Natural or background radiation is produced by various sources, both natural and artificial. Cosmic rays produce natural radiation, for instance, and so do concrete buildings. It is surrounding us all the time, and so this poses something of an issue for future quantum computers.
Radiation is a Key Hindrance
After numerous experiments that modified the level of natural radiation around qubits, physicists could establish that this background noise does indeed push qubits off balance in a way that hinders them from operating properly.
“Our study is the first to show clearly that low-level ionizing radiation in the environment degrades the performance of superconducting qubits,” says physicist John Orrell, from the Pacific Northwest National Laboratory (PNNL). “These findings suggest that radiation shielding will be necessary to attain long-sought performance in quantum computers of this design.”
Natural radiation is under no circumstance the most important or the only menace to qubit stability, which is basically known as coherence; everything from temperature variations to electromagnetic fields is able to mess with the qubit.
However, scientists say if we’re to attain a future where quantum computers are performing most of our advanced computing needs, then this hindrance from natural radiation is going to have to be addressed.
After the team that carried out the study was faced with issues regarding superconducting qubit decoherence, it decided to examine the possible problem with natural radiation. They discovered it breaks up a main quantum binding known as the Cooper pair of electrons.
“The radiation breaks apart matched pairs of electrons that typically carry electric current without resistance in a superconductor,” says physicist Brent VanDevender, from PNNL. “The resistance of those unpaired electrons destroys the delicately prepared state of a qubit.”
What We’re Against
Regular computers can be distorted by the same issues that impact qubits, but quantum states are a lot more delicate and sensitive. One of the reasons that we don’t have authentic full-scale quantum computers at the moment is that there’s no way yet to keep qubits stable for more than a few milliseconds at a time.
If we can develop on that, the benefits when it comes to computing power could be gigantic: while classical computer bits can only be set as 1 or 0, qubits can be set as 1,0, or both at the same time, a state known as superposition.
Researchers have managed to get it happening, but only for a very short period, and in an extremely controlled setting. The good news, however, is that scientists like those at PNNL are dedicated to the challenge of discovering how to make quantum computers a reality, and with the new finding, we know a bit more about what we’ve to overcome.
“Practical quantum computing with these devices will not be possible unless we address the radiation issue,” says VanDevender. “Without mitigation, radiation will limit the coherence time of superconducting qubits to a few milliseconds, which is insufficient for practical quantum computing.”
A paper detailing the research has been published in the journal Nature.