Navigating the 16-dimensional Hilbert space of a high-spin donor qudit with electric and magnetic fields.

Efficient scaling and flexible control are key aspects of useful quantum computing hardware. Spins in semiconductors combine quantum information processing with electrons, holes or nuclei, control with electric or magnetic fields, and scalable coupling via exchange or dipole interaction. However, accessing large Hilbert space dimensions has remained challenging, due to the short-distance nature of the interactions. Here, we present an atom-based semiconductor platform where a 16-dimensional Hilbert space is built by the combined electron-nuclear states of a single antimony donor in silicon. We demonstrate the ability to navigate this large Hilbert space using both electric and magnetic fields, with gate fidelity exceeding 99.8% on the nuclear spin, and unveil fine details of the system Hamiltonian and its susceptibility to control and noise fields. These results establish high-spin donors as a rich platform for practical quantum information and to explore quantum foundations.

An electrically driven single-atom "flip-flop" qubit.

The spins of atoms and atom-like systems are among the most coherent objects in which to store quantum information. However, the need to address them using oscillating magnetic fields hinders their integration with quantum electronic devices. Here, we circumvent this hurdle by operating a single-atom "flip-flop" qubit in silicon, where quantum information is encoded in the electron-nuclear states of a phosphorus donor. The qubit is controlled using local electric fields at microwave frequencies, produced within a metal-oxide-semiconductor device. The electrical drive is mediated by the modulation of the electron-nuclear hyperfine coupling, a method that can be extended to many other atomic and molecular systems and to the hyperpolarization of nuclear spin ensembles. These results pave the way to the construction of solid-state quantum processors where dense arrays of atoms can be controlled using only local electric fields.

Precision tomography of a three-qubit donor quantum processor in silicon.

Nuclear spins were among the first physical platforms to be considered for quantum information processing1,2, because of their exceptional quantum coherence3 and atomic-scale footprint. However, their full potential for quantum computing has not yet been realized, owing to the lack of methods with which to link nuclear qubits within a scalable device combined with multi-qubit operations with sufficient fidelity to sustain fault-tolerant quantum computation. Here we demonstrate universal quantum logic operations using a pair of ion-implanted 31P donor nuclei in a silicon nanoelectronic device. A nuclear two-qubit controlled-Z gate is obtained by imparting a geometric phase to a shared electron spin4, and used to prepare entangled Bell states with fidelities up to 94.2(2.7)%. The quantum operations are precisely characterized using gate set tomography (GST)5, yielding one-qubit average gate fidelities up to 99.95(2)%, two-qubit average gate fidelity of 99.37(11)% and two-qubit preparation/measurement fidelities of 98.95(4)%. These three metrics indicate that nuclear spins in silicon are approaching the performance demanded in fault-tolerant quantum processors6. We then demonstrate entanglement between the two nuclei and the shared electron by producing a Greenberger-Horne-Zeilinger three-qubit state with 92.5(1.0)% fidelity. Because electron spin qubits in semiconductors can be further coupled to other electrons7-9 or physically shuttled across different locations10,11, these results establish a viable route for scalable quantum information processing using donor nuclear and electron spins.

Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper-Bound to 99.85% by Ion-Solid Interactions.

Silicon chips containing arrays of single dopant atoms can be the material of choice for classical and quantum devices that exploit single donor spins. For example, group-V donors implanted in isotopically purified 28 Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31 P, hyperfine clock transitions in 209 Bi or electrically controllable 123 Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here, an on-chip detector electrode system with 70 eV root-mean-square noise (≈20 electrons) is employed to demonstrate near-room-temperature implantation of single 14 keV 31 P+ ions. The physics model for the ion-solid interaction shows an unprecedented upper-bound single-ion-detection confidence of 99.85 ± 0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31 P+ implants, a yield limit of 98.1% is demonstrated. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single-ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices.

Conditional quantum operation of two exchange-coupled single-donor spin qubits in a MOS-compatible silicon device.

Silicon nanoelectronic devices can host single-qubit quantum logic operations with fidelity better than 99.9%. For the spins of an electron bound to a single-donor atom, introduced in the silicon by ion implantation, the quantum information can be stored for nearly 1 second. However, manufacturing a scalable quantum processor with this method is considered challenging, because of the exponential sensitivity of the exchange interaction that mediates the coupling between the qubits. Here we demonstrate the conditional, coherent control of an electron spin qubit in an exchange-coupled pair of 31P donors implanted in silicon. The coupling strength, J = 32.06 ± 0.06 MHz, is measured spectroscopically with high precision. Since the coupling is weaker than the electron-nuclear hyperfine coupling A ≈ 90 MHz which detunes the two electrons, a native two-qubit controlled-rotation gate can be obtained via a simple electron spin resonance pulse. This scheme is insensitive to the precise value of J, which makes it suitable for the scale-up of donor-based quantum computers in silicon that exploit the metal-oxide-semiconductor fabrication protocols commonly used in the classical electronics industry.

