Quantum computers always require error correction mechanisms as they are more susceptible to disturbances. Redundancy can be achieved by dispersing logical quantum information into an entangled state of different physical systems, such as multiple individual atoms because quantum physics’s fundamental laws prohibit copying quantum information.
Now, a team of scientists has, for the first time, successfully realized a set of computational operations on two logical qubits.
A universal set of gates is required for a real-world quantum computer. Through these gates, one can program all algorithms.
Scientists implemented this universal set of gates on an ion-trap quantum computer featuring 16 trapped atoms. The quantum information was stored in two logical quantum bits, each distributed over seven atoms. Now, for the first time, it has been possible to implement two computational gates on these fault-tolerant quantum bits, which are necessary for a universal set of gates: a computational operation on two quantum bits (a CNOT gate) and a logical T gate, which is particularly difficult to implement on fault-tolerant quantum bits.
By generating a specific state in a logical quantum bit and teleporting it to another quantum bit via an entangled gate operation, the physicists demonstrated the T-gate.
Scientists implemented operations on the logical qubits so that errors caused by the underlying physical processes could also be detected and corrected. Hence, they have implemented the first fault-tolerant implementation of a universal set of gates on encoded logical quantum bits.
Thomas Monz of the Department of Experimental Physics at the University of Innsbruck said, “The fault-tolerant implementation requires more than non-fault-tolerant operations. This will introduce more errors on the scale of single atoms, but the experimental operations on the logical qubits are better than non-fault-tolerant logical operations. The effort and complexity increase, but the resulting quality is better.”
By using numerical simulations on classical computers, scientists confirmed the results. They demonstrated all the building blocks for fault-tolerant computing on a quantum computer. The task now is to implement these methods on larger and more useful quantum computers. The methods demonstrated in Innsbruck on an ion-trap quantum computer can also be used on other architectures for quantum computers.
- Poster, L., Heuβen, S., Pogorelov, I. et al. Demonstration of fault-tolerant universal quantum gate operations. Nature 605, 675–680 (2022). DOI: 10.1038/s41586-022-04721-1