The trapped-ion quantum charge-coupled device (QCCD) proposal
lays out a blueprint for a universal quantum computer that uses mobile ions as qubits. Analogous to a charge-coupled device (CCD) camera, ...which stores and processes imaging information as movable electrical charges in coupled pixels, a QCCD computer stores quantum information in the internal state of electrically charged ions that are transported between different processing zones using dynamic electric fields. The promise of the QCCD architecture is to maintain the low error rates demonstrated in small trapped-ion experiments
by limiting the quantum interactions to multiple small ion crystals, then physically splitting and rearranging the constituent ions of these crystals into new crystals, where further interactions occur. This approach leverages transport timescales that are fast relative to the coherence times of the qubits, the insensitivity of the qubit states of the ion to the electric fields used for transport, and the low crosstalk afforded by spatially separated crystals. However, engineering a machine capable of executing these operations across multiple interaction zones with low error introduces many difficulties, which have slowed progress in scaling this architecture to larger qubit numbers. Here we use a cryogenic surface trap to integrate all necessary elements of the QCCD architecture-a scalable trap design, parallel interaction zones and fast ion transport-into a programmable trapped-ion quantum computer that has a system performance consistent with the low error rates achieved in the individual ion crystals. We apply this approach to realize a teleported CNOT gate using mid-circuit measurement
, negligible crosstalk error and a quantum volume
of 2
= 64. These results demonstrate that the QCCD architecture provides a viable path towards high-performance quantum computers.
Population leakage outside the qubit subspace presents a particularly harmful source of error that cannot be handled by standard error correction methods. Using a trapped ^{171}Yb^{+} ion, we ...demonstrate an optical pumping scheme to suppress leakage errors in atomic hyperfine qubits. The selection rules and narrow linewidth of a quadrupole transition are used to selectively pump population out of leakage states and back into the qubit subspace. Each pumping cycle reduces the leakage population by a factor of ∼3, allowing for an exponential suppression in the number of cycles. We use interleaved randomized benchmarking on the qubit subspace to show that this pumping procedure has negligible side effects on the qubit subspace, bounding the induced qubit memory error by ≤2.0(8)×10^{-5} per cycle, and qubit population decay to ≤1.4(3)×10^{-7} per cycle. These results clear a major obstacle for implementations of quantum error correction and error mitigation protocols.
Quantum tomography is a critically important tool to evaluate quantum hardware, making it essential to develop optimized measurement strategies that are both accurate and efficient. We compare a ...variety of strategies using nearly pure test states. Those that are informationally complete for all states are found to be accurate and reliable even in the presence of errors in the measurements themselves, while those designed to be complete only for pure states are far more efficient but highly sensitive to such errors. Our results highlight the unavoidable trade-offs inherent in quantum tomography.
Understanding the flow of spins in magnetic layered structures has resulted in an increase in data storage density in hard drives over the past decade of more than two orders of magnitude. Following ...this remarkable success, the field of 'spintronics' or spin-based electronics is moving beyond effects based on local spin polarization and is turning towards spin-orbit interaction (SOI) effects, which hold promise for the production, detection and manipulation of spin currents, allowing coherent transmission of information within a device. Although SOI-induced spin transport effects have been observed in two- and three-dimensional samples, these have been subtle and elusive, often detected only indirectly in electrical transport or else with more sophisticated techniques. Here we present the first observation of a predicted 'spin-orbit gap' in a one-dimensional sample, where counter-propagating spins, constituting a spin current, are accompanied by a clear signal in the easily measured linear conductance of the system. We first introduce the class of phenomena we dub 'the one-dimensional spin-orbit gap' using a simple example adapted from ref. 10, then describe our experiment in detail and finally present a more elaborate model that captures most of the features seen in our data.
We screened fecal specimens of 4,758 bats from Ghana and 272 bats from 4 European countries for betacoronaviruses. Viruses related to the novel human betacoronavirus EMC/2012 were detected in 46 ...(24.9%) of 185 Nycteris bats and 40 (14.7%) of 272 Pipistrellus bats. Their genetic relatedness indicated EMC/2012 originated from bats.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•A capped (5,5) carbon nanotube has been analysed by the linear-scaling DFT code ONETEP.•The charge distribution varies very little with external fields, showing screening.•The calculation reports ...details of individual Kohn-Sham orbitals.•The highest occupied orbital and its distribution change with applied field.•The work function is part of an energy change from the cores, due to many-electron effects.
The apex region of a capped (5,5) carbon nanotube (CNT) has been modelled with the DFT package ONETEP, using boundary conditions provided by a classical calculation with a conducting surface in place of the CNT. Results from the DFT solution include the Fermi level and the physical distribution and energies of individual orbitals for the CNT tip. Application of an external electric field changes the orbital number of the highest occupied molecular orbital (HOMO) and consequently changes its distribution on the CNT.
