Optics column丨Light in quantum technology development and future

Immanuel Bloch, Director of the Max Planck Institute for Quantum Optics, Professor of Experimental Physics at the University of Munich and one of the speakers at the Munich Center for Quantum Science and Technology (MCQST), a cluster of excellence, recently discussed with Dr. Thomas Renner, CEO of TOPTICA Photonics AG, the current demand for lasers and photonic solutions for quantum technology applications and the developments we can expect to see in the future.

Left: Thomas Renner; Right: Immanuel Bloch

Q: Professor Bloch, a quick question in advance. What is the Munich Cluster of Excellence (MCQST)? Is the focus on basic research or specific applications?

Bloch: The cluster focuses more on basic research. But in Munich, we also have the Munich Quantum Valley, which focuses on application-related technology development. These two initiatives are interconnected and cover the entire spectrum of quantum computing and simulation, from quantum communication to applications in metrology and sensors.

Education is a key pillar of MCQST. For example, we have established a master's program in quantum science and technology, which is very popular. In this year alone, we had 300 international applications, of which we accepted about 100. This industry is calling for graduates to meet the many challenges of this future industry.

Q: Dr. Renner, the second quantum revolution is currently taking place in the sciences. But even so, how big is the market for TOPTICA?

Renner: We also divide the field into basic research and applications, and our roots are in science. toptica was founded as a scientific spin-off company almost 25 years ago and still has very close ties to research. Of our 400 employees, 60 have PhDs 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. In implementing laser systems and other photonic solutions, we derive stimulation from research, which benefits us in all other user industries.

This is because in the field of science, the requirements for precision and stability are very high. If success is achieved here from the technical side, it will benefit in all other areas. Now, quantum technology is ready to make the leap from basic research to industrial applications. As a result, there are new requirements in terms of system design and size, price level and availability. In this regard, we have been supplying about 50% of our lasers to industrial customers for many years, which has benefited us greatly.

Q: Can you describe in more detail some of the changes that are coming?

Renner: Quantum applications, such as quantum computers, are relatively well understood scientifically. But now, a single quantum bit requires up to a dozen different wavelengths of lasers that do not fall into the classical standard wavelengths, such as 633 or 1064 nanometers. These lasers must also meet the highest requirements in terms of stability and linewidth. The different process steps of a quantum computer require many lasers: generation, cooling, trapping and preparation of atoms or ions, and generation of entanglement.

In the past, the technology required for one quantum bit filled an optical laboratory bench with vibrating pads weighing up to a hundred kilograms. In a first step, it has been possible to accommodate such a setup, including lasers, in a head-high control cabinet. Even this was very challenging. The next step is to miniaturize the technology even further. This is because quantum computers require not only one quantum bit, but 50 or more quantum bits to perform the actual computational operations; another order of magnitude is needed if error correction is included. To achieve this, we need radically different, more compact and more powerful laser systems that must still be affordable.

We are working to translate the scientific acumen into industrial products that can serve the quantum market for decades to come. The focus is on miniaturization and solutions that generate a thousand individually controllable beams simultaneously with a single laser system and then couple them accordingly into a quantum computer system.

Q: Professor Bloch, how do you use lasers and other photonic tools and methods 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 localize and spatially align them. And we need extremely stable, low-noise laser systems to manipulate quantum bits. Right now, we're actually going through the technical limits that Dr. Renner talked about: it's an extremely complex task to keep many different laser systems running and to control them. I would immediately use the mentioned rack with 1000 beams for one laser.

We need reliable, easy-to-operate, compact solutions that can also be modularized in the future. To this end, we are working with our industrial partners to explain our requirements and existing bottlenecks in our applications.

Q: Dr. Renner, today's approach to quantum computers is only partially based on photonics. In which applications do you think the photonics industry has more market potential?

Renner: I would like to rebut you here. Most approaches to quantum computing are optically controlled; however, it is just a fact that companies supporting superconducting technologies are currently more prominent in the media. It remains to be seen who will win this race. There are at least four very promising technologies that use photonics intensively: methods based on ions and neutral atoms, photonic quantum computers, and methods based on diamond NV color centers. Companies like IonQ, Pasqal, Alpine Quantum Technologies GmbH (AQT), Coldquanta and Honeywell Quantum Solutions have outstanding concepts. In many cases, only the number of quantum bits is considered when comparing various methods; however, their coherence time, fidelity and connectivity (described as quantum volume in specialized fields) are also important. And here, optical control systems currently have a clear advantage.

