Physicists at Purdue University have levitated nanoscale diamonds, polished them with lasers, and spun them at an incredible 1.2 billion rpm. The experiments aren’t just about creating the “world’s smallest disco,” they could also help study quantum physics.
Tiny diamonds, averaging 750 nanometers wide, are first produced under high pressure and temperature. They are then irradiated with high-energy electrons to create what is known as a nitrogen-vacancy defect, which can be used to hold quantum information.
To make the nanodiamonds float, the team created a surface ion trap by depositing a thin layer of gold onto a sapphire wafer and then etching the gold into an “omega” shape (Ω). When a current is pumped through the gold, it creates an electromagnetic field that can float a nanodiamond placed above the surface in a vacuum chamber.
Kunhong Sen
“We can change the direction of rotation by adjusting the drive voltage,” said Kunhong Shen, one of the authors of the study. “The levitated diamond can spin clockwise or counterclockwise around the z-axis shown in the schematic (perpendicular to the surface of the ion trap), depending on our drive signal. If we don't apply the drive signal, the diamond will spin in all directions like a ball of yarn.”
In doing so, the team was able to spin the nanodiamonds at speeds of up to 1.2 billion rpm. While that’s pretty impressive, it’s far from the fastest-spinning object ever — the same team currently holds that record with a nanoscale “dumbbell” spinning at an incredible 300 billion rpm.
But the nanodiamond study has a more practical purpose than just aiming for a world record. When the spinning diamonds are illuminated with a green laser, they emit their own red light, allowing the scientists to read the spin states of the electrons inside their defects. At the same time, an infrared laser is shined on the diamonds, and the pattern of how they scatter light tells the team how they spin. Comparing the two measurements allows the scientists to infer how the diamonds’ spin affects the quantum information contained in their defects.
“Imagine tiny diamonds floating in empty space, or vacuum,” said Tongcang Li, lead author of the study. “Inside these diamonds are spin qubits that scientists can use to make precise measurements and explore the mysterious relationship between quantum mechanics and gravity. In the past, experiments with these floating diamonds have had trouble preventing them from getting lost in the vacuum and reading out the spin qubits. However, in our study, we successfully levitated a diamond in a high vacuum using a special ion trap. For the first time, we were able to observe and control the behavior of spin qubits inside a diamond levitated in a high vacuum.”
The key question the team hopes to investigate is how gravity, which remains one of the most pressing problems in physics, can be explained in quantum terms.
The research was published in the journal Nature Communications.
Source: Purdue University