evidence of high clinical burden in PKU patients in LATAM countries. Recognition that there are many unmet neuropsychological needs and socioeconomic challenges faced in the LATAM countries is the first step in planning cost-effective interventions.

Virologic and immunologic monitoring of cytomegalovirus to guide preemptive therapy in solid-organ transplantation.

Control of human cytomegalovirus (HCMV) infection during the posttransplant period was investigated in 134 solid-organ transplant recipients by monitoring in parallel virologic and immunologic parameters for at least 1 year of follow-up. Virologic monitoring was achieved by determining HCMV DNAemia with real-time PCR, using the threshold of 300 000 DNA copies/mL blood as a cutoff for starting preemptive therapy. Immunologic monitoring included measurement of HCMV-specific CD4+ and CD8+ T cells by cytokine flow cytometry, using HCMV-infected dendritic cells as a stimulus. HCMV infection was diagnosed in 110 (82%) and required treatment in 49 (36%) patients. At 12 months after transplantation 'protective' immunity (≥0.4 CD4+ and CD8+ HCMV-specific T cells/µL blood) was achieved in 115/129 (89%) patients. During the entire study period, 122 patients reconstituting HCMV-specific CD4+ and CD8+ T-cell immunity at 60 days posttransplant onward were able to control HCMV infection, except for one patient who developed HCMV disease because of a rejection episode. Patients reconstituting HCMV-specific CD8+ only did not control HCMV infection. In conclusion, the presence of both HCMV-specific CD4+ and CD8+ T cells ≥ 0.4/µL blood appears to be protective against HCMV disease. This result does not apply to patients undergoing antirejection treatment, or reconstituting HCMV-specific CD8+ T cells only.

Early onset of primary hypogonadism revealed by serum anti-Müllerian hormone determination during infancy and childhood in trisomy 21.

Male patients with an extra sex chromosome or autosome are expected to present primary hypogonadism at puberty owing to meiotic germ-cell failure. Scarce information is available on trisomy 21, a frequent autosomal aneuploidy. Our objective was to assess whether trisomy 21 presents with pubertal-onset, germ-cell specific, primary hypogonadism in males, or whether the hypogonadism is established earlier and affects other testicular cell populations. We assessed the functional status of the pituitary-testicular axis, especially Sertoli cell function, in 117 boys with trisomy 21 (ages: 2months-20year). To compare with an adequate control population, we established reference levels for serum anti-Müllerian hormone (AMH) in 421 normal males, from birth to adulthood, using a recently developed ultrasensitive assay. In trisomy 21, AMH was lower than normal, indicating Sertoli cell dysfunction, from early infancy, independently of the existence of cryptorchidism. The overall prevalence rate of AMH below the 3rd percentile was 64.3% in infants with trisomy 21. Follicle-stimulating hormone was elevated in patients <6months and after pubertal onset. Testosterone was within the normal range, but luteinizing hormone was elevated in most patients <6months and after pubertal onset, indicating a mild Leydig cell dysfunction. We conclude that in trisomy 21, primary hypogonadism involves a combined dysfunction of Sertoli and Leydig cells, which can be observed independently of cryptorchidism soon after birth, thus prompting the search for new hypotheses to explain the pathophysiology of gonadal dysfunction in autosomal trisomy.

Assessing the Nature of Chiral-Induced Spin Selectivity by Magnetic Resonance.

Understanding chiral-induced spin selectivity (CISS), resulting from charge transport through helical systems, has recently inspired many experimental and theoretical efforts but is still the object of intense debate. In order to assess the nature of CISS, we propose to focus on electron-transfer processes occurring at the single-molecule level. We design simple magnetic resonance experiments, exploiting a qubit as a highly sensitive and coherent magnetic sensor, to provide clear signatures of the acceptor polarization. Moreover, we show that information could even be obtained from time-resolved electron paramagnetic resonance experiments on a randomly oriented solution of molecules. The proposed experiments will unveil the role of chiral linkers in electron transfer and could also be exploited for quantum computing applications.

A systematic review of neurobiological and clinical features of mindfulness meditations.

