Researchers from the Swiss Federal Institute of Technology (EPFL) have announced the first ultrafast laser delivering 1.05 nanojoules of energy in extremely short pulses as short as 147 femtoseconds integrated onto a photonic chip.

The research team behind the accomplishment said that successfully scaling down ultrafast lasers of this magnitude from large tabletop models to microchip integration could enable extremely advanced sensing technologies, improve medical imaging, and potentially enable next-generation atomic clocks for yet-to-be-developed communication and navigation applications.

Ultrafast Lasers on a Microchip Scale Have Remained an Elusive Photonics ‘Holy Grail’

In a statement announcing the breakthrough, team leader and EPFL Professor Tobias J. Kippenberg explained that ultrafast lasers emit extremely short pulses of light energy lasting only a few hundred femtoseconds, which are quadrillionths of a second. Although the development of this category of lasers has enabled ultraprecise micromachining, atomic clocks, and advanced eye surgery, the team notes that the “bulky” technology has been limited to optical laser tables.

On the other end of the spectrum, engineers have built extremely small photonic chips that channel light in a similar way to how traditional microprocessors channel electricity to perform calculations. Some photonic chip designs are already widely used in the communications industry. However, integrating the ultrafast laser technology at the power levels demonstrated by the research team into a smaller chip has remained particularly elusive.

“For more than twenty years, a high-pulse-energy femtosecond laser on chip was widely regarded as a holy grail of integrated photonics,” Professor Kippenberg explained.

“Overlooked, Surprisingly Elegant Technology” Could Enable Futuristic Technologies

To find the nexus between size, speed, and power that could enable a true high-energy, ultrafast laser on a chip, the EPFL team opted to turn away from traditional laser designs and instead took advantage of what they termed a “largely overlooked” design: a Mamyshev oscillator.

Unlike some designs, this oscillator uses a nonlinear waveguide placed between the two optical filters in the laser cavity, each of which allows a different color of the spectrum to pass through. When a strong light pulse travels through the installed waveguide, the beam broadens into a wider range of colors.

The team notes that this effect allows part of the light pulse to pass through both filters and remain in circulation. However, they also note that “weak light” does not broaden enough when impacting the waveguide and is ‘rejected.’

Zheru Qiu, a co-lead author of the paper, said that beyond speed and power, their chip has commercial potential due to its material simplicity.

“This design is especially attractive because it does not require any component that is difficult to make on this erbium-doped silicon nitride chip,” Qiu explained.

Another advantage to the team’s design is its resistance to nonlinear interaction. Put simply, when waveguides squeeze light into tiny spaces, that same light interacts strongly with itself.

The resulting nonlinear interactions can degrade the performance of traditional photonic chip designs. However, Qiu said that a laser with a Mamyshev oscillator is “well suited to the tight confinement of light in photonic chips.”

“Our result shows that it is not only possible, but that it can be achieved with a surprisingly elegant architecture that the integrated-photonics community had overlooked,” Qiu explained of their revolutionary architecture. 

Integrated Chips Could Replace Large, Expensive Laboratory Lasers

When discussing the versatility of their ultrafast laser on a chip, the researchers noted that the prototype’s 42-cm-long laser cavity can be folded down to a size smaller than a matchhead. For comparison, they noted that 42 centimeters is “far smaller than optical fiber-based lasers.”

For potential commercial applications, the team said their chips can be manufactured “at-scale,” with an excess of 1,000 individual laser cavities per chip. Although currently in the demonstration phase, the team suggested that a fully realized commercial-grade ultrafast laser-on-a-chip could provide engineers with a critical microengineering tool they have lacked.

“With kilowatt-level peak powers, the chip can drive demanding applications that have long depended on large, expensive laboratory lasers,” says Qiu.

The researchers suggested their chip could impact several technologies, such as advanced sensing and medical imaging, and potentially pave the way for futuristic technologies based on ultraprecise atomic clocks.

The study “High-pulse-energy integrated mode-locked laser using a Mamyshev oscillator” was published in Nature.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

An international team of researchers has demonstrated a theoretical framework showing that state-of-the-art trapped-ion atomic clocks could be tuned to a sensitivity precise enough to measure the quantum superposition of time, in which different flows of time exist simultaneously at the quantum level.

The researchers behind the framework said the next step will be to prove their concept experimentally. If successful, they suggest that trapped-ion atomic clocks could potentially help unravel physics’ other fundamental question: the elusive nature of gravity.

Quantum Superposition, Gravity, Atomic Clocks, Albert Einstein, and the Flow of Time

In the macro world, time moves in one direction. Although famed 20th-century scientist Albert Einstein showed that gravity and speed can alter the rate at which time flows, his theory of relativity conceded that time at the macro scale inexorably flows in a forward direction.

As recently reported by The Debrief, the research team behind the new theoretical framework notes that this arrow of time remains poorly understood, leading to several theories attempting to explain how it actually works. For scientists studying behavior at the quantum scale, the movement of time becomes even more complex. That’s because time can exist in superposition, a state where different flows of time all exist at the same moment. However, the team notes, this “interplay of time” between relativity and quantum physics has not yet been experimentally verified.

Curious if new, state-of-the-art trapped-ion atomic clocks were precise enough to measure the quantum superposition of time to quantify different flows of time occurring at the same moment, researchers from Kyushu University, in collaboration with the Stevens Institute of Technology, University of Waterloo, the National Institute of Standards and Technology, Colorado State University, and Stockholm University, explored a theoretical framework capable pf capturing this elusive phenomenon.

Theoretical Framework Improves Sensitivity ‘By 100 to 1000 Times’

According to a statement announcing a potential breakthrough in measuring the quantum superposition of time, atomic clocks work by monitoring the frequency of certain atoms. This fundamental design enabled unprecedented timekeeping accuracy, with applications in satellite navigation and GPS systems.

The team notes that state-of-the-art trapped-ion configurations of atomic clocks are so precise and sensitive that “they can detect the time dilation predicted by Einstein’s theory over a height difference of a few millimeters.”

Associate Professor Joshua Foo of Kyushu University’s Institute for Advanced Studies, and one of the lead authors of the paper detailing the measurement framework, said it is the precision of these cutting-edge instruments that motivated his team to design their theoretical model.

“We found that the atomic clock’s motion becomes ‘entangled’ with its internal energy,” Professor Foo explained. “The signature of this entanglement is that the clock itself loses some of its quantum properties, which can be detected using modern techniques.”

When Foo and colleagues introduced a new technique for controlling the motion of these advanced atomic clocks, the professor said their framework indicates an improvement in sensitivity to this effect “by 100 to 1000 times.”

Experimental Proof and Probing the Nature of Gravity

When discussing the possible impact of their new theoretical framework, should it ultimately be used to quantify the quantum superposition of time, the researchers noted that it established atomic clocks as a viable tool for exploring several phenomena in the quantum world that had previously proven difficult to measure accurately, including the quantum nature of time. They also note that it “opens a new experimental frontier in fundamental physics,” as well as offering a viable path to more precise, next-generation atomic clocks.

Next, Foo said that the team is developing a detailed real-world experiment “bringing our theoretical model to reality.” If successful, these upcoming efforts will provide further insights into their model that do not appear in the theoretical version. The research also said his team is interested in whether atomic clocks based on their model could be used to probe the quantum realm of gravity, which he calls “the other fundamental question in physics.”

The study “Quantum Signatures of Proper Time in Optical Ion Clocks” was published in Physical Review Letters.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.