Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics—such as glass transitions and crystal nucleation1,2,3,4. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension—poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin—where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.

A colloidal model system with an interaction tunable from hard sphere to soft and dipolar

Trapped atomic ions are standards for quantum information processing, serving as quantum memories, hosts of quantum gates in quantum computers and simulators, and nodes of quantum communication networks. Quantum bits based on trapped ions enjoy a rare combination of attributes: They have exquisite coherence properties, they can be prepared and measured with nearly 100% efficiency, and they are readily entangled with each other through the Coulomb interaction or remote photonic interconnects. The outstanding challenge is the scaling of trapped ions to hundreds or thousands of qubits and beyond, at which scale quantum processors can outperform their classical counterparts in certain applications. We review the latest progress and prospects in that effort, with the promise of advanced architectures and new technologies, such as microfabricated ion traps and integrated photonics.

https://science.sciencemag.org/content/sci/339/6124/1164.full.pdf

Scaling the Ion Trap Quantum Processor

Trapped ions are among the most promising systems for practical quantum computing (QC). The basic requirements for universal QC have all been demonstrated with ions, and quantum algorithms using few-ion-qubit systems have been implemented. We review the state of the field, covering the basics of how trapped ions are used for QC and their strengths and limitations as qubits. In addition, we discuss what is being done, and what may be required, to increase the scale of trapped ion quantum computers while mitigating decoherence and control errors. Finally, we explore the outlook for trapped-ion QC. In particular, we discuss near-term applications, considerations impacting the design of future systems of trapped ions, and experiments and demonstrations that may further inform these considerations.

Trapped-ion quantum computing: Progress and challenges

Many creatures in nature, such as butterflies and peacocks, display unique brilliant colours, known as ‘structural colours’, which result from the interaction of light with periodic nanostructures on their surfaces. Mimicking such nanostructures found in nature, however, requires state-of-the-art nanofabrication techniques that are slow, expensive and not scalable. Herein, we demonstrate high-resolution patterning of multiple structural colours within seconds, based on successive tuning and fixing of colour using a single material along with a maskless lithography system. We have invented a material called ‘M-Ink’, the colour of which is tunable by magnetically changing the periodicity of the nanostructure and fixable by photochemically immobilizing those structures in a polymer network. We also demonstrate a flexible photonic crystal for the realization of structural colour printing. The simple, controllable and scalable structural colour printing scheme presented may have a significant impact on colour production for general consumer goods. Maskless high-resolution patterning of structural colours is demonstrated using a new material called ‘M-Ink’. The period of the material is patterned magnetically and a photochemical process immobilizes the structure in a polymer network.

Structural colour printing using a magnetically tunable and lithographically fixable photonic crystal

The practical construction of scalable quantum-computer hardware capable of executing nontrivial quantum algorithms will require the juxtaposition of different types of quantum systems. We analyze a modular ion trap quantum-computer architecture with a hierarchy of interactions that can scale to very large numbers of qubits. Local entangling quantum gates between qubit memories within a single register are accomplished using natural interactions between the qubits, and entanglement between separate registers is completed via a probabilistic photonic interface between qubits in different registers, even over large distances. We show that this architecture can be made fault tolerant, and demonstrate its viability for fault-tolerant execution of modest size quantum circuits.

Large-scale modular quantum-computer architecture with atomic memory and photonic interconnects

We present the design, fabrication and experimental implementation of surface ion traps with Y-shaped junctions. The traps are designed to minimize the pseudopotential variations in the junction region at the symmetric intersection of three linear segments. We experimentally demonstrate robust linear and junction shuttling with greater than 106 round-trip shuttles without ion loss. By minimizing the direct line of sight between trapped ions and dielectric surfaces, negligible day-to-day and trap-to-trap variations are observed. In addition to high-fidelity single-ion shuttling, multiple-ion chains survive splitting, ion-position swapping and recombining routines. The development of two-dimensional trapping structures is an important milestone for ion-trap quantum computing and quantum simulations.

http://iopscience.iop.org/article/10.1088/1367-2630/13/7/075018/pdf

Design, fabrication and experimental demonstration of junction surface ion traps

We report the results of a computer simulation of the evolution of structure in a two component fluid consisting of a liquid phase and a dispersed colloidal phase subjected to a uniaxial field. Our primary objective is to understand the mechanism and kinetics of coarsening and the emergence of crystallinity. Using an efficient, linear-N simulation method we report studies of systems of N=10 000 particles over the concentration range of 10–50 vol %. We present a variety of methods of characterizing the structures that emerge, including the anisotropy of the conductivity, capacitance and dipolar interaction energy, the two-dimensional pair correlation function, principal moments of the gyration tensor, velocity correlation functions, microcrystallinity and coordination number, and the optical attenuation length. We conclude that athermal coarsening is effectively driven by the presence of defect structures and that as the concentration increases, the structures progressively lose the well-known “chain” anis...

Simulation of the athermal coarsening of composites structured by a biaxial field

Through simulation and experiment we demonstrate that when a magnetic field is applied to a suspension of magnetic particles, the optical attenuation length along the direction of the field increases dramatically, due to the formation of chainlike structures that allow the transmission of light between the strongly absorbing particles. This phenomenon is interesting for two reasons; first, there might be practical applications for this effect, such as optical-fiber-based magnetic field sensors, and second, measuring the time evolution of the optical attenuation length enables us to determine the kinetics of structure formation, which can be compared to the predictions of simulation and theory. In agreement with both simulation and theory, the optical attenuation length increases as a power of time, but much less light is actually transmitted than expected, especially at higher particle concentrations. We conclude that particle roughness, which is not included in either theory or simulation, plays a significant role in structural development, by pinning structures into local minima. {copyright} {ital 1999} {ital The American Physical Society}

Magnetic-field-induced optical transmittance in colloidal suspensions.

Self-heating study of an AlGaN/GaN-based heterostructure field-effect

When a suspension of colloidal particles is subjected to a strong electric or magnetic field, the induced dipolar interactions will cause the particles to form organized structures, provided a sufficient permittivity or permeability mismatch exists, respectively, between the particles and the suspending liquid. A uniaxial field will produce uniaxial structures, and a biaxial field, such as a rotating field, will produce biaxial structures, and either of these structures can be pinned by polymerizing the continuous phase to produce field-structured composites. We have previously reported on the coarsening of field-structured composites in the absence of thermal effects, i.e., Brownian motion. Athermal simulations are primarily valid in describing the deep quenches that occur when the induced dipolar interactions between particles greatly exceed kBT. However, deep quenches can lead to kinetic structures that are far from equilibrium. By introducing Brownian motion we have shown that structures with signific...

Chris P. Tigges

Papers

Design, fabrication and experimental demonstration of junction surface ion traps

Simulation of the athermal coarsening of composites structured by a biaxial field

Magnetic-field-induced optical transmittance in colloidal suspensions.

Self-heating study of an AlGaN/GaN-based heterostructure field-effect

Thermal coarsening of uniaxial and biaxial field-structured composites