Error-free quantum computer or reality

2022-05-26 09: 48 Source: Science and Technology Daily

According to a paper published in the journal Nature on 25th, a team led by Thomas Muntz of the Department of Experimental Physics at Innsbruck University in Austria, Marcus Mü ller of Aachen University of Technology in Germany and Ulrich Research Center in Germany demonstrated the basic building blocks of fault-tolerant quantum computing, and successfully realized a set of computing operations on two logical qubits for the first time, which can be used to realize any possible operation, meaning that error-free quantum computers will become a reality.

Quantum computers are inherently more susceptible to interference from the environment, so error correction mechanisms may always be needed, otherwise errors will spread uncontrollably in the system and information will be lost. Quantum no-cloning theorem shows that it is impossible to copy any unknown quantum state exactly. Therefore, redundancy can be achieved by distributing logical quantum information to entangled states of multiple physical systems, such as multiple individual atoms.

Inbruck experimental physicist Lucas Bosler explained, "For quantum computers in the real world, we need a set of universal doors with which we can program all algorithms."

The research team realized this universal gate set on an ion trap quantum computer with 16 trapped atoms. Quantum information is stored in two logical qubits, each qubit distributed on seven atoms.

Now, for the first time, researchers can implement two computational gates on these fault-tolerant qubits, which are necessary for the general gate set: a gate that acts on two qubits (a control-NOT gate) and a logical T gate, which is particularly difficult to implement on fault-tolerant qubits.

Physicists demonstrated the T-gate by preparing a special state in a logical qubit and transmitting it to another qubit through entanglement gate operation.

In the coded logical qubits, the stored quantum information is protected from errors. But if there are no calculation operations, it is useless, and these operations themselves are prone to errors. Therefore, the researchers manipulated the logical qubits, so that the errors caused by the underlying physical operations can be detected and corrected. Therefore, they implemented the fault-tolerant implementation of the first universal gate set on the coded logical qubits.

The implementation of fault tolerance requires more operations than non-fault tolerance. This will introduce more errors on the scale of a single atom. And the workload and complexity are increased, but the quality produced is better. Researchers also use numerical simulations on classic computers to check and confirm their experimental results.

Researchers have demonstrated all the foundations of fault-tolerant computing on quantum computers. Now the task is to implement these methods on larger and more useful quantum computers. This method demonstrated on the ion trap quantum computer can also be used in other quantum computer architectures.

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