Bringing the power of tabletop precision lasers for quantum science to the chip scale

For experiments that require ultra-high precision measurements and control of atoms (think two-photon atomic clocks, cold atom interferometer sensors, quantum gates), more spectrally pure (emitting a single color/frequency ) laser is the technology of choice. Better. Traditional laboratory-scale laser technology currently achieves this ultra-low noise, stable light through large, expensive benchtop systems designed to generate, utilize, and emit photons within a narrow spectral range. I am.

But what if we could free these atomic applications from their current limitations in the lab or on the benchtop? This advance is at the heart of the work in the lab of University of California, Santa Barbara, engineering professor Daniel Blumenthal, whose The team aims to replicate the performance of these lasers in a lightweight device that fits in the palm of your hand.

“These smaller lasers enable scalable laser solutions for real-world quantum systems, as well as lasers for portable and field-deployable space-based quantum sensors,” Blumenthal said. said Andrei Ishchenko, a graduate student researcher in the lab of . “This will have implications for technological fields such as quantum computing using neutral atoms and trapped ions, as well as cold atom quantum sensors such as atomic clocks and gravimeters.”

In a paper published in Scientific Reports, Blumenthal, Isichenko and their team present developments in this direction with a chip-scale ultra-low linewidth self-injected locking 780 nm laser. The researchers say the nearly matchbox-sized device can outperform current narrow-linewidth 780-nm lasers at a fraction of the cost to manufacture and the space to maintain it.

lasso the laser

The atom that drove laser development was rubidium, chosen for its well-known properties that make it ideal for a variety of high-precision applications. The stability of the D2 optical transition makes atoms suitable for atomic clocks. Their atomic sensitivity also makes them popular for sensors and cold atomic physics. Near-infrared lasers can obtain stable atomic transition characteristics by passing the laser through the vapor of rubidium atoms, which serve as an atomic reference.

“You can use atomic transition lines to lasso a laser,” said Blumenthal, senior author of the paper. “In other words, by locking the laser to an atomic transition line, the laser more or less takes on the properties of that atomic transition in terms of stability.”

But the flashy red light isn’t created by a precision laser. To obtain the desired quality of light, the “noise” must be removed. Blumenthal describes it as being like a tuning fork and a guitar string.

“If you take a tuning fork and hit a C, it’s probably a pretty perfect C,” he explained. “But when you strum a C on your guitar, you hear other notes.” Similarly, lasers may incorporate different frequencies (colors) that produce additional “tones.”

To produce the desired single frequency (in this case, pure deep red light), the tabletop system incorporates additional components to further quieten the laser light. The researchers’ challenge was to integrate all the functionality and performance on a chip.

The researchers used a commercially available Fabry-Perot laser diode in combination with some of the world’s lowest-loss waveguides (manufactured in Blumenthal’s lab). Like the highest quality factor resonators, all manufactured on a silicon nitride platform. In doing so, they were able to replicate the performance of bulky tabletop systems. And, according to their tests, their device can outperform some tabletop lasers and previously reported integrated lasers by four orders of magnitude in important metrics such as frequency noise. I did. and line width.

“The importance of low linewidth values ​​is that they allow for compact lasers without sacrificing laser performance,” Ishchenko explained.

“Full chip-scale integration in some ways improves performance compared to traditional lasers. These linewidths help improve interaction with atomic systems and eliminate the effects of laser noise. for example, to completely resolve atomic signals in response to the environment they are sensing.” Linewidths are narrow (for this project, at sub-Hz base). Waves and sub KHz Integral) demonstrates the stability of the laser technology and its ability to overcome noise from both external and internal sources.

Additional advantages of this technology include cost. It uses a cost-effective and scalable manufacturing process created using $50 diodes and a CMOS-compatible wafer-scale process inspired by the world of electronic chip manufacturing.

The success of this technology means that these high-performance, high-precision, low-cost photonics-integrated lasers can be deployed in a variety of situations inside and outside the laboratory, including quantum experiments, atomic timing, and ultrafine particle sensing. . Signals such as changes in gravitational acceleration around the Earth.

“You can put these on a satellite and create a gravity map of the Earth and its surroundings with some degree of accuracy,” Blumenthal said. “By sensing the gravitational field around the Earth, we will be able to measure sea level rise, sea ice changes, and earthquakes.” Compactness, low power consumption, and light weight are “perfectly suited” for technology deployed in space. Then he added: