Scientists face numerous obstacles before quantum computers become reliable enough for users to trust their outputs. Error handling has been notoriously difficult to manage on the sensitive equipment. Computer scientists have recently discovered yet another obstacle that they must overcome in order to deliver the promise quantum computers present to humanity, cosmic rays.
Cosmic rays are high-energy protons and atomic nuclei that move through space at nearly the speed of light. Earth is constantly bombarded with them. In fact, millions of cosmic rays penetrate the human body on a daily basis. Their source, so far, has been found to be stars like our sun as well as super nova’s.
In a paper published to Nature Physics, it’s been revealed that cosmic rays could cause a major problem when they hit an operating quantum CPU.
Researchers, working at Google Quantum AI, discovered that when a cosmic ray hits an operating quantum computer it can result in the formation of a quasiparticle called a phonon.
Phonon’s can disrupt operations of a quantum computer by inverting the quantum state of an entangled set of qubits. Qubits are quantum computer’s versions of bits, ones and zeros.
According to a paper published in Nature cosmic rays and latent radioactivity “can ionize the substrate and induce a burst of quasiparticles that destroys qubit coherence throughout the device.” Coherence is fundamental to a quantum processor’s operation and if it is disturbed it renders all data useless.
Google researchers tested and observed the behavior of a set of 26 qubits that researchers deemed the most reliable. The set was left in an idle state for 100 microseconds. Reliable qubits generally remain in their current state if left undisturbed.
During a confirmed cosmic ray strike, a total of 24 of the 26 qubits were found to erroneously flip to an opposite state, a phenomena that would render the quantum processor’s output useless.
While cosmic ray interference is not a new issue — they can even interfere with traditional computers by messing with its electrical charges — researchers are realizing that quantum processors are much more susceptible to the rays’ influence.
The problem is expected to become more pronounced as a quantum processors’ surface area increases with the addition of more entangled qubits. The higher the surface area on the chip the more opportunities are created for cosmic ray interference.
Scientists, so far, are stumped as to how to compensate for this out-of-this-world phenomena. There is no practical way to reliably block cosmic rays however, there may be some clever workarounds that quantum computer scientists can learn from astronomers who have been dealing with the influence of cosmic rays on their sensitive equipment for some time.
Since astronomers have developed ways to cope with cosmic rays when they impact their astronomical imaging equipment this gives hope to quantum computer scientists that the issue is not insurmountable.