Portable, Ultra-Precise Laser Technology for Quantum Systems

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Lasers are essential for experiments requiring extremely precise measurements and atom-level control, such as those used in two-photon atomic clocks, cold-atom interferometer sensors, and quantum gates. Currently, these applications rely on large, expensive, and stationary tabletop laser systems that produce stable, spectrally pure light. But what if these technologies could be miniaturized and made portable? This is the goal of UC Santa Barbara engineering professor Daniel Blumenthal’s lab, where his team is working to develop small, lightweight lasers with the same performance as current lab-based systems.

"These smaller lasers will enable scalable solutions for quantum systems, as well as portable and field-deployable quantum sensors for space," said Andrei Isichenko, a graduate student researcher in Blumenthal's lab. "This could revolutionize quantum computing with neutral atoms, trapped ions, and quantum sensors like atomic clocks and gravimeters."

In a recent paper published in Scientific Reports, Blumenthal, Isichenko, and their team presented a new chip-scale ultra-low-linewidth self-injection locked 780 nm laser. This compact device, roughly the size of a matchbox, outperforms current narrow-linewidth 780 nm lasers and can be manufactured at a fraction of the cost and space requirements.




The key atom behind this development is rubidium, chosen for its stability and sensitivity. These properties make rubidium ideal for high-precision applications such as atomic clocks and quantum sensors. By passing a laser through rubidium vapor, the laser takes on the characteristics of rubidium's stable atomic transition, ensuring a more reliable and stable light source.

"You can use the atomic transition lines to 'lasso' the laser," said Blumenthal. "By locking the laser to the atomic transition line, it adopts the stability of that atomic transition."

To achieve this precision, the team needed to reduce noise, or unwanted variations in the laser's frequency. Blumenthal compares the task to tuning a guitar: while a tuning fork produces a pure note, a guitar string produces extra tones. The researchers used a combination of a commercially available Fabry-Perot laser diode, low-loss waveguides, and high-quality resonators on a silicon nitride platform to integrate all necessary components onto a chip. Their device achieved performance that surpasses some traditional tabletop lasers, reducing frequency noise and linewidth by four orders of magnitude.
 
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