© Fraunhofer IOF

Photonics for the second quantum revolution

Lasers and other photonic systems are enablers of the second quantum revolution. Leading suppliers report enormous increases in demand.

Before Professor Theodor W. Hänsch was awarded the Nobel Prize in Physics in 2005 for his work in high-precision laser spectroscopy and optical frequency comb technology, the former director of the Max Planck Institute for Quantum Optics was one of the founders of Menlo Systems GmbH. The company now has more than 100 employees and, with its range of optical frequency combs and quantum laser systems, is a global leader in the future market for quantum technologies. According to Dr. Benjamin Sprenger, an expert for quantum technology and metrology at Menlo Systems, the company’s photonic solutions are currently used on six continents and in all four pillars of the market of the future. “We have customers in quantum communication, quantum simulation, quantum computing and quantum sensors and see great market opportunities for photonic solutions in each of these four areas,” he explains.

In the first quantum revolution, the use of quantum-mechanical processes paved the way for lasers, computer chips, transistors, and other semiconductor technologies and for modern medical and communications technology, a growing understanding and the increasingly precise control possibilities of photonic solutions is now triggering the second quantum revolution. With lasers, it is possible to control quantum effects rather than just using them. Lasers can cool atoms and ions almost to absolute zero (0 Kelvin or -273.15 °C), and, with laser light, they can be captured, moved and positioned. Also based on laser technology, high resolution laser spectroscopy and the aforementioned optical frequency combs enable ultra-precise frequency and distance measurement and determination of proton radii in the nucleus.

Photonic enablers of the second quantum revolution

In short: As enabling technologies, laser systems provide the necessary precision to make quantum states controllable and, as a consequence, usable for computing, simulation, communication and sensors. But according to Sprenger, to do this they must meet high requirements. “For example, laser systems for quantum computing must be extremely low-noise—and, ideally, all the necessary lasers, each tuned to the particular atomic transitions, should reach the experiment via fiber optics,” he explains. This is still a challenge, especially in the ultraviolet range and requires new developments and improvements in the solutions that are currently available. As in other areas of application, with the complex laser systems used in quantum technologies, it is important to guarantee robust 24/7 operation.

Companies such as Menlo Systems, TOPTICA AG and its subsidiary TOPTICA eagleyard as well as Berlin-based PicoQuant GmbH have their roots in well-known research institutes; they have been in the market for around 25 years and have now grown to the extent that they employ hundreds of highly qualified people. Because their solutions are in high demand throughout the world to drive quantum optical research and development, their dynamic growth in terms of sales and employees looks likely to continue. Dozens of jobs vacancies are witness to the positive development. The new exhibition area “World of QUANTUM” at LASER World of PHOTONICS (April 26-29, 2022) will offer interested users and applicants the opportunity to meet these and other leading players in the field of quantum technology. “We will be showing our latest developments and products in Munich,” promises Menlo expert Sprenger.

Spin-offs and startups are driving quantum technologies forward

Since it was established in 2011, MuQuans (µQuans), a spin-off from the Institut d’Optique d’Aquitaine in Bordeaux, has grown to become an important pioneer in quantum technology applications. Italian geophysicists use its Absolute Quantum Gravimeter for extensive gravitational measurements of the active volcano Mount Etna. Lasers from µQuans are also used by partner company Pasqal, which is developing a photonic approach for quantum computing that has been widely recognized worldwide. The aim is to develop a quantum platform that can carry out quantum simulations and calculations. To do this, Pasqal is using quantum manipulation of Rydberg atoms with laser light. According to µQuans founder Bruno Desruelle, the partners are adapting the laser technologies installed in the quantum gravimeter to suit the specific requirements of the Pasqal platform. “This will allow them to access systems that were validated for quantum technologies under operating conditions and that have proved unique performance, robustness, and reliability,” he emphasizes.

Desruelle is convinced of the potential of photonic solutions for quantum technologies. “Lasers can play a key role in various areas, as they enable highly efficient manipulation of quantum objects. This includes quantum sensors with gravimeters or inertial sensors, time and frequency measurement with atomic clocks, or in the areas of quantum communication and quantum information processing,” he explains. Especially in the last-mentioned applications, lasers are the enabler technology in almost all the approaches under consideration, no matter whether they are based on ions, Rydberg atoms, or trapped photons. This drives demand for quantum-specific laser systems and optical solutions. “We are seeing a lot of activity—in science, with a wealth of exciting research projects, and in the growing quantum industry, which is being driven by dynamic startups,” he says.

Young technology from young companies

One of these startups is Quantum Optics Jena (QUJ), a spin-off from the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) which is also located in Jena. Its founders, Dr. Oliver de Vries and Dr. Kevin Füchsel, worked on various research projects at the IOF and now press ahead with their product development. The first product is a miniaturized entangled photon source: Entanglement, which Einstein once described as “spooky”, describes the connection of the quantum-mechanical state of a pair of particles that remains even if the particles are separated by a large distance. The founder team is focusing on quantum computers, quantum communication, and quantum sensors and imaging.

“Initially, our priority is quantum communication, because we expect to see the first market-ready applications in this area,” explains Füchsel. With entangled photons, QUJ implements systems for quantum key distribution (QKD), with which communication via fiber optic of laser in space is to be secured. The company’s solution generates several million entangled photon pairs per second, which are exactly assignable thanks to today's nano-second precise resolution and high-precision polarization measurements. The founders are also developing solutions for this. “We are also implementing software to enable information processing, from detection of quantum states to using the generated key material,” he says.

In the fields of fiber-supported communication and laser-based data transfer from satellites to Earth, teams of scientists around the world are working towards making quantum technologies useful for absolutely secure, reliable optical communication. Although it may sound like science fiction, it is amazingly real. Scientists are examining issues such as how dust and clouds affect communication, how large the receiving telescopes on Earth and in space should be optimally, and how reliable transmission of the quantum keys will be across dozens of kilometers in the orbit or across hundreds and thousands of kilometers in space. One thing is already clear: The path towards finding practical answers will be through using lasers and other photonic technologies.