BACKGROUND: Mindfulness meditation (MM) practices constitute an important group of meditative practices that have received growing attention. The aim of the present paper was to systematically review current evidence on the neurobiological changes and clinical benefits related to MM practice in psychiatric disorders, in physical illnesses and in healthy subjects. METHOD: A literature search was undertaken using Medline, ISI Web of Knowledge, the Cochrane collaboration database and references of retrieved articles. Controlled and cross-sectional studies with controls published in English up to November 2008 were included. RESULTS: Electroencephalographic (EEG) studies have revealed a significant increase in alpha and theta activity during meditation. Neuroimaging studies showed that MM practice activates the prefrontal cortex (PFC) and the anterior cingulate cortex (ACC) and that long-term meditation practice is associated with an enhancement of cerebral areas related to attention. From a clinical viewpoint, Mindfulness-Based Stress Reduction (MBSR) has shown efficacy for many psychiatric and physical conditions and also for healthy subjects, Mindfulness-Based Cognitive Therapy (MBCT) is mainly efficacious in reducing relapses of depression in patients with three or more episodes, Zen meditation significantly reduces blood pressure and Vipassana meditation shows efficacy in reducing alcohol and substance abuse in prisoners. However, given the low-quality designs of current studies it is difficult to establish whether clinical outcomes are due to specific or non-specific effects of MM. DISCUSSION: Despite encouraging findings, several limitations affect current studies. Suggestions are given for future research based on better designed methodology and for future directions of investigation.

Molecular Nanomagnets as Qubits with Embedded Quantum-Error Correction.

We show that molecular nanomagnets have a potential advantage in the crucial rush toward quantum computers. Indeed, the sizable number of accessible low-energy states of these systems can be exploited to define qubits with embedded quantum error correction. We derive the scheme to achieve this crucial objective and the corresponding sequence of microwave/radiofrequency pulses needed for the error correction procedure. The effectiveness of our approach is shown already with a minimal S = 3/2 unit corresponding to an existing molecule, and the scaling to larger spin systems is quantitatively analyzed.

Use of a D-optimal mixture design to estimate the effects of diverse chloride salts on the growth parameters of Lactobacillus pentosus.

The effects of NaCl, KCl, CaCl(2), and MgCl(2) and their mixtures on the ionic strength (IS) of the medium and the growth parameters of Lactobacillus pentosus were studied by means of a D-optimal mixture experimental design with constrains (total salt concentrationCaCl(2)>NaCl>KCl. Within the experimental region, the lag phase duration (lambda) was mainly affected by NaCl and CaCl(2) and the interaction KCl with MgCl(2). The maximum specific growth rate (mu(max)) decreased as NaCl (the highest effect), CaCl(2), and MgCl(2) increased (regardless of the presence or not of previous NaCl); low KCl concentrations had a stimulating effect on mu(max), but its overall effect showed a similar trend to the other salts. The maximum population reached (N(max)) was the least affected parameter and decreased as NaCl and CaCl(2) concentrations increased regardless of the presence of the other salts. The equations that expressed the growth parameters as a function of the diverse chloride salts, within the limits assayed, were developed and the corresponding z- and harmonic Z-values were estimated.

Impact of resection margin status on oncological outcomes after CO2 laser cordectomy.

The management of positive resection margins in micro-endoscopic glottic laser surgery remains a controversial and critical point. This study aims to assess the impact of margin status after transoral laser surgery on local control, survival and organ preservation rates; the decision-making process and treatment options in cases with positive margins are also discussed. We retrospectively reviewed the clinical and histological records of 308 consecutive patients with primary early glottic carcinoma (T1a, T1b, selected T2) and treated with endoscopic laser cordectomy. Recurrence rates and survival related to margin status were analysed using the Kaplan-Meier method. Local relapses and disease-free-survival rates were significantly related to excision margin status (p < 0.001). In the T1a category (n = 228) no significant differences were observed in disease-free-survival (p = 0.889) and overall survival (p = 0.426) between patients submitted to further treatment (revision endoscopic surgery or radiotherapy) for positive excision margins and patients who were left untreated. In 20 of 24 (83%) patients with positive margins that were surgically re-excised, no residual carcinoma was detected. Margin status (mainly multifocal and deep positive margins) at first surgery was significantly related to the final organ preservation rate (p < 0.001). Margin status during laser cordectomy in early glottic cancer has a prognostic impact on local control of disease without compromising survival. Patients with multifocal and deep positive borders should be surgically retreated and strictly monitored to increase the organ preservation rates. Careful preparation and mapping of the surgical specimen enhances the accuracy of pathological examination by reducing the risk of overestimate positive margins.

