Questions&Answers: Diamond in Quantum Applications

What are the unique properties of diamond that make it a supermaterial?

Diamond has long been known to have exceptional properties, largely resulting from the symmetry of the cubic lattice made of light carbon atoms connected by extremely strong bonds. These exceptional properties include thermal conductivity five times higher than that of copper and the widest optical transparency of any material extending from the UV to the RF part of the electromagnetic spectrum. Additionally, diamond also has some interesting chemical properties as it is extremely inert, though it can become a conductor by adding boron.

In this manner, one could leverage synthetic diamond for use in electrochemical incineration where existing electrode materials have only a limited lifetime.

What are the traditional applications for synthetic diamond in engineering and electronics?

Historically diamond has been exploited mainly for its great hardness in mechanical applications. For example in modern cars more than 150 components are made using a variety of diamond tools. However in the past two decades there have been an increasing number of applications which utilize some of diamonds’ other superlative properties. For example, synthetic diamond is utilized in semiconductor applications for its heat spreading abilities. This trend is being driven by the increasing number of transistors on a chip which increases the thermal load and therefore runs the risk of device failure. Using diamond in this application not only means more transistors can run on a chip but it also extends device lifetime as they can run cooler. Synthetic diamond is also being used as a radiation detector. Element Six diamond is currently being used in the CERN Large Hadron Collider as part of its monitoring system.

Is synthetic diamond suited for quantum technology applications?

Quantum information and the manipulation of quantum information are key to the development of the next generation of quantum technologies. However quantum information is fragile and easily lost through interactions such as heating. This is why most quantum experiments in the lab are typically performed at temperatures approaching absolute zero or extreme lengths are gone to in order to isolate objects from interactions, such as trapping single atoms with lasers. However while isolated atoms and their quantum properties can be probed and controlled, building technology on these kinds of platforms is a significant engineering challenge when compared to using solid state platforms such as silicon. Diamond is a unique material for quantum technology in that certain defects, such as the nitrogen vacancy (NV) defect, have quantum properties that can be easily probed and controlled, much like isolated atoms, only they are now located in a crystal. The reason for this is that unlike most materials, the diamond crystal lattice forms a low ‘noise’ environment so that fragile quantum properties are not lost at room temperature, and information can be stored and probed for longer time periods. Synthetic diamond is perfectly suited for this area as the material can be grown containing the NV defects such that the material properties can be controlled for specific applications.

What properties does diamond have that make it uniquely suited for quantum technologies?

MM: Given that diamond provides this low noise environment for defects is not enough to make it a useful quantum material. The key is the combination of both the material and the defects which are being used as the quantum resource. In this respect the key properties are, firstly, the ability to control the quantum state of the electronic spin associated with the NV center as it can be easily manipulated using external green light and microwaves. Secondly, the coherence or life time of the quantum information is very long, even at room temperature, due to a combination of physics and the high purity inert diamond lattice. Thirdly, the quantum state can be easily readout by measuring the amount of red luminescence being emitted by the NV spin defect. Lastly, it is important to take advantage of quantum effects such as entanglement. Using diamond, this can be achieved by entangling multiple defects by interactions within the bulk diamond lattice or via entanglement of emitted photons (luminescence) coming from the defects.

Does diamond have multiple quantum applications?

MM: There is a wide range of potential applications for diamond quantum technologies. Magnetic sensing provides an example; when using diamond quantum technology it demonstrates extreme promise with many proof of concept applications in material characterization, such as nano-imaging hard drive write heads for next-generation magnetic hard drives, or in biological imaging, such as measurements of neuron activity in marine worms. However, magnetic sensing is just the tip of the iceberg.  New sensing methods for pressure and temperature, and the alluring possibility of diamond-based quantum computing on the horizon makes this an exciting and productive space to be working in.

How do you engineer diamond for quantum technologies?

MM: Element Six uses a process known as chemical vapor deposition (CVD) to grow our diamonds for quantum technologies. This process consists of creating a plasma using microwaves which contain hydrogen and a carbon containing gas. The hydrogen plays a key role in the process, enabling us to grow diamond at temperatures and pressures where diamond is not thermodynamically stable. An example of this is stabilizing the surface against forming graphite.

With the CVD process, single crystal diamond grows on diamond seeds that are placed in a reactor enabling the diamond to grow in layers. By controlling the process conditions and the input gases, such as adjusting the nitrogen dopant gas concentration — as nitrogen is the component used to form the NV defect — we are able to control the purity on the nanoscale and chemical composition of the diamond.

