Researchers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, have shown that they have a functional capability that can drastically speed up the testing of qubits. What used to take days or even weeks can now be completed in a matter of minutes.
By using the Laboratory’s Linear Accelerator Facility to simulate cosmic rays, APL scientists are able to study qubits at a radically accelerated pace compared to standard methods. Image Credit: Johns Hopkins APL/Craig Weiman
A concerning and recurrent issue has surfaced as the capacity of quantum computers based on superconducting qubits has grown in recent years: the propensity for numerous qubits to abruptly and mysteriously fail all at once for a short time. In a catastrophic failure, the quantum computer essentially stops functioning as a quantum computer.
Initially, experts believed that ambient radiation was responsible for these spontaneous qubit collapses. Ambient radiation originates from sources like muons, which are generated when high-energy cosmic rays collide with atoms in the upper atmosphere, and terrestrial gamma rays, emitted by rock, soil, and even concrete.
Terrestrial radiation is common, well-known, and simple to protect against, but there has not been enough research done on how cosmic radiation affects quantum systems. Such research is difficult because the high-energy impact events that scientists need to see happen at unpredictable intervals, seconds or even minutes apart.
As superconducting quantum computing chips continue to increase in size, and as the algorithms increase in complexity, the sorts of ‘computer crashes’ generated by cosmic ray muons could become a true roadblock.
Joan Hoffmann, Mission Area Executive, Research and Exploratory Development, Johns Hopkins Applied Physics Laboratory
Up until now, researchers have used underground shielded cryogenic refrigeration systems, or “fridges,” with detectors underneath them, to study cosmic radiation by placing quantum chips inside and waiting for cosmic rays to strike. Since impact events are still unpredictable and relatively rare, attempts to increase their frequency by placing a radiation source near the refrigerators are not very useful.
However, Assistant Program Manager of Alternative Computing Paradigms Kevin Schultz said there is a better way. Electrons can be driven to energy levels that mimic cosmic ray muons using a linear accelerator at APL. This implies that APL scientists can actively create cosmic rays rather than passively waiting for them to strike.
The usual method for collecting data takes days or even weeks. We can reproduce those results in a matter of minutes. And we do not have to comb through our data to identify impact events, because we are producing the events ourselves.
Kevin Schultz, Assistant Program Manager, Johns Hopkins Applied Physics Laboratory
To test the effects of radiation on superconducting qubit chips, Schultz and the other members of the APL team, including lead scientists Alan Hunt, Tom McJunkin, and Tom Haard, have shown that the linear accelerator can be used to simulate both cosmic rays and terrestrial gamma radiation.
During the 2024 Radiation Impact on Superconducting Qubits workshop at Fermi National Accelerator Laboratory in Batavia, Illinois, McJunkin gave a detailed presentation of APL's verified results.
According to Schultz, the team hopes to collaborate with other members of the research community to advance the field as this capability opens up new areas of study into how radiation affects qubit devices.
We have effectively replicated everything that anyone else has ever done, and we are ready to do more. As other groups develop solutions to this problem, we have a rapid and reliable means to test those solutions.
Kevin Schultz, Assistant Program Manager, Johns Hopkins Applied Physics Laboratory