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The addition of the exhibition area World of QUANTUM, LASER World of PHOTONICS will bring together the most important scientific and industrial players in quantum technologies from April 26 to 29, 2022. We address this cooperation of industry and science in an interview. Immanuel Bloch, professor for experimental physics at LMU Munich, director at the Max Planck Institute for Quantum Optics in Garching and one of the spokespersons for the excellence cluster, the Munich Center for Quantum Science and Technology (MCQST), discusses with Dr. Thomas Renner, CEO of TOPTICA Photonics AG, which lasers and photonic solutions for quantum technology applications are currently in demand and what developments we can expect to see in the future.

Dr. Thomas Renner
© © TOPTICA Photonics AG
Dr. Thomas Renner, CEO of TOPTICA Photonics AG
Dr. Thomas Renner

Professor Bloch, a quick question beforehand: What is the Munich excellence cluster? Is the focus on basic research or specific applications?

Professor Immanuel Bloch: The cluster focuses more on basic research. But in Munich we also have the Munich Quantum Valley, where the focus is on application-related technology development. Both initiatives are interlinked. And in the region, the whole spectrum of quantum computing and simulation is covered, from quantum communication to applications in metrology and sensors. Education is an important pillar in the MCQST. For example, we have established a master’s course in the field of quantum sciences and technologies, which is extremely popular. This year alone we had 300 international applications, of which we admitted about 100. The industry is crying out for graduates to meet the many challenges of this industry of the future.

Dr. Thomas Renner: I can confirm that. We currently have 60 vacancies.

Dr. Renner, at the moment, the second quantum revolution takes place in scientific spheres. But, even so, to what extent is it an interesting market for TOPTICA?

Renner: We also split this field into basic research and application. Our roots are in science. TOPTICA was established almost 25 years ago as a scientific spin-off and still has very close connections to research. Sixty of our 400 employees have a doctor’s degree in quantum physics and quantum optics and contribute their knowledge not only in research and development but also in sales, applications, product management and production. When implementing laser systems and other photonic solutions, we get stimuli from research, which benefits us in all other user industries. This is because in science, the demands for precision and stability are extremely high. If you succeed here from a technological aspect, you will benefit from this in all other areas. Now quantum technology is ready to make the leap from basic research to industrial application. As a result, there are new demands with regard to the design and size of the systems, price levels and usability. In this respect, it benefits us that we have been delivering about 50 percent of our lasers to industrial customers for many years.

Could you describe some of the upcoming changes in more detail?

Renner: Quantum applications—such as quantum computers—are relatively well understood in science. But these days, a qubit needs up to a dozen lasers with different wavelengths that are not among the classic standard wavelengths such as 633 or 1064 nm. These lasers must also meet the highest demands in terms of stability and linewidth. The many lasers are required for the different process steps of a quantum computer: generating, cooling, capturing, and preparing the atoms or ions and generating the entanglement. In the past, the technology required for one qubit filled a vibration-cushioned optical laboratory bench that weighed a hundred kilograms. In the first step, it has been possible to accommodate this setup, including lasers, in a head-high control cabinet. Even that was very challenging. The next step is to miniaturize the technology even further. This is because quantum computers not only need one qubit, but 50 or more to carry out practical computing operations; if you include error correction, another order of magnitude is needed. To achieve this, we need completely different, more compact and more powerful laser systems which must still be affordable. We are working on this to translate scientific acuity into industrial products and be able to service the quantum markets in the coming decades. The focus is on miniaturization and solutions that generate a thousand individually controllable beams simultaneously with one laser system and then couple them accordingly into the quantum computer systems.

Professor Bloch, what do you use lasers and other photonic tools and methods for in your research?

Bloch: Our main focus is on quantum computing and quantum simulators. We use lasers to cool atoms so that we can capture them with laser tweezers and to position them and arrange them spatially. And we need extremely stable, low-noise laser systems to manipulate the qubits. At present, we are actually experiencing the technological limits that Dr. Renner spoke of. It is an extremely complex task to keep the many different laser systems running and to control them. I would immediately use the rack with 1000 beams from one laser that was mentioned (laughs). We need reliable, easy-to-operate, compact solutions that can also be modularized in the future. To this end, we are collaborating with industrial partners to whom we explain our requirements and existing bottlenecks in the application.

Dr. Renner, today’s approaches for quantum computers are only partly based on photonics. In which applications do you see more market potentials for the photonics industry?

Renner: I would like to contradict you there. Most approaches in quantum computing are optically controlled. But it is simply a fact that the companies that back superconductors are more prominent in the media at the moment. It remains to be seen who will win the race. There are at least four very promising technologies that use photonics intensively: ion and neutral atom-based approaches, photonic quantum computers and the approach based on color centers in diamond. Companies like IonQ, Pasqal, Alpine Quantum Technologies GmbH (AQT), Coldquanta, and Honeywell Quantum Solutions have outstanding concepts. In many cases, only the number of qubits is considered when comparing approaches. But their coherence time, gatter fidelity and connectivity—described as quantum volume in professional circles—are also important. And here, optically controlled systems currently have a clear advantage.

