Diamond and lithium niobate are combining to serve as a key component of future quantum technologies. Diamond and lithium niobate are often touted as highly efficient quantum materials. Now, as a result of support from the Q-NEXT Center, scientists have combined the two materials into a single quantum device with exciting results.

Quantum information scientists are constantly searching for winning combinations of materials that can be manipulated at the molecular level to reliably store and transmit information.

Following a recent proof-of-principle demonstration, researchers are adding a new combination of compounds to the list of quantum materials.

In a published study ACS PhotonicsThe researchers combined two nanoscale structures, one made of diamond and the other of lithium niobate, on a single chip. They then directed the light from the diamond to lithium niobate and measured the fraction of light that successfully passed through. The larger this ratio, the more effective the coupling of materials and the more promising the coupling as a component of quantum devices.

The result: An extraordinary 92% of the light passed from diamond to lithium niobate.

The research was supported in part by Q-NEXT, the National Quantum Information Research Center under the U.S. Department of Energy’s (DOE) Argonne National Laboratory. The study was conducted by Amir Safavi-Naini and Jelena Vukovich from Stanford University.

A little about qubits

Quantum technologies use properties of matter at the molecular level to process information. Quantum computers, networks and sensors are expected to have a great impact on our lives in areas such as medicine, communications and logistics.

Quantum information is transmitted in packets called qubits, which can take many forms. In the research group’s new platform, qubits transfer information as particles of light.

Reliable qubits are critical for technologies such as quantum communications networks. In quantum networks, as in traditional networks, information is transferred from one node to another. Hard qubits store information inside the node; Flying qubits carry information between nodes.

The research group’s new chip will form the basis of a stable qubit. The more reliable the stable qubit, the more reliable the quantum network, and the greater the distance the networks can travel. A continent-spanning quantum network is within reach.

Material advantage

Diamond has long been touted as a great home for qubits. First, the molecular structure of diamond can be easily modified to accommodate stable qubits. On the other hand, a qubit placed on diamond can store information for a relatively long time, meaning more time to perform calculations. In addition, calculations made using diamond qubits show high accuracy.

Diamond’s partner in the group’s research, lithium niobate, is another star player when it comes to quantum information processing. Its special properties give scientists versatility, allowing them to change the frequency of the light passing through it. For example, researchers can apply an electric field or mechanical stress to lithium niobate to tune how it directs light. It is also possible to change the orientation of the crystal structure. Doing this at regular intervals is another way to shape the passage of light through the material.

“You can use these properties of lithium niobate to transform and modify the light coming from diamond, modulating it in ways that are useful for different experiments,” said Jason Herrmann, a PhD student and co-author of the paper. student at Stanford. “For example, you can convert light to the frequency used by the existing communications infrastructure. So these properties of lithium niobate are really beneficial.”

A strong couple

Traditionally, light from qubits placed inside diamonds is directed either into a fiber optic cable or into free space. In both cases, the experimental setup is cumbersome. Fiber optic cables are long, dangling and flexible. And transferring qubits into free space requires large equipment.

All this hardware disappears when the light from the diamond qubits is directed to lithium niobate. Almost any component can be placed on a single small chip.

“There is an advantage to having as many of your devices and functions as possible on a single chip,” Lee said. “It’s more stable. And it really allows you to miniaturize the installation.”

Not only that, but because the two devices are connected by a thin filament (1/100th the width of a human hair), the quantum light is squeezed into a narrow passage leading to the lithium niobate, increasing the interaction of the light with the material and making it easier to control the properties of the light.

complex assembly

One of the challenges in developing the platform was modifying the diamond, which is only 300 nanometers wide, to align with lithium niobate.

“We had to move the diamond around with little pins until it looked like it was in the right place on the plate,” Lee said. “It’s like you’re poking with little sticks.”

Measuring the transmitted light was another challenge.

“We have to make sure we take into account all the places where light passes or is lost so that we can say, ‘This is it from diamond to lithium niobate,'” Herrmann said. “This calibration measurement required us to go back and forth a lot to make sure we got it right.”

The team is planning further experiments that will exploit the quantum information provided by diamond and lithium niobate, individually or in combination. Their latest success is just a milestone in what they hope will be a diverse menu of devices based on the two ingredients.

“By combining these two material platforms and directing light from one to the other, we show that you can truly have the best of both worlds, rather than working with just one material,” Lee said.