Physicists at Purdue University have levitated nanoscale diamonds, hit them with lasers to make them flash and sent them spinning at an incredible 1.2 billion rpm. The experiments aren’t just about creating the “world’s smallest disco” but could help the study of quantum physics.
The tiny diamonds, with an average width of 750 nanometers, are first produced under high pressure and temperature. Then, they’re irradiated with high-energy electrons to create what’s known as a nitrogen-vacancy defect, which can be used to hold quantum information.
To get the nanodiamonds levitating, the team created a surface ion trap by depositing a thin layer of gold onto a sapphire wafer, then etching the gold into an “omega” shape (Ω). When a current is pumped through the gold, it creates an electromagnetic field that can levitate a nanodiamond placed above the surface, in a vacuum chamber.
An illustration of the surface ion trap that helped levitate nanodiamonds. The electron spins of the nitrogen-vacancy defects can be seen inside the diamond, while the diagram of those defects is seen in the top leftKunhong Shen
“We can adjust the driving voltage to change the spinning direction,” said Kunhong Shen, an author of the study. “The levitated diamond can rotate around the z-axis (which is perpendicular to the surface of the ion trap), shown in the schematic, either clockwise or counterclockwise, depending on our driving signal. If we don’t apply the driving signal, the diamond will spin omnidirectionally, like a ball of yarn.”
In doing so, the team managed to get the nanodiamonds spinning at speeds of up to 1.2 billion rpm. While that’s pretty impressive, it’s far from the fastest spinning object – the same team currently holds that record with a nanoscale “dumbbell” that rotated at a blistering 300 billion rpm.
But the nanodiamond study has a more practical purpose than just aiming for a world record. When the spinning diamonds are lit up with a green laser they emit red light of their own, which allows scientists to read out the spin states of the electrons inside their defects. At the same time, an infrared laser was shone on the diamonds and the pattern of how they scattered that light tells the team how they’re rotating. Comparing the two measurements allows scientists to infer how the diamonds’ spin affects the quantum information contained in their defects.
“Imagine tiny diamonds floating in an empty space or vacuum,” said Tongcang Li, lead author of the study. “Inside these diamonds, there 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 had trouble in preventing their loss in vacuum and reading out the spin qubits. However, in our work, we successfully levitated a diamond in a high vacuum using a special ion trap. For the first time, we could observe and control the behavior of the spin qubits inside the levitated diamond in high vacuum.”
The main question the team hopes to probe is how gravity could be explained in quantum terms, which remains one of the most pressing problems in physics.
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