Power/Performance Bits: Oct. 20

Benchmarking quantum layout synthesis
Computer scientists at the University of California Los Angeles found that current compilers for quantum computers are inhibiting optimal performance and argue that better quantum compilation design could help improve computation speeds up to 45 times.

The team designed a family of benchmark quantum circuits with known optimal depths or sizes, which could be used to improve quantum layout synthesis tools. They tested their benchmarks in four of the most used quantum compilation tools.

“We believe in the ‘measure, then improve’ methodology,” said Jason Cong, a professor of computer science at UCLA Samueli School of Engineering. “Now that we have revealed the large optimality gap, we are on the way to develop better quantum compilation tools, and we hope the entire quantum research community will as well.”

Cong noted that better layout synthesis could halve quantum circuit depth, which would effectively double the length of time before quantum devices become decoherent, losing the information encoded in them.

“This compilation research could effectively extend that time, and it would be the equivalent to a huge advancement in experimental physics and electrical engineering,” Cong added. “So we expect these benchmarks to motivate both academia and the industry to develop better layout synthesis tools, which in turn will help drive advances in quantum computing.”

The benchmarks, named QUEKO, are open source and available on GitHub.

Tiny electro-optical modulator
Engineers at the University of Rochester built a tiny electro-optical modulator for controlling the movement of light through photonics-based chips. The team used a thin film of lithium niobate (LN) bonded on a silicon dioxide layer to create what they say is the smallest LN modulator yet, that also operates at high speed and is energy efficient.

This “paves a crucial foundation for realizing large-scale LN photonic integrated circuits that are of immense importance for broad applications in data communication, microwave photonics, and quantum photonics,” said Mingxiao Li, a graduate student at Rochester.

A schematic drawing shows an electro-optical modulator developed in the lab of Qiang Lin, professor of electrical and computer engineering. The smallest such component yet developed, it takes advantage of lithium niobate, a “workhorse” material used by researchers to create advanced photonics integrated circuits. (Source: University of Rochester illustration / Michael Osadciw)

Due to its electro-optic and nonlinear optic properties, lithium niobate has “become a workhorse material system for photonics research and development,” said Qiang Lin, professor of electrical and computer engineering at Rochester. “However current LN photonic devices, made upon either bulk crystal or thin-film platform require large dimensions and are difficult to scale down in size, which limits the modulation efficiency, energy consumption, and the degree of circuit integration. A major challenge lies in making high-quality nanoscopic photonic structures with high precision.”

Previously, the lab used lithium niobate to create a photonic nanocavity that can tune wavelengths using only two to three photons at room temperature. The team says the nanocavity can be used in conjunction with the new modulator in creating a nanoscale photonic chip.

Origami mechanical switch
Researchers from the New York University Abu Dhabi and University of Warwick propose a way to create mechanical binary switches out of origami. Using the origami Kresling pattern, the team built multiple mechanical switches which when combined served as a functioning mechanical memory board.

The Kresling pattern is an example of nonrigid origami, in which the panels between folds can deform. Folding a piece of paper using this pattern generates a bellowslike structure that can flip between one orientation and another. The bellows act as a type of spring and can be controlled by vibrating a platform that holds the bellows. This creates a switch, which the investigators refer to as a Kresling-inspired mechanical switch, or KIMS.

Oscillating a platform holding the KIMS up and down at a certain speed will cause it to switch between its two stable states. The researchers used an electrodynamic shaker to provide controlled movements of the base and monitored the upper surface of the KIMS using a laser. In this way, they were able to map out and analyze the basic physics that underlies the switching behavior.

“We used the Kresling origami pattern to also develop a cluster of mechanical binary switches,” said Ravindra Masana, a research scientist at NYU Abu Dhabi. “These can be forced to transition between two different static states using a single controlled input in the form of a harmonic excitation applied at the base of the switch.”

The group built a 2-bit memory board created by placing two KIMS units on a single platform. Because each KIMS bit has two stable states, four distinct states identified as S00, S01, S10 and S11 can be obtained. Oscillations of the platform will cause switching between these four stable states. The team says the proof of concept could be extended to multiple KIMS units, creating a type of mechanical memory.

“Such switches can be miniaturized,” said Mohammed Daqaq, director of the Laboratory of Applied Nonlinear Dynamics at NYU Abu Dhabi. “Instead of using a bulky electrodynamic shaker for actuation, the memory board can then be actuated using scalable piezoelectric and graphene actuators.”