Parallel Omnidirectional Atom Rearrangement with Dynamic Holograms

In the quest to build machines that can solve problems beyond the reach of today's computers, scientists are turning to the smallest building blocks of matter: individual atoms. To use these atoms as the bits of a quantum computer, researchers must first arrange them into precise, defect-free patterns, much like placing tiny marbles into a grid. The challenge lies in moving these atoms without disturbing them. If the tools used to grab and shift the atoms are too slow, the process takes too long; if they are too fast or change too abruptly, the atoms can be shaken loose or heated up until they fly away. For years, scientists have been trying to find the perfect balance, seeking a way to rearrange thousands of these atoms simultaneously, in any direction, and with enough speed to keep the delicate quantum information intact.

A team of researchers at Harvard University has now demonstrated a method that achieves this balance, allowing them to move and reconfigure nearly two thousand atoms in a fraction of a second. By using a special device that shapes light into a hologram, they created a system capable of transporting atoms in all three dimensions—up, down, and sideways—simultaneously. The key to their success was discovering that they did not need to wait for the light-shaping device to fully settle into a new position before sending the next command. By pushing the device to its limits and updating the light pattern much faster than previously thought possible, they were able to triple the speed at which atoms could be moved without losing them.

The researchers used a device called a spatial light modulator, which acts like a digital mask that can bend laser light into specific shapes. By projecting these shapes, they created thousands of tiny traps, known as optical tweezers, that could hold individual atoms of ytterbium in place. The goal was to take a random collection of atoms and sort them into a perfect, organized lattice. To do this, the team had to generate a new hologram for every step of the journey, telling each atom where to go next. Traditionally, scientists believed they had to wait for the liquid crystals inside the light-shaping device to fully stabilize before issuing the next command, a process that took about 1.6 milliseconds. Waiting for this stability was seen as necessary to ensure the atoms remained trapped.

However, the team decided to test what would happen if they ignored this waiting period. They commanded the device to change the light pattern every 0.7 milliseconds, a time so short that the liquid crystals were still in the middle of moving when the next instruction arrived. Surprisingly, the atoms did not escape. While the researchers observed that the atoms could tolerate slightly smaller steps when the updates were this fast, the overall speed of the transport increased dramatically. By taking more frequent, smaller steps, they moved the atoms three times faster than the traditional method allowed. This finding overturned the assumption that waiting for the device to settle was essential for survival, proving that the atoms could follow the moving traps even while the light field was still in flux.

To make this rapid movement work, the team also had to solve a computational problem. Generating the complex light patterns needed to move thousands of atoms usually takes time, often requiring powerful artificial intelligence models that must be trained on vast amounts of data. The researchers developed a new mathematical approach that could generate these patterns in real time without any training. This method, which they called a warm-start algorithm, used the previous light pattern as a starting point for the next one, allowing it to converge on the correct solution in just a few steps. This eliminated the need for a pre-trained computer model, making the system more flexible and easier to adapt to different arrangements.

Combining these techniques, the team successfully assembled a massive array of 2,078 atoms into a specific geometric pattern known as a kagome lattice, achieving a success rate of 99 percent. This means that out of every thousand spots in the grid, only about ten were empty or occupied by the wrong number of atoms. Beyond just arranging them in a flat sheet, they demonstrated the ability to move atoms between different layers, lifting some atoms up to a second plane and arranging them into new shapes. This three-dimensional control is crucial for future quantum computers, which may need to stack different types of processing zones on top of one another.

The implications of this work extend beyond just moving atoms faster. By showing that liquid crystal devices can be driven much harder than previously thought, the researchers have opened the door to larger and more complex quantum simulations. They demonstrated that their approach can be adapted to existing experimental setups without requiring new hardware, suggesting that other labs could quickly adopt these methods. The ability to rearrange thousands of atoms with such precision and speed brings the vision of large-scale quantum simulators closer to reality, offering a powerful new tool for studying materials and physics that are currently impossible to explore. The work stands as a clear demonstration that by carefully understanding the limits of the tools we use, we can push them further than intuition suggests, unlocking new capabilities in the control of the quantum world.