Quantum technology often requires the precise control of individual particles, atoms, or ions. Optical tweezers are one such device that can be used to control these particles.
Optical tweezers use focused lasers to trap and control single atoms or ions with extremely high precision. They are used in quantum computing systems, atomic clocks, and studying quantum physics.
However, trapped ions or atoms have a natural motion or jiggle due to thermal energy. This is even present when the particles are cooled to extremely low temperatures.
This jiggling introduces noise in the system, which interferes with the quantum information contained in the system.
Now, researchers from Caltech have turned this problem into a powerful resource. In a new study, the researchers use atomic motion to create hyperentanglement, a correlation of two properties simultaneously.
In regular quantum entanglement, two particles are correlated through one property, like spin. However, in the case of hyperentanglement, it can be multiple properties.
This is the first demonstration of hyperentanglement in massive particles or neutral atoms, previously seen with photons.
Harnessing motion for quantum information
To create hyperentanglement, the researchers use arrays of strontium atoms trapped using optical tweezers.
These atoms had thermal motion, which they wanted to turn into a controllable quantum resource.
They cooled the atoms to a near-complete standstill using a new method. This cooling method was inspired by Maxwell’s demon, a thought experiment from 1867.
In essence, the method involves measuring the motion of each atom and applying specific operations to eliminate the thermal motion. The decision is made one atom at a time based on real-time measurements.
Next, the researchers induce controlled oscillations in the atoms. This was done in such a way that the atoms could oscillate in two different motions simultaneously, creating a state of superposition. In simple terms, each atom can oscillate in two ways at the same time.
These oscillations have a small amplitude of around 100 nanometers, much smaller than the width of a human hair.
Following this, the researchers entangle neighboring atoms. This induces a correlated state between the atoms’ motional and electronic components. It’s like twins separated at birth who share the same name and the same type of car.
Improving performance
The cooling method, termed “detection and subsequent active correction of thermal motional excitations,” outperforms the best laser-based cooling methods today.
Co-author Prof. Manuel Endres at Caltech spoke of their work in a press release. “Basically, the goal here was to push the boundaries on how much we could control these atoms,” said Prof. Endres.
“We are essentially building a toolbox: We knew how to control the electrons within an atom, and we now learned how to control the external motion of the atom as a whole. It’s like an atom toy that you have fully mastered.”
The improved method could improve the performance of some quantum computers, which use trapped atoms as qubits.
The findings of the study are published in the journal Science.