Researchers at the University of California, Santa Barbara have developed a chip-scale, ultra-low linewidth laser that matches or exceeds the performance of larger, more expensive desktop systems. Using rubidium atoms as a reference, the laser provides excellent stability and low noise, making it ideal for applications such as quantum computers, atomic clocks and portable quantum sensors. The research was published in Scientific Reports .
Lasers are the technology of choice for experiments that require extremely precise atomic measurement and control, such as two-photon atomic clocks, cold-atom interferometers, and quantum gates.
The more spectrally pure a laser is (the more it emits a single color or frequency), the better its quality. Currently, this stable, ultra-low-noise light is produced using traditional lab-scale laser technology, which relies on large, expensive benchtop systems designed to generate, collect and emit photons within a specific spectral range.
But what if these atomic applications extended beyond the lab and the laboratory bench? That’s a primary goal of Daniel Blumenthal’s lab at the University of California, Santa Barbara, where his team is working to replicate the performance of these lasers in a portable device that’s light and small enough to fit in your hand.
These compact lasers will enable scalable laser solutions for practical quantum systems as well as portable, field-deployable lasers for space-based quantum sensors, which will have implications in technology areas such as quantum computers with trapped neutral atoms and ions, and cold-atom quantum sensors such as atomic clocks and gravimeters .
Andrey Ishchenko, Graduate Research Fellow, University of California, Santa Barbara
As part of their work in this direction, Blumenthal, Ischenko and their colleagues have developed a chip-scale, ultra-low linewidth, self-injected 780 nm laser. The researchers say that this tiny device, about the size of a matchbox, could potentially outperform existing narrow-linewidth 780 nm lasers at a fraction of the cost and space required to manufacture them.
Lasso the tear laser
Key to the laser’s performance lies in the atom that powered its development: rubidium. Rubidium was chosen because it has well-established properties that make it ideal for many high-precision applications. The atom’s sensitivity makes it particularly useful in cold-atom physics and sensing, and its stable D2 optical transition makes it an excellent candidate for atomic clocks.
By irradiating a near-infrared laser onto a vapor of rubidium atoms, which serve as a reference atom, it is possible to obtain the characteristics of stable atomic transitions.
We can use atomic transition lines to bracket a laser beam, in other words, by locking the laser to an atomic transition, the laser will take on more or less the properties of that atomic transition in terms of stability .
Daniel Blumenthal, senior study author, University of California, Santa Barbara
But precision lasers are not just a light source: To achieve the desired light quality, “noise” must be minimized, which Blumenthal likens to the difference between a guitar string and a tuning fork.
If you use a tuning fork to produce the note C, it will probably be a perfect C. But if you strum a C on a guitar, you will hear other notes. These miniature lasers enable scalable laser solutions for practical quantum systems, as well as lasers for space-based quantum sensors that are portable and deployable in the field .
Daniel Blumenthal, senior study author, University of California, Santa Barbara
Lasers can use different frequencies (or “colors”) to create complementary “tones.” In desktop systems, additional components are added to further fine-tune the laser light to produce the single frequency required (in this case pure crimson light). The challenge for researchers is to integrate all these functions and capabilities onto a single chip.
To achieve this, the research team used the silicon nitride platform to create the world’s lowest-loss waveguides (developed in Blumenthal’s lab), commercially available Fabry-Perot laser diodes, and high-quality resonators with superior performance.
Their device outperforms previously reported desktop and integrated lasers by four orders of magnitude in key metrics such as frequency noise and linewidth. This breakthrough technology makes it possible to reproduce the performance of large, bulky systems in a much smaller form factor.
“The importance of low linewidth values is that they allow us to achieve compact lasers without sacrificing laser performance,” explains Ishchenko. ” In a sense, full chip-scale integration gives us better performance than conventional lasers. These linewidths also help us to better interact with the atomic system and eliminate the contribution of the laser noise to fully resolve the atomic signal depending on the environment we are sensing, for example .”
The low linewidth (record sub-Hz fundamental frequency and sub-KHz integral for this project) demonstrates the laser’s stability and its ability to filter both internal and external noise.
Other advantages of the technology include its affordability (it uses $50 diodes) and a scalable, cost-effective manufacturing process. The method is compatible with CMOS technology and was developed using a wafer-scale approach inspired by the field of electronic chip manufacturing.
If successful, the technology could lead to high-performance, highly accurate, low-cost optically integrated lasers that can be used for a wide range of applications both in and outside the laboratory, including quantum experiments, measuring atomic time, and detecting extremely small signals such as changes in gravitational acceleration around the Earth.
“If we put these instruments on satellites, we can make gravity maps of the Earth and its surroundings with a reasonable degree of accuracy,” Blumenthal said. By sensing the gravitational field around the Earth, we can measure things like sea level rise, changes in sea ice, and earthquakes .”
He also highlighted that the technology’s lightweight design, low power consumption and compact size make it “ideal” for deployment in space.
Other authors on the study include Andrew S. Hunter, Dabapam Bose, Nitesh Chauhan, Maiting Song, Kaikai Lu and Mark W. Harrington.
Journal References:
Isichenko, A., et al . (2024) Sub-kHz linewidth, sub-Hz fundamental-integrated injection-locked hybrid laser. Scientific Reports . Source: http://www.dept.gov/depts …
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University of California, Santa Barbara