Control of human cytomegalovirus infection in patients infected with human immunodeficiency virus by high levels of specific CD8+ T-cells.

A new technique was used to simultaneously determine human cytomegalovirus (HCMV)-specific CD4(+) and CD8(+) T-cells in highly active anti-retroviral therapy (HAART)-naive and HAART-treated patients infected with human immunodeficiency virus (HIV). HIV-infected patients with HCMV infection, but without HCMV disease, showed low numbers of HCMV-specific CD4(+) cells and high numbers of CD8(+) T-cells, both before and during HAART. HIV-infected patients with HCMV disease had no HCMV-specific CD4(+) T-cells and extremely low levels of CD8(+) T-cells. Resolution of disease during HAART was associated with rescue of specific CD4(+) T-cells and a large increase in the specific CD8(+) T-cell count. Thus, HAART does not completely restore the normal immune function. In HIV-infected patients, sustained control of HCMV infection requires high frequencies of specific CD8(+) T-cells.

Distribution of killer cell immunoglobulin-like receptors genes in the Italian Caucasian population.

BACKGROUND: Killer cell immunoglobulin-like receptors (KIRs) are a family of inhibitory and activatory receptors that are expressed by most natural killer (NK) cells. The KIR gene family is polymorphic: genomic diversity is achieved through differences in gene content and allelic polymorphism. The number of KIR loci has been reported to vary among individuals, resulting in different KIR haplotypes. In this study we report the genotypic structure of KIRs in 217 unrelated healthy Italian individuals from 22 immunogenetics laboratories, located in the northern, central and southern regions of Italy. METHODS: Two hundred and seventeen DNA samples were studied by a low resolution PCR-SSP kit designed to identify all KIR genes. RESULTS: All 17 KIR genes were observed in the population with different frequencies than other Caucasian and non-Caucasian populations; framework genes KIR3DL3, KIR3DP1, KIR2DL4 and KIR3DL2 were present in all individuals. Sixty-five different profiles were found in this Italian population study. Haplotype A remains the most prevalent and genotype 1, with a frequency of 28.5%, is the most commonly observed in the Italian population. CONCLUSION: The Italian Caucasian population shows polymorphism of the KIR gene family like other Caucasian and non-Caucasian populations. Although 64 genotypes have been observed, genotype 1 remains the most frequent as already observed in other populations. Such knowledge of the KIR gene distribution in populations is very useful in the study of associations with diseases and in selection of donors for haploidentical bone marrow transplantation.

Spatial cognition based on geometry and landmarks in the domestic chick (Gallus gallus).

Recent evidence suggest that encoding of spatial information based on extended surfaces may differ from encoding based on discrete arrays of local elements. Here we investigated the use of these different frames of reference in domestic chicks. Chicks were trained to search for food hidden under sawdust in the center of the floor of a square-shaped landmark array, with its center in coincidence with the center of a square-shaped enclosure. Displacement of the array to a corner caused a shift of searching behavior toward the array, the search activity spanning between the center of the arena and the center of the array. After changing distances between landmarks, chicks still searched in the central area. Asymmetries were apparent in chicks tested in monocular conditions, with left-eyed chicks being more affected by the overall enclosure and right-eyed chicks by local landmarks. These results suggest that chicks can use both distances from extended surfaces and local information provided by the landmarks of the array to orient in space. However, chicks do not seem to perceive the array as a whole configuration, rather they tend to rely only on single landmarks to locate the goal.