Google uses “magic” to cut quantum computing errors

Google researchers have demonstrated a new way to reduce errors in quantum computing, bringing the company closer to building machines capable of solving practical problems. Tested on the company’s Willow quantum processor, the technique, called “magic state cultivation,” reduced preparation errors by around 40 times and produced quantum states with 99.99 % logical fidelity.

The term “magic states” is an established concept in quantum computing, not a reference to anything supernatural. These states enable quantum computers to perform certain operations needed for universal quantum computing, including those implemented using T gates. Because magic states are consumed during calculations and cannot be reused, producing them reliably at scale is a significant engineering challenge.

Existing methods for producing magic states use a process called magic state distillation, which combines multiple imperfect states to produce a smaller number of more reliable ones. Google says this process can consume a substantial share of a quantum computer's resources, leaving less capacity for actual calculations.

Google's cultivation method takes a different approach. Instead of processing large batches of imperfect states, the system prepares individual states and repeatedly checks them using measurements designed to detect errors without destroying the states being examined. Attempts that fail the checks are discarded, leaving only the most reliable results.

On Google's Willow processor, the technique reduced preparation errors by roughly 40-fold compared with states prepared without cultivation. The resulting states achieved a logical fidelity of 99.99 %, indicating a very low error rate. However, this accuracy came at a cost: in the most stringent experimental runs, around 92 % of attempts were discarded, leaving just 8 % for use.

Measuring such small errors also presented a challenge. The team developed a technique called kickback tomography after discovering that temperature fluctuations and electrical equipment noise were distorting their initial measurements. The researchers then demonstrated that cultivated states could be transferred into a larger quantum error-correction code, although the transfer introduced additional errors.

The experiment does not deliver a complete fault-tolerant quantum computer. Instead, it addresses a specific engineering bottleneck: producing the high-quality states needed for useful calculations without devoting excessive hardware resources to their preparation.

Andrew Sozinow - Tech Writer - 153 articles published on Notebookcheck since 2024

I’ve been fascinated by computers, electronics and modern technology since childhood. I started writing IT-news at high school and have been doing it continuously for more than 10 years. During this time, I have worked for many media outlets, and now I am a news editor at 3DNews. Sometimes I also write smartphone reviews. In July 2024, I decided to try my hand at writing news on Notebookcheck. When I'm not working, I like to play videogames, do puzzles, and travel.