Reproducible and stable cycling performance data on secondary zinc oxygen batteries.

Electrically rechargeable zinc oxygen batteries are promising energy storage devices. They appeal due to the abundance of zinc metal and their high energy density. Research on zinc oxygen batteries is currently focusing on the development of electrode materials. Since the progress is rapid and no state-of-the-art is agreed upon yet, it is difficult to benchmark their performance. This circumstance also complicates the use of the generated electrochemical data for model-based research - simulating the processes in the battery requires reliable performance data and material properties from experimental investigations. Herein we describe reproducible data on the cycling performance and durability of zinc oxygen batteries. We utilize anodes and gas diffusion electrodes (with the bifunctional catalysts Sr2CoO3Cl, Ru-Sn oxide, and Fe0.1Ni0.9Co2O4 with activated carbon) with low degradation during cycling, and present voltage data of current-dependent discharge and charge. All in all, we stimulate to reuse the data for parameter fitting in model-based work, and also to evaluate novel battery materials by preventing or minimizing side reactions with the testing protocol and setup utilized.

Controllable freezing of the nuclear spin bath in a single-atom spin qubit.

The quantum coherence and gate fidelity of electron spin qubits in semiconductors are often limited by nuclear spin fluctuations. Enrichment of spin-zero isotopes in silicon markedly improves the dephasing time [Formula: see text], which, unexpectedly, can extend two orders of magnitude beyond theoretical expectations. Using a single-atom 31P qubit in enriched 28Si, we show that the abnormally long [Formula: see text] is due to the freezing of the dynamics of the residual 29Si nuclei, caused by the electron-nuclear hyperfine interaction. Inserting a waiting period when the electron is controllably removed unfreezes the nuclear dynamics and restores the ergodic [Formula: see text] value. Our conclusions are supported by a nearly parameter-free modeling of the 29Si nuclear spin dynamics, which reveals the degree of backaction provided by the electron spin. This study clarifies the limits of ergodic assumptions in nuclear bath dynamics and provides previously unidentified strategies for maximizing coherence and gate fidelity of spin qubits in semiconductors.

Backbone modifications in peptidic inhibitors of flaviviral proteases.

The NS2B-NS3 protease is a promising target for the development of drugs against dengue virus (DENV), West Nile virus (WNV) and related flaviviruses. We report the systematic variation of the peptide backbone of the two lead compounds Bz-Arg-Lys-d-Phg-NH2 and Bz-Arg-Lys-d-Phg(OBn)-NH2. While inhibitory activity against WNV protease was generally decreased, the inhibitory potency against DENV protease could be conserved and increased in several peptidomimetics, particularly in those containing a (NMe)arginine fragment or an N-terminal α-keto amide. Methylation at the α-position of the C-terminal phenylglycine led to a 6-fold higher potency against DENV protease. Peptidomimetics with modified backbone showed increased resistance against hydrolytic attack by trypsin and α-chymotrypsin.

Synthesis of [{AgO2CCH2OMe(PPh3)} n ] and theoretical study of its use in focused electron beam induced deposition.

The synthesis, chemical and physical properties of [{AgO2CCH2OMe} n ] (1) and [{AgO2CCH2OMe(PPh3)} n ] (2) are reported. Consecutive reaction of AgNO3 with HO2CCH2OMe gave 1, which upon treatment with PPh3 produced 2. Coordination compound 2 forms a 1D coordination polymer in the solid state as evidenced by single crystal X-ray structure analysis. The coordination geometry at Ag+ is of the [3 + 1] type, whereby the carboxylate anions act as bridging ligands. The formation of PPh3-Ag(I) coordinative bonds results in distorted T-shaped AgPO2 units, which are stabilized further by an additional O-Ag dative bond. TG and TG-MS measurements show that 1 and 2 decompose at 190-250 °C (1) and 260-300 °C (2) via decarboxylation, involving Ag-P (2), C-C and C-O bond cleavages to give elemental silver as confirmed by PXRD studies. In order to verify if polymeric 2 is suitable as a FEBID precursor for silver deposition, its vapor pressure was determined (p170 °C = 5.318 mbar, ∆Hvap = 126.1 kJ mol-1), evincing little volatility. Also EI and ESI mass spectrometric studies were carried out. The dissociation of the silver(I) compound 2 under typical electron-driven FEBID conditions was studied by DFT (B3LYP) calculations on monomeric [AgO2CCH2OMe(PPh3)]. At an energy of the secondary electrons up to 0.8 eV elimination of PPh3 occurs, giving Ag+ and O2CCH2OMe-. Likewise, by release of PPh3 from [AgO2CCH2OMe(PPh3)] the fragment [AgO2CCH2OMe]- is formed from which Ag+ and O2CCH2OMe- is generated, further following the first fragmentation route. However, at 1.3 eV the initial step is decarboxylation giving [AgCH2OMe(PPh3)], followed by Ag-P and Ag-C bond cleavages.

