Controlling fully integrated nanodiamonds

November 23, 2020

Using modern nanotechnology, it is possible nowadays to produce structures which have a feature sizes of just a few nanometres. This world of the most minute particles - also known as quantum systems - makes possible a wide range of technological applications, in fields which include magnetic field sensing, information processing, secure communication or ultra-precise time keeping. The production of these microscopically small structures has progressed so far that they reach dimensions below the wavelength of light. In this way, it is possible to break down hitherto existent boundaries in optics and utilize the quantum properties of light. In other words, nanophotonics represent a novel approach to quantum technologies.

As individual photons move in the quantum regime, scientists describe the relevant light sources as quantum emitters that can be embedded in nanodiamonds, among others. These special diamonds are characterized by their very small particle size, which can range from just a few to several hundred nanometres. Researchers at the University of Münster have now succeeded for the first time in fully integrating nanodiamonds into nanophotonic circuits and at the same time addressing several of these nanodiamonds optically. In the process, green laser light is directed onto colour centres in the nanodiamonds, and the individual red photons generated there are emitted into a network of nano-scale optical components. As a result, the researchers can now control these quantum systems in a fully integrated state. The results have been published in the journal Nano Letters.

Background and methodology

Previously, it was necessary to set up bulky microscopes in order to control such quantum systems. With fabrication technologies similar to those for producing chips for computer processors, light can be directed in a comparable way using waveguides (nanofibres) on a silicon chip. These optical waveguides, measuring less than a micrometre, were produced with the electron-beam lithography and reactive ion etching equipment at the Münster Nanofabrication Facility (MNF). "Here, the size of a typical experimental set-up was shrunk to a few hundred square micrometres," explains Assistant Professor Carsten Schuck from the Institute of Physics at the University of Münster, who led the study in collaboration with Assistant Professor Doris Reiter from the Institute of Solid State Theory. "This downsizing not only means that we can save space with a view to future applications involving quantum systems in large numbers," he adds, "but it also enables us, for the first time, to control several such quantum systems simultaneously." In preliminary work prior to the current study, the Münster scientists developed suitable interfaces between the nanodiamonds and nanophotonic circuits. These interfaces were used in the new experiments, implementing the coupling of quantum emitters with waveguides in an especially effective way. In their experiments, the physicists utilized the so-called Purcell effect, which causes the nanodiamond to emit the individual photons with a higher probability into the waveguide, instead of in some random direction.

The researchers also succeeded in running two magnetic field sensors, based on the integrated nanodiamonds, in parallel on one chip. Previously, this had only been possible individually or successively. To make this possible, the researchers exposed the integrated nanodiamonds to microwaves, thus inducing changes of the quantum (spin) state of the colour centres. The orientation of the spin influences the brightness of the nanodiamonds, which was subsequently read out using the on-chip optical access. The frequency of the microwave field and therewith the observable brightness variations depend on the magnetic field at the location of the nanodiamond. "The high sensitivity to a local magnetic field makes it possible to construct sensors with which individual bacteria and even individual atoms can be detected," explains Philip Schrinner, lead author of the study.

First of all, the researchers calculated the nanophotonic interface designs using elaborate 3D simulations, thus determining optimal geometries. They then assembled and fabricated these components into a nanophotonic circuit. After the nanodiamonds were integrated and characterized using adapted technology, the team of physicists carried out the quantum mechanical measurements by means of a set-up customized for the purpose.

"Working with diamond-based quantum systems in nanophotonic circuits allows a new kind of accessibility, as we are no longer restricted by microscope set-ups," says Doris Reiter. "Using the method we have presented, it will be possible in the future to simultaneously monitor and read out a large number of these quantum systems on one chip," she adds. The researchers' work creates the conditions for enabling further studies to be carried out in the field of quantum optics - studies in which nanophotonics can be used to change the photo-physical properties of the diamond emitters. In addition to this there are new application possibilities in the field of quantum technologies, which will benefit from the properties of integrated nanodiamonds - in the field of quantum sensing or quantum information processing, for example.

The next steps will include implementing quantum sensors in the field of magnetometry, as used for example in materials analysis for semi-conductor components or brain scans. "To this end", say Carsten Schuck, "we want to integrate a large number of sensors on one chip which can then all be read out simultaneously, and thus not only register the magnetic field at one place, but also visualize magnetic field gradients in space."

University of Münster

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to