Tabletop precision Lasers for Quantum Science

“These smaller lasers will enable scalable laser solutions for actual quantum systems, as well as lasers for portable, field-deployable and space-based quantum sensors”

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

But what if these atomic applications could be lifted from their current confines in labs and on benchtops? This advancement is at the heart of the effort at 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 scalable laser solutions for actual quantum systems, as well as lasers for portable, field-deployable and space-based quantum sensors,” said Andrei Isichenko, a graduate student researcher in Blumenthal’s lab. “This will impact technology spaces such as quantum computing with neutral atoms and trapped ions and also cold atom quantum sensors such as atomic clocks and gravimeters.”  

In a paper in the journal Scientific Reports, Blumenthal, Isichenko and team present a development in this direction with a chip-scale ultra-low-linewidth self-injection locked 780 nm laser. This roughly matchbox-sized device, say the researchers, can perform better than current, narrow-linewidth 780 nm lasers, for a fraction of the cost to manufacture, and the space to hold them.

Lassoing the Laser

The atom motivating the laser  development is rubidium, so chosen because of 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 atom’s sensitivity also makes it a popular choice for sensors and cold atom physics. By passing a laser through a vapor of rubidium atoms as the atomic reference, a near infrared laser can take on the characteristic of the stable atomic transition.

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

But a fancy red light does not a precision laser make. For a light of the desired quality, “noise” must be removed. Blumenthal describes this as a tuning fork versus guitar strings.

“If you have a tuning fork and 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 tones in there.”  Similarly, lasers may incorporate different frequencies (colors) that generate extra “tones.” To create the desired single frequency  — pure deep-red light in this case — tabletop systems incorporate additional components to further calm down the laser light. The challenge for the researchers was to integrate all that functionality and performance onto a chip.