Crystal structure of an unknown tetra-hydro-furan solvate of tetra-kis-(µ 3-cyanato-κ(3) N:N:N)tetra-kis-[(triphenyl-phosphane-κP)-silver(I)].

In the title compound, [{[(C6H5)3P]Ag}4{NCO}4], a distorted Ag4N4-heterocubane core is set up by four Ag(I) ions being coordinated by the N atoms of the cyanato anions in a µ 3-bridging mode. In addition, a tri-phenyl-phosphine ligand is datively bonded to each of the Ag(I) ions. Intra-molecular Ag⋯Ag distances as short as 3.133 (9) Šsuggest the presence of argentophilic (d (10)⋯d (10)) inter-actions. Five moderate-to-weak C-H⋯O hydrogen-bonding inter-actions are observed in the crystal structure, spanning a three-dimensional network. A region of electron density was treated with the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9-18] following unsuccessful attempts to model it as being part of disordered tetra-hydro-furan solvent mol-ecules. The given chemical formula and other crystal data do not take into account these solvent mol-ecules.

Hybrid Hairy Janus Particles Decorated with Metallic Nanoparticles for Catalytic Applications.

We report for the first time on the design of an advanced hairy hybrid Janus-type catalyst, which is comprised of an inorganic silica core covered with two distinct polymeric shells (hydrophilic and hydrophobic) on its opposite sides, while the catalytic species (in our case silver or gold nanoparticles) are immobilized directly into the hydrophilic stimuli-responsive polymer shell. The primary 200 nm large Janus particles with poly(acrylic acid) serving as the hydrophilic and polystyrene as the hydrophobic polymer were synthesized through a Pickering emulsion and a combination of "grafting from"/"grafting to" approaches. The incorporation of silver and gold nanoparticles within the hydrophilic polymer shell was achieved by infiltrating the respective metal ions into the polymer matrix, and nanoparticles were formed upon the addition of a reducing agent (triethylamine). Plasmon absorptions typical for silver and gold nanostructures were observed on the functionalized Janus particles using UV-vis spectroscopy. The respective systems were investigated by TEM and cryo-TEM revealing that the incorporated nanoparticles are selectively localized on the poly(acrylic acid) side of the Janus particles. The efficiency of the catalyst as well as the accessibility of the incorporated nanoparticles was tested on the reduction of Methylene Blue, Eosin Y, and 4-nitrophenol as convenient benchmark systems. Ultimately, the hairy Janus particles with immobilized Ag or Au nanoparticles efficiently catalyzed the respective reactions by applying extremely low amounts of catalyst. Finally, we demonstrated several advantages of the use of JPs with immobilized metallic nanoparticles, which are (i) JPs stabilize the emulsions, (ii) the emulsion can be destabilized by utilizing responsive properties of the JPs, and (iii) JPs can easily be recovered after reaction and reused again.

Crystal structure of cyclo-bis-(µ4-2,2-di-allyl-malonato-κ(6) O (1),O (3):O (3):O (1'),O (3'):O (1'))tetra-kis-(triphenyl-phosphane-κP)tetra-silver(I).

In the tetra-nuclear mol-ecule of the title compound, [Ag4(C9H10O4)2(C18H15P)4], the Ag(I) ion is coordinated by one P and three O atoms in a considerably distorted tetra-hedral environment. The two 2,2-di-allyl-malonate anions bridge four Ag(I) ions in a µ4-(κ(6) O (1),O (3):O (3):O (1'),O (3'):O (1')) mode, setting up an Ag4O8P4 core (point group symmetry -4..) of corner-sharing tetra-hedra. The shortest intra-molecular Ag⋯Ag distance of 3.9510 (3) Šreveals that no direct d (10)⋯d (10) inter-actions are present. Four weak intra-molecular C-H⋯O hydrogen bonds are observed in the crystal structure of the title compound, which most likely stabilize the tetra-nuclear silver core.

