Microfrequency waveforms are specialized light sources that can function as clocks, rulers, and light-based sensors to measure time, distance, and molecular composition with great precision. Stanford’s new research presents a new tool to study the quantum characteristics of these sources.
By Taylor Kubota
Unlike the jumble of frequencies produced by the light that surrounds us in everyday life, each frequency of light in a specialized light source known as the ‘soliton’ frequency comb oscillates in unison, generating solitary pulses with synchronization. consistent.
Each “tooth” of the comb is a different color of light, spaced so precisely that this system is used to measure all kinds of phenomena and characteristics. The miniaturized versions of these combs – called micropines – currently in development have the potential to improve countless technologies, including GPS systems, telecommunications, autonomous vehicles, greenhouse gas monitoring, machine autonomy. space and ultra-precise timing.
The laboratory of Stanford University electrical engineer Jelena Vučković has only recently joined the microcomb community. “Many groups have demonstrated on-chip frequency combs in a variety of materials, including recently silicon carbide by our team. However, until now, the quantum optical properties of frequency combs have been elusive, ”said Vučković, Jensen Huang global leadership professor at the School of Engineering and professor of electrical engineering at Stanford. “We wanted to take advantage of our group’s quantum optics experiment to study the quantum properties of the soliton microtext. “
While soliton micropins have been made in other labs, Stanford researchers are among the first to study the system’s quantum optical properties, using a process they describe in a Dec. 16 paper published in Nature Photonics. . When created in pairs, micropine solitons are believed to exhibit entanglement – a relationship between particles that allows them to influence each other even at incredible distances, which underpins our understanding of quantum physics and constitutes the basis of all proposed quantum technologies. Most of the “classic” light that we encounter on a daily basis is not tangled.
“This is one of the first demonstrations that this miniaturized frequency comb can generate interesting quantum light – unclassical light – on a chip,” said Kiyoul Yang, a researcher at Vučković’s Nanoscale and Quantum Photonics Laboratory and co. -author of the article. . “This may open a new avenue for broader explorations of quantum light using the frequency comb and photonic integrated circuits for large-scale experiments.”
Proving the usefulness of their tool, the researchers also provided compelling evidence for quantum entanglement within the soliton micropine, which has been theorized and speculated but has not yet been proven by existing studies.
“I would really like solitons to become useful for quantum computing, because it is a very well studied system,” said Melissa Guidry, graduate student at the Nanoscale and Quantum Photonics Lab and co-author of the article. “We have a lot of technology at this point to generate solitons on low power chips, so it would be exciting to be able to take that and show you have a tangle.”
Between the teeth
Former Stanford physics professor Theodor W. Hänsch won the Nobel Prize in 2005 for his work on the development of the first frequency comb. To create what Hänsch studied requires complicated equipment the size of a table. Instead, these researchers chose to focus on the new “micro” version, where all parts of the system are integrated into a single device and designed to fit on a microchip. This design saves on cost, size and energy.
To create their miniature comb, the researchers pump laser light through a microscopic silicon carbide ring (which was painstakingly designed and fabricated using resources from shared Stanford Nano facilities and Stanford nanofabrication facilities) . As it travels through the ring, the laser increases in intensity and, if all goes well, a soliton is born.
“It’s fascinating that instead of having this fancy, complicated machine, you could just take a laser pump and a very small circle and produce the same type of specialized light,” said Daniil Lukin, a graduate student at Nanoscale. and Quantum Photonics Lab. and co-author of the article. He added that the generation of the micro-tag on a chip allows for wide spacing between the teeth, which was a step towards being able to see the finer details of the comb.
The next steps involved equipment capable of detecting individual particles of light and lining the micro-ring with multiple solitons, thereby creating a soliton crystal. “With the soliton crystal, you can see that there are actually smaller pulses of light between the teeth, which we are measuring to infer the entanglement structure,” Guidry explained. “If you park your detectors there, you can get a good look at the interesting quantum behavior without drowning it with the coherent light that makes up the teeth. “
Seeing that they were doing some of the earliest experimental studies on the quantum aspects of this system, the researchers decided to try to confirm a theoretical model, called a linearized model, which is commonly used as a shorthand for describing complex quantum systems. When they made the comparison, they were amazed to find that the experiment matched the theory very well. So, although they have not yet directly measured that their microtag exhibits quantum entanglement, they have shown that its performance corresponds to a theory that involves entanglement.
“The take-home message is that this opens the door for theorists to do more theory because now, with this system, it is possible to experimentally verify this work,” Lukin said.
Proving and using quantum entanglement
Microcombs in data centers could increase the speed of data transfer; in satellites, they could provide more accurate GPS or analyze the chemical composition of distant objects. Vučković’s team is particularly interested in the potential of solitons in certain types of quantum computing, as solitons should be strongly entangled as soon as they are generated.
With their platform and the ability to study it from a quantum perspective, researchers at the Nanoscale and Quantum Photonics Lab are keeping an open mind about what they might do next. Near the top of their list of ideas is the opportunity to perform measurements on their system that definitively prove quantum entanglement.
The research was funded by the Defense Advanced Research Projects Agency under the PIPES and LUMOS programs, an Albion Hewlett Stanford (SGF) Graduate Fellowship, an NSF Graduate Research Fellowship, Fong SGF and the graduate scholarship in science and engineering of national defense.
Rahul Trivedi, formerly at Stanford University and now at the Max-Planck-Institute for Quantum Optics in Germany, is also a co-author. Vučković is also a member of the Ginzton Lab, Stanford Bio-X, the Wu Tsai Neurosciences Institute, and the PULSE and SIMES institutes.