“Our dream is a real-time high spatial resolution of Etna’s gravity map”

MuQuans (µQuans) from Bordeaux is specialized in quantum sensor technology. Among other things, the spin-off of the Institut d'Optique d'Aquitaine has developed a unique quantum gravimeter with which absolute gravitational measurements in µGal resolution (billionth of acceleration due to gravity) are possible. In our interview, founder and CEO Bruno Desruelle talks about measurements at the Sicilian volcano Etna, technological and economic perspectives of quantum sensors as well as the funding situation in the field of quantum technologies.

Monsieur Desruelle, can you briefly introduce us to your company µQuans?

Bruno Desruelle: We are a high technology company specialized in quantum technology that exists for almost ten years now. We have developed a complete portfolio composed of various kinds of high performance measurement solutions, based on quantum manipulation of laser-cooled atoms. In particular, we provide quantum gravity sensors dedicated to the geophysics-market, besides high performance atomic clocks dedicated to time or frequency metrology. We are also offering different types of laser solutions optimized for quantum physics either in fundamental research or in applications. Our company is located in Bordeaux, has 30 high skilled employees and it is tightly connected to academic research. In the field of quantum optics that is essential: We constantly integrate findings from basic research and complement our team with outstanding experts. We work closely with the LP2N - Institut d'Optique Graduate School Bordeaux and the LNE-SYRTE - Observatoire de Paris. Core technologies for our products were developed there in the 15 to 20 years before µQuans was founded.

What skills does a quantum technology company need?

Desruelle: When you are playing with the atoms, you need to force nature in this regime: you need ultrahigh vacuum, tightest control of magnetic fields, very specific laser systems with accurately controlled frequencies and so on. On the other hand, it is our goal that users can operate our systems without being quantum physicists. We hide the complexity from the users in terms of usability. This requires, among other things, very good software. All in all, we need highly specialized experts for lasers, optics, electronics, software and engineering and a close connection to the scientific community.

At LASER 2019, you reported about measurements at the volcano Etna. What is it all about?

Desruelle: Years ago, Italian geophysicists contacted us. They plan to establish a complete gravity monitoring of the volcano. For this project, we have developed our Absolute Quantum Gravimeter. We expect to set up the whole instrumentation in June 2020. The general idea is, to map the gravity field at the surface to get highly resolved information about what is below the surface. Are there cavities? And if so, are they empty or filled with fluids or rocks? We can read this information out of the size of the gravity field. By monitoring the volcano over a long time, we want to reach a better understanding of the processes inside the volcano. For example, if magma flows, the gravity field rises. In the long term, it is our goal, to predict eruptions in order to gain time for an evacuation. Our dream is a real time high spatial resolution of Etnas gravity map. Our Absolute Quantum Gravimeter is ready for that. It needs nearly zero maintenance and automatically fulfils gravity measurements at the µGal level for months or even several years.

How do you describe the function of your Absolute Quantum Gravimeter to non-technicians?

Desruelle: You might compare it with a Newton experiment; but instead of the apple, we drop a cloud of laser-cooled atoms in a vacuum chamber. By characterizing the vertical acceleration of this free falling atom cloud, we can deduce the gravitational forces. That is the easy version. It took years, to miniaturize the system and still reliably convert the cooling of the atoms into the micro-Kelvin range. When we turn the laser off, the cloud falls. To measure the acceleration, we have developed an atom-interferometer that is sensitive to gravity and exploits the wave characteristics of the cooled atoms, which is highly complex. We have succeeded in transferring a room-filling experimental setup into a compact measuring instrument with a sensor head of 38x70 cm and 25 kg, which typically works with 250 Watts of electricity. It´s function in the Etna project is the absolute gravity measurement. The geophysicists plan to install a network of plenty of small MEMS-based gravimeters on the volcano’s surface. Our Absolute Quantum Gravimeter will collect reference data to compensate the drift of the MEMS-gravimeters. If the quality of the small gravimeters isn´t sufficient, it is also possible to create a map by moving our instrument.

What are the key advantages of quantum gravimetry compared to other methods?

Desruelle: First, it provides very high performance measurements in µGal-resolutions; this is equal to one billionth of the earth acceleration. Second, it provides an absolute Gal-value without any drift for an extremely long period of time, which predestines it for long-term monitoring. Third, it is very easy to operate and robust. We have no moving parts in our vacuum chamber and use very reliable lasers from the telecom sector. This bundle makes it very interesting for geophysical applications. Most of today’s gravimeters suffer from huge drift and are temperature sensitive. That makes it difficult for their users to differentiate real geophysical signals from false measurements.

However, aren’t µGal-resolutions way too fine? How do you compensate other vibrations?

Desruelle: This is in fact a severe problem. We had to find a solution to compensate seismic noise, which might have its origin in road traffic or even crowds of tourists climbing around the Etna. These seismic signals exceed the µGal range by orders of magnitude. Our solution took years of research together with the LNE-SYRTE in Paris. We´ve implemented a very powerful hybridization-technique. It combines the atomic signal with measurements provided by a classic accelerometer and makes use of real-time data processing to reject the contribution of seismic noise.

What is your assessment of the market potential of quantum sensors and where are the fields of application?

Desruelle: I am convinced of their market potential for a wide range of applications. We can implement quantum technologies to various kinds of measurements – usually, where high performance is needed. All over the world, we see quantum start-ups and research-projects rising. Gravity sensors are one of the major applications. Accelerometers, gyroscopes, magnetometers or clocks based on quantum optics will find their way to different markets, too. Extremely high performance solutions are in demand in space technology or in submarines, in global positioning and many more applications. In addition, there is potential in mass-markets like autonomous or electric vehicles or in medical applications like brain imaging. It is not unrealistic to expect a very large industrial impact in the next ten or twenty years.

Since you founded µQuans in 2011, quantum technology has made great progress. How do you perceive the market and the funding situation?

Desruelle: In 2011, we were alone in the hall. The idea to consider the industrial development of quantum sensors for real life applications seemed insane. People laughed at us. Today the situation is completely different. There is a broad understanding of the potential of quantum technologies. Many start-ups form, governments are interested in accelerating the development and therefore spend billions to fund research, early industrial applications and start-ups. We see many stakeholders, whether private investment firms or public bodies, who are very concerned about this and heavily invest. This is a very pleasing development. Although we may have started a little too early, we are still there - and now µQuans is years ahead of all our competitors.

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