Stuttgart Physicists Forced an Electron Into a Circular Orbit 10,000 Times Wider Than Normal and Kept It Stable for 11 Milliseconds, 20 Times Longer Than Ever Before, at Room Temperature With No Liquid Helium.
The team set three records at once for circular Rydberg atoms, giant atoms that are the leading candidates for neutral-atom quantum computers. The trick was two transparent conductive plates that block the room's own microwave glow, an idea from the 1980s.
Physicists at the University of Stuttgart have built the longest-lived, largest and longest-held circular Rydberg atoms ever created, and they did it on an ordinary optical bench at room temperature rather than inside a liquid-helium cryostat. The atoms stayed stable for 11 milliseconds, more than 20 times longer than comparable states in free space, and were held in place by a laser trap for 133 milliseconds. The results, published in Nature Communications, set three international records at once and remove one of the main obstacles to using these giant atoms as the building blocks of quantum computers.
A Rydberg atom is an ordinary atom whose outermost electron has been kicked into an extremely high energy level, so far from the nucleus that the atom swells to thousands of times its normal size. Stuttgart's atoms have electron orbits about 1.1 micrometers across, roughly 10,000 times larger than in a ground-state atom, and can feel each other across gaps of about 5 micrometers, a tenth of the width of a human hair but an enormous distance on atomic scales. That long reach is exactly what quantum computers need: it lets two atoms held in separate laser traps interact on command, which is how neutral-atom machines perform logic operations. Companies and labs including QuEra, Pasqal and Atom Computing have built processors on this principle.
The catch is that Rydberg atoms are fragile. Their electron sits so loosely that the faint microwave glow emitted by every surface at room temperature, the same blackbody radiation that makes a warm object radiate heat, is enough to knock it into a different state or strip it away entirely. Ordinary Rydberg states decay in tens or hundreds of microseconds, and experiments that need them to last longer have had to cool the entire apparatus to a few kelvin with liquid helium. "One major challenge in developing high-performance quantum simulators was that Rydberg atoms are highly sensitive and remain stable for only a short time," said Tilman Pfau, head of Stuttgart's 5th Institute of Physics. "We overcame this challenge and increased the stability of the atoms by a factor of 20."
The team, led by group leader Florian Meinert, did two things. First, they used what physicists call a circular Rydberg state, in which the electron moves in a nearly perfect circular orbit with maximum angular momentum, like a planet on a round path rather than a comet on an elongated one. Circular states have far fewer decay channels than the elongated states normally produced, so they are intrinsically longer-lived. Second, they revived a shielding concept from the 1980s: they placed the atoms between two transparent, electrically conductive plates spaced closely enough that the blackbody microwaves responsible for most of the decay simply cannot exist in the gap, because the plates suppress those wavelengths. "Our results show that extremely long-lived Rydberg atoms are possible even at room temperature," Meinert said. "We have refined a well-known concept in physics for use in modern quantum platforms."
"We set three international records at once: the longest lifetime ever measured for individual Rydberg atoms, the largest controlled circular Rydberg atoms and the longest storage time for such atoms in optical tweezers," Meinert said. Einius Pultinevicius, the doctoral researcher who is first author on the paper, said the records "open up new possibilities for making quantum simulators more powerful, performing more computations and controlling quantum systems with greater precision." A qubit that survives 11 milliseconds can, in principle, undergo thousands of gate operations before it decays, compared with a handful for a conventional Rydberg state.
The Stuttgart group says it now has a globally unique platform for circular Rydberg atoms and plans to use it for quantum simulators, quantum computers and high-precision quantum sensors. Removing the need for cryogenic cooling also matters for scaling: a room-temperature neutral-atom processor is smaller, cheaper and easier to run than one that has to live inside a dilution refrigerator, which is the main practical argument the neutral-atom camp makes against superconducting rivals from Google and IBM.
Originally reported by Phys.org / University of Stuttgart.