Nanoscale magneto-structural coupling in as-deposited and freestanding single-crystalline Fe7Pd3 ferromagnetic shape memory alloy thin films.

Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite-austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite-austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime.

Tailoring substrates for long-term organotypic culture of adult neuronal tissue.

Organotypic tissue cultures are highly promising for performing in vivo type studies in vitro. Currently, however, very limited survival times of only a few days for adult tissue often severely limit their application. Here, superhydrophilic nanostructured substrates with ideal material properties ensure tissue adhesion, essential for organotypic culture, while migration of single cells out of the tissue is hampered. Tuning substrate properties, for the first time, adult neuronal tissue could be cultured for 14 days with no indications of degeneration.

Cytotoxicity of hydrophylic silver carboxylato complexes.

BACKGROUND: Gold(I) and platinum(II) d(10) and d(8) electronic complexes such as (Au(PPh(2)CH(2)CH(2)PPh(2))(2))Cl and cisplatin, ((H(3)N)(2)PtCl(2)), possess strong antineoplastic activities. Almost no information is available regarding the anticancer activity of isoelectronic silver(I) d(10) complexes. This study examined the cytotoxicity of stable water-soluble silver(I) carboxylates. The results were related to the cytotoxicity of cisplatin and (Au(PPh(2)CH(2)CH(2)PPh(2))(2))Cl. MATERIALS AND METHODS: The silver carboxylates (AgO(2)CCH(2)OCH(3)), 1, (AgO(2)C-CH(2)OCH(2)CH(2)OCH(3)), 2, and (AgO(2)CCH(2)OCH(2)CH(2)OCH(2)CH(2)OCH(3)), 3, were investigated. Cytotoxicity tests were performed on the HeLa (human cervix epitheloid) cancer cell line, resting lymphocytes and PHA (phytohaemagglutinin)-stimulated lymphocyte cultures. Cell survival was measured by means of the colorometric 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide (MTT) assay. RESULTS: The IC(50) (50% cell growth inhibition) values of 1-3 in the HeLa cells varied between 2.6 and 6.1 µmol dm(-3) with being 1 the most cytotoxic silver complex. Drug activity was inversely proportional to the length of the carboxylato chain length. Complexes 1-3 were 3-5 times more cytotoxic against the HeLa cancer cells than against the PHA stimulated lymphocyte cultures. CONCLUSION: A drug activity-structure relationship exists in that short-chain silver carboxylates are more cytotoxic than long-chain silver carboxylates, but silver d(10) complexes are one order of magnitude less cytotoxic than platinum(II) d(8) or gold(I) d(10) complexes.

Cytotoxicity of ferrocenyl-ethynyl phosphine metal complexes of gold and platinum.

BACKGROUND: Ferrocene derivatives may possess antineoplastic activity. Those with low ferrocenyl reduction potentials often have the highest anticancer activity, as cell components have to oxidise them to the active ferrocenium species before cytotoxicity can be recorded. Some gold(I) complexes also possess anticancer activity. This study examined the cytotoxicity of ferrocenyl-ethynyl and ruthenocenyl-ethynyl complexes of gold and platinum. The results were related to the ease of iron oxidation in the ferrocenyl fragment and compared with the cytotoxicity of cisplatin, [(H(3)N)(2)PtCl(2)] and [Au(PPh(2)CH(2)CH(2)PPh(2))(2)]Cl. MATERIALS AND METHODS: Ferrocene-containing gold and platinum complexes of the type Fc-C≡C-PPh(2), 1, and Fc-C≡C-PPh(2)→M with Fc=ferrocenyl (Fe(II)(η(5)-C(5)H(5)) (η(5)-C(5)H(4))), Ph=phenyl (C(6)H(5)) and M=Au-Cl, 2, Au-C≡C-Fc, 3, or Au-C≡C-Rc, 4 (Rc=ruthenocenyl, (Ru(II)(η(5)-C(5)H(5)) (η(5)-C(5)H(4))) and the complex [(Fc-C≡C-PPh(2))(2)PtCl(2)], 5, were investigated. Cytotoxicity tests were determined on the HeLa (human cervix epitheloid) cancer cell line, ATCC CCL-2. Cell survival was measured by means of the colorometric 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide assay. RESULTS: The IC(50) values of compounds 1-4 from four experiments causing 50% cell growth inhibition, ranged between 4.6 and 27 µmol dm(-3). Drug activity was inversely proportional to the sum of all formal reduction potentials, E(o'), of the ferrocenyl groups of the Fc-C≡C-PPh(2) and Fc-C≡C-ligands coordinated to the gold centre. The Fc-C≡C-PPh(2)→Au-Cl complex, compound 2, was most cytotoxic with IC(50)=4.6 µmol dm(-3) , demonstrating the beneficial effect the Cl(-) ion has on the cytotoxicity of these neutral gold complexes. The platinum complex [(Fc-C≡C-PPh(2))(2)PtCl(2)], compound 5, resembling the structure of cisplatin, in principle should exhibit good cytotoxicity, but was not tested due to its total insolubility in any biocompatible medium.

