System Bits: Oct. 13

Quantum computing hurdle cleared
Clearing what they say is the final hurdle to making silicon-based quantum computers a reality, a team of University of New South Wales researchers has built a quantum logic gate in silicon for the first time, making calculations between two qubits of information possible.

Team leader Andrew Dzurak, Scientia Professor and Director of the Australian National Fabrication Facility at UNSW said, “What we have is a game changer. We’ve demonstrated a two-qubit logic gate – the central building block of a quantum computer – and, significantly, done it in silicon. Because we use essentially the same device technology as existing computer chips, we believe it will be much easier to manufacture a full-scale processor chip than for any of the leading designs, which rely on more exotic technologies. This makes the building of a quantum computer much more feasible, since it is based on the same manufacturing technology as today’s computer industry,” he added.

Lead author Menno Veldhorst (left) and project leader Andrew Dzurak (right) in the UNSW laboratory where the experiments were performed. (Source: University of New South Wales)

In classical computers, data is rendered as binary bits, which are always in one of two states: 0 or 1. However, a quantum bit (or ‘qubit’) can exist in both of these states at once, a condition known as a superposition. A qubit operation exploits this quantum weirdness by allowing many computations to be performed in parallel (a two-qubit system performs the operation on 4 values, a three-qubit system on 8, and so on). 

If quantum computers are to become a reality, the ability to conduct one- and two-qubit calculations is essential but until now, it had not been possible to make two quantum bits ‘talk’ to each other – and thereby create a logic gate – using silicon. The UNSW team worked with Professor Kohei M. Itoh of Japan’s Keio University on the project that they said means that all of the physical building blocks for a silicon-based quantum computer have now been successfully constructed, allowing engineers to finally begin the task of designing and building a functioning quantum computer.

The UNSW approach reconfigured the ‘transistors’ used to define the bits in existing silicon chips, and turned them into qubits. The silicon transistors were morphed into quantum bits by ensuring that each has only one electron associated with it. The binary code of 0 or 1 was stored on the ‘spin’ of the electron, which is associated with the electron’s tiny magnetic field.

Further, the team had recently patented a design for a full-scale quantum computer chip that would allow for millions of the qubits, all doing the types of calculations that they’ve experimentally demonstrated. A key next step for the project is to identify the right industry partners to work with to manufacture the full-scale quantum processor chip. They expect a full-scale quantum processor would have major applications in the finance, security and healthcare sectors, allowing the identification and development of new medicines by greatly accelerating the computer-aided design of pharmaceutical compounds (and minimizing lengthy trial and error testing); the development of new, lighter and stronger materials spanning consumer electronics to aircraft; and faster information searching through large databases.

Electron resonator
Resonators are an important tool in physics, as the curved mirrors inside them usually focus light waves that act, for instance, on atoms. To this end, physicists at ETH Zurich have built a resonator for electrons and to direct the standing waves thus created onto an artificial atom.

Electron microscope image of the ETH Zurich experiment. Between the quantum dot (left) and the curved electrode (right) electronic standing waves arise, which interact with the electrons of the quantum dot. (Source: ETH Zurich)

Today curved or parabolic mirrors are used in a range of technical applications ranging from satellite dishes to laser resonators, where light waves are amplified between two mirrors. Modern quantum physics also makes use of resonators with curved mirrors. In order to study single atoms, for example, researchers use the light focused by the mirrors to enhance the interaction between the light waves and the atoms.

The ETH Zurich-developed resonator could be used for constructing quantum computers and for investigating many-body effects in solids, the researchers said.

Evaporative patterning
Believe it or not, understanding how coffee rings form could help engineers design better optical systems, according to Harvard University researchers.

They explained that evaporating liquids often leave behind a residue of particles that can be shaped in concentric bands, like coffee rings, uniform films like soup stains, or more intricate patterns like the salt left over from snow melt or the above colloidal deposits, and the mechanisms behind the different patterning types has remained largely mysterious until now.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have unlocked the dynamics of evaporative patterning, revealing that the type of patterns left behind depends on the evaporation rate, particle density, fluid viscosity and surface forces between the liquid and the substrate. 

They said understanding the dynamics of evaporative patterning is important because evaporation is a commonly used technique to assemble particles that are too small to manipulate individually, such as colloids, and to synthesize functional interfaces with unusual optical and mechanical properties.