Bloch: The necessary cooling of the device alone makes scaling difficult. If there were millions of quantum bits, this would require huge cryogenic chambers, which simply do not exist. This illustrates the challenge and the current state of the art. Scaling requires optimal process control, and it is not at all clear which of the described technical paths will yield the best results. But one thing is clear: optical methods (especially with ions and atoms) are mainly performed in Europe, and we have a very good technological base with a strong photonics industry and research. We can certainly lead the way.

Renner: I agree. Whether we are talking about lasers, frequency combs and detectors or a wide range of user industries. Europe has the best requirements to shape the market. Here we have users who want to perform highly complex simulations and computational operations with the help of quantum computing, such as chemical and pharmaceutical companies, insurance companies and banks, as well as the increasingly connected mobile sector on railroads and roads.

Bloch: In addition to computers, we have quantum metrology and sensors, and there is a high demand for the industry here in terms of quantum communications. Large markets are opening up here for photonics as well. Examples include atomic clocks, gravimeters, navigation systems, etc. Currently, in many cases, the driving force is the vision of quantum computing. But I believe that every advance we make in this area will stimulate all other applications and markets. Better clocks, more accurate analysis of trace gases, or more sensitive measurement instruments. And, of course, more accurate, more efficient and less noisy lasers. The beauty of this is that these application areas are technically interconnected. When an atomic clock is built, half of the time will be applied to the study of quantum computers. In other words, there is already a market for many potential products, and therefore a potential source of revenue, on the road to quantum computers.

Q: The demand for precision is enormous, where atoms are cooled by lasers and individual photons are counted and manipulated. How do you measure and control the processes implemented in a multi-body system?

Bloch: Currently, we typically control about 1,000 atoms, which we can position, control, and move them perfectly in space at a defined distance. With the current system, we can also control their states very well. In quantum simulations, we are mainly interested in the interactions between these atoms. We can adjust them and then photograph the atoms directly and read the position of each atom to analyze the photo precisely.

Q: What does a photograph mean?

Bloch: We can determine the distances of laser-cooled atoms relatively freely with laser tweezers or with the help of diffraction gratings, and work in the micrometer range here. This can be well described optically. We are not concerned with absolute length scales, but with the relationship between physical length scales. As opposed to looking at a material and its atoms with an X-ray microscope, we pull the atoms apart randomly, more or less "amplify the material", and then see how it responds to external influences.

Q: A common complaint is that the gap between research and application is too wide. how can TOPTICA keep pace with scientific research and get practical products from it?

Renner: We are able to do this because we work very close to the research. On average, we have a large number of employees with PhDs, between 30 and 40 years old, who have usually performed experiments with photonic instruments during their studies, and therefore know what is important. Through them alone, we are in close contact with current research. And about 10,000 of our lasers are currently being used in scientific quantum optics applications. We hold many meetings before selling our lasers: consulting, specification or planning lab setups.

This two-way exchange of experience helps us to stay ahead of the curve and provide solutions that really help our users. Other drivers come from the funded projects we are involved in. In quantum technology alone, we are currently collaborating in a dozen projects.

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

Bloch: I would like to not have to worry about lasers. If something breaks, I would like to be able to replace the appropriate module and continue to work. That's what we hope to achieve. It doesn't matter to us how detailed these systems are designed, whether they use many lasers or modulators for beam multiplexing. What matters is functionality and performance. Systems that can switch lasers quickly with high contrast, that can use the desired wavelengths without complications: low-noise systems with stable frequencies and minimal linewidths.

We always need the best to keep pushing the boundaries of what is feasible. Maybe before my career is over, I'll see the rack of 1000 beams for one laser we talked about earlier.

Q: That sounds interesting. Are there any physical and technical hurdles that you wish had been overcome in order to pave new paths for quantum research?

Renner: Mr. Bloch's wish list includes challenging problems that must be solved. In some cases, we can use solutions from other fields. For example, in confocal microscopy, lasers of different wavelengths have wandered into the device from the table next to it, which is a state of the art. These days, you'll find corresponding modules with half a dozen lasers that can be activated and coupled with a mouse click. We are also working on achieving this state of the art for quantum systems. The challenge is that the required linewidth is very narrow and the requirements for stability are very high. In addition, the preferred difficult wavelengths are usually in the ultraviolet range, which adds to the development effort and cost.

We will not be short of work in laser development, electronic control, materials development, or photonic integrated circuits (PICs) for a long time; an exciting time for our industry is ahead with the advent of the second quantum revolution.

Reference link：

https://world-of-photonics.com/en/newsroom/photonics-industry-portal/photonics-interview/quantum-technologies/