Google’s quantum Willow chip may be able to grow ‘magic states’

Google’s quantum Willow chip may enable the creation of "magic states" that improve the accuracy of complex calculations performed by quantum computers. Quantum computers offer exponential computational power through their ability to process multiple possibilities simultaneously, but today's machines are still limited by the frequent errors of their qubits, or quantum bits.

To overcome these errors, quantum computers need to use so-called "magic states," which help reduce errors in calculations. In a study published in Science, researchers from Google Research demonstrate a new technique called "cultivation" that could make magic states more affordable. Traditional computers build calculations using simple logic gates, while quantum computers use "Clifford gates."

However, there is one special gate called a "non-Clifford gate" that unlocks quantum computers' power, and it is created using a magic state. The standard method to make magic states, called "distillation," is expensive and generates fewer, more accurate quantum states from many imperfect ones. The cultivation technique, on the other hand, works on a single state and grows it into a stronger magic state.

In the study, Google’s Willow chip encoded a rough magic state in a few qubits and measured it. States that passed the test were then spread across more qubits for stronger protection. With cultivation, error rates fell by roughly 40-fold compared to without it, using 54 physical qubits out of the chip’s 105. The Google experiment shows that cultivation works in practice, but the technique relies on a quality assurance step that discards 92 percent of attempts.

While the results are still far from what practical applications demand, the work represents a step in the right direction towards achieving near-term scientific applications of quantum computing.