Power/Performance Bits: May 12

Quantum teleportation on a chip

Researchers at the University of Tokyo have successfully integrated the core circuits of quantum teleportation, which generate and detect quantum entanglement, into silica-optical-waveguide circuits on a silicon photonic chip measuring 0.0001 square meters.

While there has been significant progress in current technology of information processing, its performance is said to be reaching the fundamental limit of classical physics. On the other hand, application of the principles of quantum mechanics is predicted to enable high-capacity communication and ultra-high-speed computers exceeding the limits of current technologies. One of the most important tasks for enabling such new applications is to establish the technology of quantum teleportation, which enables the transfer of quantum bits of information carried by photons from a sender to a receiver at a distance.

However, conventional quantum teleportation devices require a large optical table with hundreds of optical instruments and had reached the limits of scalability.

The photonic chip (lower left) contains the core circuits of quantum teleportation (upper), which conventionally requires a large optical table with hundreds of instruments (lower right). (Source: Furusawa Laboratory)

The photonic chip developed by the group contains an optical circuit microfabricated in glass on a silicon substrate measuring 26 millimeters by 4 millimeters, replacing the very large number of optical elements arranged over an area of about 1 m² for the generation and detection of quantum entanglement. The over 10,000 times reduction in size could resolve scalability issues in one fell swoop, helping enabling the realization of high-capacity quantum communication and ultra-high-speed quantum computers.

Measuring perovskite FETs

Researchers from Wake Forest University and the University of Utah successfully fabricated hybrid perovskite field-effect transistors and measured their electrical characteristics at room temperature.

“We designed the structure of these field-effect transistors that allowed us to achieve electrostatic gating of these materials and determine directly their electrical properties,” said Oana Jurchescu, an assistant professor of physics at Wake Forest. “Then we fabricated these transistors with the Utah team and we measured them here in our lab.”

Until now, researchers have not been able to fabricate field-effect transistors to measure the charge transport of the materials. Necessary prerequisites for a material that forms an efficient solar cell are strong optical absorption and efficient charge carrier transport, Jurchescu said. With these first generation transistors, the researchers were able to directly measure and calculate the electrical properties, eliminating indirect approximations.

“This work shows that in addition to solar cell technologies, the hybrid perovskites have potential to be used in a variety of optoelectronic applications,” said Zeev “Valy” Vardeny, professor of physics and astronomy at the University of Utah.

Hybrid perovskites have taken the solar cell field by storm since they were first introduced in 2009. The power conversion efficiencies have grown from around 4 percent to 20 percent in just five years. By comparison, other conventional materials used to generate electricity from sunlight have taken decades to achieve high performance levels.

“We will learn from these first lessons and try to make them better,” Jurchescu said. “Really, this is just the first step. Next we will look into the spin manipulation of the injected carriers in these devices and other electrical, optical and magnetic field applications.”

Nanowires team up with bacteria

Researchers at the University of California, Berkeley, say that by combining nanoscale materials with bacteria, they have opened the door to a new way of designing systems that could efficiently turn carbon dioxide, water, and sunlight into useful organic compounds—similar to what plants do through photosynthesis.

The new system is the first one in which semiconductors have been directly combined with bacteria for artificial photosynthesis, says Peidong Yang, a professor of chemistry and materials science UC Berkeley, and an inventor of the system. Previous similar systems have relied on bulky solar panels to provide renewable electricity. In this system, semiconducting nanowires capture energy from sunlight and pass electrons to electrotrophic bacteria nestled within the wires. The electrotrophs use the electrons to turn carbon dioxide and water into useful chemical building blocks. Those are then passed to genetically engineered E. coli, which in turn make a wide range of products.

Bacteria, nestled within an array of nanowires, use electricity from the wires to produce valuable chemicals. (Source: Peidong Yang/UC Berkley)

The researchers demonstrated that the system could make butanol, a polymer used in biodegradable plastics, and three pharmaceutical precursors. It could in principle be used to make many other products, including chemicals that are valuable in relatively small volumes.

The new system is about as efficient as natural photosynthesis at using the energy in sunlight, says Yang. That’s not enough for the process to be commercially viable, but he says new semiconductor materials his group is currently working with should make the process more competitive.