Angle-robust Two-Qubit Gates in a Linear Ion Crystal

In trapped-ion quantum computers, two-qubit entangling gates are generated by applying spin-dependent force which uses phonons to mediate interaction between the internal states of the ions. To maintain high-fidelity two-qubit gates under fluctuating experimental parameters, robust pulse-design methods are applied to remove the residual spin-motion entanglement in the presence of motional mode frequency drifts. Here we propose an improved pulse-design method that also guarantees the robustness of the two-qubit rotation angle against uniform mode frequency drifts by combining pulses with opposite sensitivity of the angle to mode frequency drifts. We experimentally measure the performance of the designed gates and see an improvement on both gate fidelity and gate performance under uniform mode frequency offsets.Comment: 10 pages, 11 figure

Repetitive readout and real-time control of nuclear spin qubits in 171^{171}Yb atoms

We demonstrate high fidelity repetitive projective measurements of nuclear spin qubits in an array of neutral ytterbium-171 ($^{171}$Yb) atoms. We show that the qubit state can be measured with a fidelity of 0.995(4) under a condition that leaves it in the state corresponding to the measurement outcome with a probability of 0.993(6) for a single tweezer and 0.981(4) averaged over the array. This is accomplished by near-perfect cyclicity of one of the nuclear spin qubit states with an optically excited state under a magnetic field of $B=58$ G, resulting in a bright/dark contrast of $\approx10^5$ during fluorescence readout. The performance improves further as $\sim1/B^2$. The state-averaged readout survival of 0.98(1) is limited by off-resonant scattering to dark states and can be addressed via post-selection by measuring the atom number at the end of the circuit, or during the circuit by performing a measurement of both qubit states. We combine projective measurements with high-fidelity rotations of the nuclear spin qubit via an AC magnetic field to explore several paradigmatic scenarios, including the non-commutivity of measurements in orthogonal bases, and the quantum Zeno mechanism in which measurements "freeze" coherent evolution. Finally, we employ real-time feedforward to repetitively deterministically prepare the qubit in the $+z$ or $-z$ direction after initializing it in an orthogonal basis and performing a projective measurement in the $z$-basis. These capabilities constitute an important step towards adaptive quantum circuits with atom arrays, such as in measurement-based quantum computation, fast many-body state preparation, holographic dynamics simulations, and quantum error correction

Rice plants respond to ammonium‐stress by adopting a helical root growth pattern

High levels of ammonium nutrition reduce plant growth and different plant species have developed distinct strategies to maximize ammonium acquisition while alleviate ammonium toxicity through modulating root growth. Up to now, the mechanism underlying plant tolerance or sensitivity towards ammonium remain unclear. Rice uses ammonium as its main N source. Here we show that ammonium supply restricts rice root elongation and induces a helical growth pattern, which is attributed to root acidification resulting from ammonium uptake. Ammonium-induced low pH triggers asymmetric auxin distribution in rice root tips through changes in auxin signaling, thereby inducing a helical growth response. Blocking auxin signaling completely inhibited this root response. In contrast, this root response is not activated in ammonium-treated Arabidopsis. Acidification of Arabidopsis roots leads to the protonation of IAA, and dampening the intracellular auxin signaling levels that are required for maintaining root growth. Our study suggests a different mode of action by ammonium on the root pattern and auxin response machinery in rice versus Arabidopsis, and the rice-specific helical root response towards ammonium is an expression of the ability of rice in moderating auxin signaling and root growth to utilize ammonium while confronting acidic stress

Statistics of Data Reduction and Structure Refinement.

a<p>Data for the highest resolution bin is in parentheses.</p>b<p><i>R</i>_merge = Σ|Ii−Im|/ΣIi, where Ii is the intensity of the measured reflection and Im is the mean intensity of all symmetry-related reflections.</p>c<p><i>R</i>_work = Σ| |Fobs|−|Fcalc| |/Σ|Fobs|, where Fobs and Fcalc are observed and calculated structure factors, respectively. <i>R</i>_free = Σ_T| |Fobs|−|Fcalc| |/Σ_T|Fobs|, where T denotes a test data set of about 5% of the total reflections randomly chosen and set aside prior to refinement.</p>d<p>RMSD = root-mean-square deviation.</p

The Crystal Structure of <em>Arabidopsis</em> VSP1 Reveals the Plant Class C-Like Phosphatase Structure of the DDDD Superfamily of Phosphohydrolases

<div><p><em>Arabidopsis thaliana</em> vegetative storage proteins, VSP1 and VSP2, are acid phosphatases and belong to the haloacid dehalogenase (HAD) superfamily. In addition to their potential nutrient storage function, they were thought to be involved in plant defense and flower development. To gain insights into the architecture of the protein and obtain clues about its function, we have tested their substrate specificity and solved the structure of VSP1. The acid phosphatase activities of these two enzymes require divalent metal such as magnesium ion. Conversely, the activity of these two enzymes is inhibited by vanadate and molybdate, but is resistant to inorganic phosphate. Both VSP1 and VSP2 did not exhibit remarkable activities to any physiological substrates tested. In the current study, we presented the crystal structure of recombinant VSP1 at 1.8 Å resolution via the selenomethionine single-wavelength anomalous diffraction (SAD). Specifically, an α-helical cap domain on the top of the α/β core domain is found to be involved in dimerization. In addition, despite of the low sequence similarity between VSP1 and other HAD enzymes, the core domain of VSP1 containing conserved active site and catalytic machinery displays a classic haloacid dehalogenase fold. Furthermore, we found that VSP1 is distinguished from bacterial class C acid phosphatase P4 by several structural features. To our knowledge, this is the first study to reveal the crystal structure of plant vegetative storage proteins.</p> </div

Relative activities of VSP1 and VSP2 toward different substrates.

<p>ND, not detectable.</p><p>Relative activities are expressed as the percentage of the activity with <i>p</i>NPP. The results are the average of the values determined in triplicates and the respective standard error is constantly lower than 10%.</p

Comparison between VSP1 and P4 in active sites and dimer patterns.

<p>(A) Residues in the catalytic site of VSP1. Magnesium ions and water molecules are colored by green and red, respectively. (B) Residues in the catalytic site of P4. Magnesium ion and water molecules are colored by green and red, respectively. (C) Hydrophobic core between two VSP1 monomers. Two VSP1 monomers are colored magenta and cyan, respectively. (D) Hydrogen bonds between two VSP1 monomers. Two VSP1 monomers are colored magenta and cyan, respectively. (E) Interaction pattern of VSP1 dimer. One monomer is coloured magenta, while the N-terminal helices of the other monomer are coloured cyan. (F) Interaction pattern of P4 dimer. One monomer is colored yellow, while the N-terminal helices of the other monomer are colored green. The magenta VSP1 monomer in (E) and the yellow P4 monomer in (F) are aligned.</p

Structural comparison of VSP1 and P4.

<p>(A) Topology of VSP1. (B) Topology of P4. (C) Superposition of VSP1 and P4 (stereo view). In (A) (B) (C), an additional α helix in P4 (yellow) is marked by a rectangle. Longer N-terminus in VSP1 (cyan) is colored blue, while longer C-terminus in P4 is colored magenta. Structural elements of P4 in (B) are labeled based on the structural alignment with VSP1. (D) NMN binding with P4. NMN is shown in sticks model. Important residues of P4 interacting with NMN are labeled. (E) Superpose VSP1 to P4 while NMN is modeled at the same site as in P4. Corresponding residues in VSP1 are labeled. NMN is shown in sticks model.</p

Kinetic parameters for VSP1 protein with different divalent metal ions.

<p>Data represent the means±SD from three independent assays.</p