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

For experiments that require ultra-precise measurements and control of atoms (think two-photon atomic clocks, cold-atom interferometric sensors, and quantum gates), lasers are the technology of choice because they are more spectrally pure (emitting a single color/frequency). better. Conventional laboratory-scale laser technology currently achieves this stable, ultra-low-noise light via bulky and expensive benchtop systems designed to generate, harness, and emit photons in a narrow spectral range.

But what if these atomic applications could go beyond their current limits in laboratories and on benches? This advance is at the heart of efforts in UC Santa Barbara engineering professor Daniel Blumenthal’s lab, where his team seeks to recreate the performance of these lasers on lightweight devices that can fit in the palm of your hand.

“These smaller lasers will enable the creation of scalable laser solutions for real-world quantum systems, as well as lasers for wearable, field-deployable, and space-based quantum sensors,” said Andrei Isichenko, a graduate student researcher at the Blumenthal laboratory. “This will impact technology areas such as quantum computing with neutral atoms and trapped ions as well as cold-atom quantum sensors such as atomic clocks and gravimeters. »

In a newspaper article Scientific reportsBlumenthal, Isichenko and their team present a development in this direction with a very narrow linewidth self-injection-locked 780 nm laser at chip scale. The matchbox-sized device can outperform current narrow-linewidth 780-nm lasers, researchers say, at a fraction of the manufacturing cost and space needed to contain them.

Lasso the laser

The atom behind the laser’s development is rubidium, so chosen because of its well-known properties that make it ideal for a variety of high-precision applications. The stability of its D2 optical transition lends the atom well to atomic clocks; the sensitivity of the atom also makes it a popular choice for sensors and cold atom physics. By passing a laser through a vapor of rubidium atoms as an atomic reference, a near-infrared laser can acquire the characteristics of a stable atomic transition.

“You can use the atomic transition lines to lasso the laser,” noted Blumenthal, the lead author of the paper. “In other words, by locking the laser onto the atomic transition line, the laser more or less adopts the characteristics of that atomic transition in terms of stability.”

But a sophisticated red light does not produce a precision laser. For light of the desired quality, “noise” must be eliminated. Blumenthal describes this as a tuning fork compared to guitar strings.

“If you have a tuning fork and you hit a C note, it’s probably a pretty perfect C,” he explained. “But if you strum a C on a guitar, you can hear other sounds there.” Likewise, lasers can incorporate different frequencies (colors) that generate additional “tones.”

To create the desired unique frequency – pure dark red light in this case – tabletop systems incorporate additional components to further calm the laser light. The challenge for the researchers was to integrate all these features and performances on a chip.

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

“The importance of low linewidth values ​​is that we can achieve a compact laser without sacrificing laser performance,” explained Isichenko.

“In some ways, performance is improved over conventional lasers through full chip-scale integration. These linewidths help us better interact with atomic systems, eliminating contributions from laser noise to completely resolve the atomic signal in response, for example, to the environment they sense. Low linewidths (in the context of this project, a fundamental below Hz record and an integral below KHz) are. revealing of the stability of laser technology and its ability to overcome noise from external and internal sources.

Other advantages of this technology include cost: it uses a $50 diode and employs a cost-effective and scalable manufacturing process created using a CMOS-compatible wafer-scale process that draws inspiration from world of electronic chip manufacturing.

The success of this technology means that it will be possible to deploy these high-performance, precision, low-cost integrated photonic lasers in a variety of situations inside and outside the laboratory, including quantum experiments, timekeeping atomic and detection of the lowest intensity. of signals, such as changes in gravitational acceleration around the Earth.

“You can place them on satellites to create a gravitational map of the Earth and its environment with some precision,” Blumenthal said. “You could measure sea level rise, changes in sea ice and earthquakes by detecting gravitational fields around Earth.” The compactness, low power consumption and light weight are a “perfect fit,” he added, for the technology to be deployed in space.