A microfabricated ion trap with integrated microwave circuitry

We describe the design, fabrication and testing of a surface-electrode ion trap, which incorporates microwave waveguides, resonators and coupling elements for the manipulation of trapped ion qubits using near-field microwaves. The trap is optimised to give a large microwave field gradient to allow state-dependent manipulation of the ions' motional degrees of freedom, the key to multiqubit entanglement. The microwave field near the centre of the trap is characterised by driving hyperfine transitions in a single laser-cooled 43Ca+ ion.Comment: 4 pages, 5 figure

Nonharmonic phonons in MgB_2 at elevated temperatures

Inelastic neutron scattering was used to measure phonon spectra in MgB_2 and Mg_(0.75)Al_(0.25)B_2 from 7 to 750 K to investigate anharmonicity and adiabatic electron-phonon coupling. First-principles calculations of phonons with a linear response method were performed at multiple unit cell volumes, and the Helmholtz free energy was minimized to obtain the lattice parameters and phonon dynamics at elevated temperature in the quasiharmonic approximation. Most of the temperature dependence of the phonon density of states could be understood with the quasiharmonic approximation, although there was also significant thermal broadening of the phonon spectra. In comparison to Mg_(0.75)Al_(0.25)B_2, in the energy range of 60 to 80 meV the experimental phonon spectra from MgB_2 showed a nonmonotonic change with temperature around 500 K. This may originate from a change with temperature of the adiabatic electron-phonon coupling

Deterministic entanglement and tomography of ion spin qubits

We have implemented a universal quantum logic gate between qubits stored in the spin state of a pair of trapped calcium 40 ions. An initial product state was driven to a maximally entangled state deterministically, with 83% fidelity. We present a general approach to quantum state tomography which achieves good robustness to experimental noise and drift, and use it to measure the spin state of the ions. We find the entanglement of formation is 0.54.Comment: 3 figures, 4 pages, footnotes fixe

Long-lived mesoscopic entanglement outside the Lamb-Dicke regime

We create entangled states of the spin and motion of a single $^{40}$Ca$^+$ ion in a linear ion trap. The motional part consists of coherent states of large separation and long coherence time. The states are created by driving the motion using counterpropagating laser beams. We theoretically study and experimentally observe the behaviour outside the Lamb-Dicke regime, where the trajectory in phase space is modified and the coherent states become squeezed. We directly observe the modification of the return time of the trajectory, and infer the squeezing. The mesoscopic entanglement is observed up to $\Delta \alpha = 5.1$ with coherence time 170 microseconds and mean phonon excitation \nbar = 16.Comment: 5 pages, 3 figures. Revised version after editor comment

Absence of long-range chemical ordering in equimolar FeCoCrNi

Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order