Research Bits: June 27

Tunable soliton microcomb

Researchers from the University of Rochester and CalTech say they have created the first microwave-rate soliton microcomb that can control the repetition rate at a high speed. Microcombs are frequency combs that can fit on a microchip, which will be useful in photonics. Solitons are solitary waves that keep their shape as they move at a constant speed. The team put an electro-optic modulation element into a lithium niobate comb microresonator, according to their journal article. A lithium niobate resonator was able to tune the bandwidth and frequency modulation rates of a microwave source to a modulation bandwidth up to 75 MHz and a continuous frequency modulation rate up to 5.0 × 1014 Hz/s.

“Nonlinear integrated photonics is trying to produce this kind of a frequency comb on a chip-scale device,” says Qiang Lin, professor of electrical and computer engineering and optics at University of Rochester.

“The device provides a new approach to electro-optic processing of coherent microwaves and opens up a great avenue towards high-speed control of soliton comb lines that is crucial for many applications including frequency metrology, frequency synthesis, radar/lidar, sensing, and communication,” says Yang He, the lead author, a postdoctoral scholar in Lin’s lab.

The National Science Foundation, Defense Threat Reduction Agency, and DARPA are supporting some of the research.

Yang He, Raymond Lopez-Rios, Usman A. Javid, Jingwei Ling, Mingxiao Li, Shixin Xue, Kerry Vahala, Qiang Lin. High-speed tunable microwave-rate soliton microcomb. Nature Communications, 2023; 14 (1) DOI: 10.1038/s41467-023-39229-3

Quantum toggle switch

A team of scientists from National Institute of Standards and Technology (NIST), University of Massachusetts Lowell, University of Colorado Boulder, and Raytheon BBN Technologies have created a programmable toggle-switch device for quantum computing that can toggle among three states. Two qubits are used in a cavity — the toggle can put the qubits together (for calculation), separate them, or connect them to a reader. The “readout resonator” circuit can read the output of the qubits’ calculations. The team was able to cut some of the noise by adjusting the strength of the connection between the qubits and the resonator.

Fig 1: This image shows the central working region of the device. In the lower section, the three large rectangles (light blue) represent the two quantum bits, or qubits, at right and left and the resonator in the center. In the upper, magnified section, driving microwaves through the antenna (large dark-blue rectangle at bottom) induces a magnetic field in the SQUID loop (smaller white square at center, whose sides are about 20 micrometers long). The magnetic field activates the toggle switch. The microwaves’ frequency and magnitude determine the switch’s position and strength of connection among the qubits and resonator.

Source: NIST (Credit: K. Cicak & R. Simmonds/NIST)

Noh, T., Xiao, Z., Jin, X.Y. et al. Strong parametric dispersive shifts in a statically decoupled two-qubit cavity QED system. Nat. Phys. (2023). https://doi.org/10.1038/s41567-023-02107-2

Source-gated transistors temp issue

The emerging semiconductor material called indium-gallium-zinc oxide (IGZO) may be the key to solving — or at least chipping away at — the problem with high temperature dependence of the drain current (TDDC) in source-gated transistors (SGTs). One result could be an energy efficient, low-cost flexible displays. A team from University of Surrey is using amorphous In 2 Ga 2 ZnO 7 (IGZO) tunnel-contact SGTs (TC-SGTs) and a nanoscale contact engineering technique to improve the temperature stability of SGTs.

Alfarisyi et al., “Evidence of Improved Thermal Stability via Nanoscale Contact Engineering in IGZO Source-Gated Thin-Film Transistors,” in IEEE Transactions on Electron Devices, doi: 10.1109/TED.2023.3276337.