Quantum technology transforms industry and technology

Understanding quantum physics is hard for non-physicists. Yet devices that rely on quantum technology increasingly find their way into industrial production, medicine, and consumer applications. It is no wonder that Germany’s Federal Government also recognizes the need to promote a variety of projects in this field.

COMPAMED.de sat down with physicist Dr. Arne Wickenbrock from the Johannes Gutenberg University of Mainz to talk about his current research projects and asked him to explain the mind-boggling quantum world – and why it holds so much promise for medical technology.

Dr. Wickenbrock, you are currently involved in two research projects – the MiLiQuant project and the BrainQSens project. Both are supported by the German Federal Ministry of Education and Research (BMBF). What is the purpose of each project?

Dr. Arne Wickenbrock: The MiLiQuant project focuses on "miniaturized light sources for use in industrial quantum sensors and quantum imaging devices.“ Many research settings in universities are very large, expensive to operate and susceptible to damage. This makes an industrial application difficult. We want to change that. The MiLiQuant project’s primarily focuses on the necessary light sources. As scientists, we study those applications that will subsequently be tailored to these light sources and facilitate an industrial use. We are working on two gyroscopes here in Mainz. One uses nitrogen-vacancy defect centers in diamond to measure rotation rate and the other one uses nuclear spin co-magnetometry with alkali gas cells.

What are nitrogen-vacancy centers in diamond?

Wickenbrock: Diamonds are generally transparent to visible light. A diamond only has color via so-called color centers. There are different categories of color centers. Pure diamonds are entirely made of a lattice structure of carbon. If the lattice has a nitrogen atom versus a carbon atom and another carbon atom is missing in the immediate vicinity, it creates a so-called nitrogen-vacancy center. This is a naturally occurring feature in diamonds and actually happens fairly often. These point defects have an electronic configuration similar to that of an atom and allow manipulation with laser light and spectroscopy. Spectroscopy can also be used to determine various physical properties such as magnetic fields, electric fields, as well as pressure and temperature. Using color centers in diamond, we now want to drastically miniaturize angular rate sensors and develop devices that are easier to use than current models.

The BrainQSens project aims to create a “novel brain-machine interface based on quantum sensors“. What is your part in this development?

Wickenbrock: Our task here in Mainz is to research sensors for the BrainQSens project. Right now we are developing a sensor solution for endoscopy that measures magnetic fields. The project objective is to develop a sensor that manages to detect the weak magnetic field of the auditory cortex – located in the head area. There are many highly sensitive magnetic field sensors on the market, but we focus on the sensor size and sensitivity ratio. The currently available most sensitive magnetic sensors are either so-called SQUIDs (for superconducting quantum interference device), which are very expensive to operate or magnetometers based on alkali vapor cells. We have a lot of experience with the latter here in Mainz. These devices can measure magnetic fields with up to attoTesla sensitivity. To put this into perspective: Earth's magnetic field measures about 50 microtesla, while magnetic activity in the human brain measures about one picotesla, which is about 50 million times weaker than the Earth's magnetic field. There are magnetic fields in various places throughout our body. Our heart features a very large electromagnetic field by comparison. Muscle contraction also produces magnetic fields that can be measured. Measurements are between 50 million times to 50,000 times weaker than the Earth's magnetic field. That’s why you need extremely sensitive techniques and equipment and low background noise levels.

Right now, vapor-cell magnetometers already work quite well. These devices are typically ten centimeters in length with a wire that measures the magnetic field at the tip. The devices allow for brain activity measurements and close access to the brain. That’s a good thing as magnetic fields decrease as they get farther away from the source. When it comes to magnetoencephalography, the patient’s skull dictates how close the device is to the brain. As I mentioned before, sensor size also plays an important role. Gas cells provide closer access than SQUIDs, but we are still nearly one centimeter away from the brain's surface. That’s why the BrainQSens project aims to build a highly sensitive endoscope with a miniature magnetometer sensor at the tip. We aim for one picotesla (10 ^-12 T) sensitivity. The sensors we use in this case are in the submillimeter range, measuring perhaps 60 micrometers in diameter and 200 micrometers in length. That’s essentially the sensor. You could use an intracardiac catheter to measure the magnetic field produced by the heart for example. It could also be inserted into the nose or ears to get closer to sources in the brain. Another exciting option relates to the improvement of intraoperative neuromonitoring. There are many conceivable unique applications.

What strides have you been able to make in the field of miniaturization?

Wickenbrock: We expect to be able to introduce a prototype this year where a nitrogen-vacancy center magnetometer sits on an optical fiber tip.

When will your research be completed?

Wickenbrock: The BrainQSens project ends in July 2020, while the MiLiQuant project will be completed at the end of January 2022.