Fetal hemoglobin (HbF) is regulated as a multigenic trait. By genome-wide association study, we confirmed that HBS1L-MYB intergenic polymorphisms (HMIP) and BCL11A polymorphisms are highly associated ...with HbF in Chinese β-thalassemia heterozygotes. In this population, the variance in HbF resulting from the HMIP is 13.5%; that resulting from the BCL11A polymorphism is 6.4%. To identify the functional variant in HMIP, we used 1000 Genomes Project data, single nucleotide polymorphism imputation, comparisons of association results across populations, potential transcription factor binding sites, and analysis of phylogenetic conservation. Based on these studies, a hitherto unreported association between HbF expression and a 3-bp deletion, between 135 460 326 and 135 460 328 bp on chromosome 6q23 was found. This 3-bp deletion is in complete linkage disequilibrium with rs9399137, which is the single nucleotide polymorphism in HMIP most significantly associated with HbF among Chinese, Europeans, and Africans. Chromatin immunoprecipitation assays confirmed erythropoiesis-related transcription factors binding to this region in K562 cells. Based on transient expression of a luciferase reporter plasmid, the DNA fragment encompassing the 3-bp deletion polymorphism has enhancer-like activity that is further augmented by the introduction of the 3-bp deletion. This 3-bp deletion polymorphism is probably the most significant functional motif accounting for HMIP modulation of HbF in all 3 populations.
We present a new and simplified two-qubit randomized benchmarking procedure that operates only in the symmetric subspace of a pair of qubits and is well suited for benchmarking trapped-ion systems. ...By performing benchmarking only in the symmetric subspace, we drastically reduce the experimental complexity, a number of gates required, and run time. The protocol is demonstrated on trapped ions using collective single-qubit rotations and the Mølmer-Sørenson (MS) interaction to estimate an entangling gate error of 2(1)×10^{−3}. We analyze the expected errors in the MS gate and find that the population remains mostly in the symmetric subspace. The errors that mix symmetric and antisymmetric subspaces appear as leakage and we characterize them by combining our protocol with recently proposed leakage benchmarking. Generalizations and limitations of the protocol are also discussed.
Background: Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to ...determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem
123Iβ-CIT SPECT and platelet
3Hparoxetine binding.
Methods: Drug-free depressed and healthy subjects were injected with 211 ± 22 MBq
123Iβ-CIT and imaged 24 ± 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V
3″ = (brainstem-occipital)/occipital), a measure proportional to the binding potential (B
max/K
d), was used for all comparisons.
Results: Results showed a statistically significant reduction in brainstem V
3″ values in depressed as compared to healthy subjects (3.1 ± .9 vs. 3.8 ± .8, p = .02). Platelet
3Hparoxetine binding was not altered (B
max = 2389 ± 484 vs. 2415 ± 538 fmol/mg protein,
p = .91) and was not significantly correlated with brainstem
123Iβ-CIT binding (
r = −0.14,
p = .48).
Conclusions: These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression.
Abstract Objective In 2008 GROINSS-V-I, the largest validation trial on the sentinel node (SN) procedure in vulvar cancer, showed that application of the SN-procedure in patients with early-stage ...vulvar cancer is safe. The current study aimed to evaluate long-term follow-up of these patients regarding recurrences and survival. Methods From 2000 until 2006 GROINSS-V-I included 377 patients with unifocal squamous cell carcinoma of the vulva (T1,<4 cm), who underwent the SN-procedure. Only in case of SN metastases an inguinofemoral lymphadenectomy was performed. For the present study follow-up was completed until March 2015. Results The median follow-up was 105 months (range 0–179). The overall local recurrence rate was 27.2% at 5 years and 39.5% at 10 years after primary treatment, while for SN-negative patients 24.6% and 36.4%, and for SN-positive patients 33.2% and 46.4% respectively (p = 0.03). In 39/253 SN-negative patients (15.4%) an inguinofemoral lymphadenectomy was performed, because of a local recurrence. Isolated groin recurrence rate was 2.5% for SN-negative patients and 8.0% for SN-positive patients at 5 years. Disease-specific 10-year survival was 91% for SN-negative patients compared to 65% for SN-positive patients (p < .0001). For all patients, 10-year disease-specific survival decreased from 90% for patients without to 69% for patients with a local recurrence (p < .0001). Conclusions Survival is very good for patients with a negative SN, but still 36% of these patients, as well as 46% of the patients with a positive SN, will have a local recurrence. Although a local recurrence is treated with curative intent, the disease-specific survival of these patients decreases significantly.
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