Can you describe a few recent experiments where synthetic diamond has enabled advancements in these quantum applications?

Element Six has been working with a team led by Ronald Hanson at the Delft University of Technology, which has demonstrated some amazing fundamental science using our diamond. This is all based on probing our understanding of quantum mechanics and a particular process called entanglement that Albert Einstein called “spooky action at a distance.” It’s a process in which two particles become strongly connected, to the point that they are always correlated regardless of the distance between them. Previous experiments probing this quantum principle have shown it to be true, but always with the caveat of loopholes—there existed other possible interpretations consistent with the data. It wasn’t until last year that this test, known as the Bell Test, was demonstrated and closed all the loopholes—definitively proving the principle of quantum entanglement.

With this experiment, a team of researchers at Delft University of Technology used two CVD diamonds, from Element Six, each containing a NV defect. These defects then emitted indistinguishable particles of light (photons) that contained the quantum information from the defects, and the team was able to quantum-mechanically entangle the two defects over a distance of 1.3 km.

We have also collaborated with Jörg Wrachtrup’s group at the University of Stuttgart and its development of magnetic sensors for write heads in magnetic hard-disk drives. Currently there are no established sensors that can resolve the magnetic field of write heads on the scale of 5–10 nm, which is critical for the next generation of hard disk drives. In recent work using the NV defect in diamond the basic principles have been demonstrated to analyze these write heads with high spatial sensitivity. This is really exciting as it shows real-world practical examples where quantum technology can impact everyday lives. 

If diamond continues to be leveraged for successful developments in quantum science, what major breakthrough(s) do you think could be uncovered in the near future?

We foresee that diamond will continue to be used as a tool to aid understanding of the quantum world. However the real excitement is what the possibilities of this technology will enable. Currently, brain imaging using MRI is limited by the sensitivity of the sensors. Potentially, diamond magnetic field sensing will provide a new method to image the brain with greater sensitivity and resolution. We can see that using this as a new tool in medical imaging will enable new breakthroughs in the understanding of how the brain works along with new diagnostic methods and treatments.

What are some of the technical challenges developers face in making practical quantum devices?

MM: The biggest technical challenges in making a practical diamond device is linking the material, the quantum science and the device engineering together. Doing so requires a strong collaboration among material scientists, physicists and engineers. The longer term challenges for areas such as quantum computing involve making each of the defects in the diamond crystal behave in an identical way in order to scale the systems. This is a very challenging proposition, however many groups are working on the architecture of such a system to reduce the engineering requirements.

What types of applications will the first commercially-viable diamond-based devices support? And when can we expect to see them come to market?

The areas that are closest to market are magnetic sensing devices, although even in this area, there are multiple variants of the technology. For example, by using many NV defects together highly sensitive magnetic field sensors have been constructed to image biological samples. At the other extreme, single NV defects have been used as tools for material characterization.

How does Element Six plan to work with academia and other organizations to help turn synthetic diamond based quantum technologies in to commercially available devices?

In the nascent area of quantum technologies successful collaboration among academia and industry with government support is critical. No one entity is capable of converting the huge potential quantum mechanics offers alone.  Element Six has worked closely with many academic groups to further our knowledge but also to enable us to bridge the gap between the material and devices with other commercial organizations.  Government has multiple roles from funding support for long term initiatives to setting protocols and regulations that will generate radical new quantum-enabled solutions.

How long has Element Six been involved in this space?

Element Six began working on quantum technologies in 2007. At this time we were part of an EU collaboration called the Engineered Quantum Information in Nanostructured Diamond (EQUIND) project, which was essentially building a toolbox for diamond quantum computing. This involved various aspects and our role focused on the material synthesis and processing. Up until this point nearly all the work that was performed on diamond was based on a single natural diamond which had amazing quantum properties compared to other natural diamonds. This diamond had been cut into many pieces and distributed to the top academic groups in the world. However, as more of our synthetic material was used in academia it started to be used as the main source of material for the development of diamond quantum technologies.

Who has Element Six collaborated with to develop new quantum technologies?

Element Six has been working in this area for a long time and we have developed many collaborations with academic groups in both Europe and the U.S. In the last five years we’ve experienced in an increase in industrial demand, and incubations have also started represented by start-ups, small companies and even multinational corporations across the U.S. and EU.