Bloch: The necessary cooling of the equipment alone makes scaling difficult. With millions of qubits, this would require enormous cryostats, which simply don’t exist. This illustrates a little the challenges and the current state of the art. Scaling requires optimized process control—and it is completely unclear which of the described technology paths will produce the best result. But one thing is clear: the optical approaches (especially with ions and atoms) are pursued primarily in Europe and we have a very good technological basis with a strong photonics industry and research. We can certainly set the trend.

Renner: I agree. No matter whether we are talking about lasers, frequency combs and detectors or the wide range of user industries: Europe has the best requirements to shape the market. Here, we have users that want to carry out the highly complex simulations and computing operations with the help of quantum computing, such as chemical and pharmaceutical companies, insurance companies and banks and also the increasingly networked mobility sector on rail and road.

Bloch: Apart from computers, we have quantum metrology and sensors and, in quantum communications, there is a high level of demand from the industries that are based here. Here, too, large markets for photonics are opening up. Atomic clocks, gravimeters, navigation systems, for example. Currently, in many cases the driver is the vision of quantum computing. But I am convinced that every advance that we make in this area will stimulate all other applications and markets. Better clocks, more precise trace gas analyses, or more sensitive measuring instruments. And, of course, more accurate, more efficient, and lower-noise lasers. The beauty is that the areas of application are linked with each other technologically. When you have built an atomic clock, you already have half the stretch to quantum computers behind you. In other words, on the road to quantum computers many potential products are created for which there is already a market and, consequently, potential sources of income…

…that take laypeople like me to the limit of their mental capacity. Demands for precision are enormous where atoms are cooled by laser and individual photons are counted and manipulated. How can your processes, which are implemented in many-body systems, be measured and controlled?

Bloch: Currently, we typically control about 1000 atoms, which we can position, control, and move perfectly with defined distances in space. With the current systems, we can also control their states well. In quantum simulation, we are mainly interested in the interactions between these atoms. We can specifically adjust them and then photograph the atoms directly and analyze the photos precisely by reading the position of every single atom.

Seriously: photos?

Bloch: Yes, we can determine the distances of laser-cooled atoms relatively freely with laser tweezers or with the help of diffraction gratings and are working here in the micrometer range. This can be depicted optically very well. We are not concerned about the absolute length scales but rather the relationship between physical length scales. As opposed to taking a look into a material and its atoms with an X-ray microscope, we pull the atoms apart randomly and more or less “enlarge the material” and then look at how it reacts to external influences.

A frequently heard complaint is that the gap between research and application is too large. How is TOPTICA able to keep pace with scientific research and derive practical products from it?

Renner: We are able to do this because we work so close to the research. On average, our employees—I already mentioned the high number with a doctor’s degree—are between 30 and 40 years old, have usually carried out experiments with photonic instruments during their studies and, as a result, know what matters. Through them alone, we have close contact to current research. And about 10,000 of our lasers are currently being used in scientific quantum optics applications. Many meetings are held before a laser is sold: consultation, specification, or planning the laboratory setup. This exchange of experiences in both directions helps us keep on top of things and offer solutions that really help the users. Other driving forces come from funded projects that we take part in. In quantum technologies alone we are currently cooperating in about a dozen projects.

Professor Bloch, if you were to write a wish list of photonic innovations for your research, what would be your three most important wishes?

Bloch: I would like not having to bother about the lasers. And if something breaks down, I would like to be able to replace the respective module and continue working. That’s where we want to be. How these systems are designed in detail, whether with many lasers or with beam multiplexing with modulators, is unimportant to us. What is important are functionality and performance. Systems that can switch lasers quickly with a high contrast ratio and that can use the required wavelengths without complications—low-noise systems with stable frequencies and minimum linewidth. We always need the best to keep pushing the boundaries of what is feasible. Perhaps I will see the rack with 1000 beams from one laser that we talked about earlier before the end of my career.

Renner: We’ll manage that before you retire (he laughs).

Sounds interesting. Are there physical and technical obstacles that you would have liked to have overcome already to pave new ways for quantum research?

Renner: Mr. Bloch’s wish list includes the challenging problems that have to be solved. In some cases, we can use solutions from other areas. For example, in confocal microscopy it is state of the art that the different lasers with different wavelengths have wandered from the side table into the device. These days, you find the corresponding modules with half a dozen lasers that are activated and coupled with a mouse click. We are also striving to achieve this state of the art in quantum systems. The challenges are that the required linewidths are very narrow and the stability demands are very high. In addition, the preferred difficult wavelengths—often in the UV range—increase development efforts and costs. We won’t be short of work in laser development, electronic controls, material development or photonic integrated circuits (PICs) for a long time. With the second quantum revolution, our industry has some exciting times ahead of it.