(1-Ferrocenyl-4,4,4-trifluoro-butane-1,3-dionato-κO,O)bis-(triphenyl-phosphane)copper(I).

In the title mononuclear coordination complex, [CuFe(C(5)H(5))(C(9)H(5)F(3)O(2))(C(18)H(15)P)(2)], the Cu(I) ion is coordinated by the chelating ß-diketonate 1-ferrocenyl-4,4,4-trifluoro-butane-1,3-dione ligand through two O atoms and the two datively bonded triphenyl-phosphane ligands resulting in a distorted tetra-hedral coordination sphere. The Cu(I) ion, together with its chelating butane-1,3-dione group, is mutually coplanar [greatest displacement of an atom from this plane = 0.037 (1) Å], and the Cu(I) ion lies slightly above [0.013 (1) Å] the plane. The overall geometry, including the bond distances and angles within the complex, corresponds to those of other reported copper(I) ß-diketon-ates featuring organic groups at the ß-diketonate ligand.

Phosphite copper(I) trifluoroacetates [((RO)3P)mCuO2CCF3] (m = 1, 2, 3): synthesis, solid state structures and their potential use as CVD precursors.

Metal-organics [((RO)(3)P)(m)CuO(2)CCF(3)] (R = CH(3): 11a, m = 1; 11b, m = 2; 11c, m = 3. R = CH(2)CH(3): 12a, m = 1; 12b, m = 2; 12c, m = 3. R = CH(2)CF(3): 13a, m = 1; 13b, m = 2; 13c, m = 3) are either accessible by the reaction of [((RO)(3)P)(m)CuCl] (R = CH(3): 5a, m = 1; 5b, m = 2; 5c, m = 3. R = CH(2)CH(3): 6a, m = 1; 6b, m = 2; 6c, m = 3) with [KO(2)CCF(3)] (7), or treatment of [Cu(2)O] (8) with HO(2)CCF(3) (9) and P(OR)(3) (2, R = CH(3); 3, R = CH(2)CH(3); 4, R = CH(2)CF(3)). (31)P{(1)H} NMR spectra [((CH(3)O)(3)P)(m)CuO(2)CCF(3)] (m = 1, 1.5, 2, 2.5, 3, 3.5, and 4) have been studied at 25 and -80 °C showing phosphite ligand exchange in solution. The molecular structures of 11a and 13a-13c in the solid state are reported. Complexes 11a and 13a are tetramers featuring µ-η(2)(1κO:2κO')- and µ(3)-η(2)(1κO:2κO':3κO')-(11a) or µ(3)-η(2)(1κO:2κO':3κO')-bonded O(2)CCF(3) ligands (13a) with the Cu(I) ions being part of CuPO(2) and CuPO(3) units (11a), while in 13a solely a CuPO(3) moiety is present. Skeletal isomerism of 11a vs. 13a is discussed. Compound 13b is dimeric ({CuP(2)O(2)}(2)) with pseudo-tetrahedral Cu environments and µ-η(2)(1κO:2κO')O(2)CCF(3) functionalities. In monomeric 13c the O(2)CCF(3) ligand is η(1)(κO)-bonded to a tetra-coordinated Cu(i) ion. The thermal solid state properties of 11, 12 and 13 were studied by Thermo Gravimetry (TG). These complexes decompose by phosphite elimination, decarboxylation and dealkylation. Hot-wall Chemical Vapour Deposition (CVD) experiments were carried out at 380 °C using 11c as precursor for the deposition of copper onto pieces of TiN-coated oxidized silicon substrates. Copper layers of high purity were obtained with grain sizes between 200-1200 nm.