Synopsis: Relaxing the requirements for scalable quantum computing

A rigorous estimate shows that an error correction code for a scalable quantum computer can accommodate error at the 0.1% level—about ten times more tolerant than most other methods.
Synopsis figure

To carry out a long calculation on a quantum computer, some form of error correction is necessary. If the error probability of each logical operation is below what is called the “fault-tolerance” threshold, an error correction procedure will actually remove more errors than it introduces, and the overall failure rate can then be made arbitrarily small. The fault-tolerant threshold is typically quoted as 10-4 or 10-5. This is an extremely stringent tolerance, since it says failure must occur in less than 0.01% of the operations.

A few years ago, Emanuel Knill at NIST in Boulder, Colorado, introduced a different approach to error correction that relied primarily on preparing and verifying a (possibly very large) number of auxiliary qubits, called ancillas, in special states that could be used to diagnose the errors in the computer’s qubits, and replace them if necessary. The most attractive feature of these codes was their large error tolerance, which, based on numerical simulations, Knill estimated to be of the order of 1%.

In a paper appearing in Physical Review A, Panos Aliferis, who is at the IBM Watson Research Center, and John Preskill of the California Institute of Technology, rigorously establish a lower bound for the fault-tolerance threshold for one of Knill’s constructions that has relatively small overhead requirements. Their results indicate that fault-tolerant computation should definitely be possible with this scheme, if the error probability per logical operation does not exceed 0.1%. While lower than Knill’s original numerical estimate, this analytical bound is still at least one order of magnitude larger than was thought possible with other codes and it makes the prospect of scalable quantum computing appear that much more feasible. – Julio Gea-Banacloche


Announcements

More Announcements »

Subject Areas

Quantum Information

Previous Synopsis

Particles and Fields

Building a tower out of the vacuum

Read More »

Next Synopsis

Related Articles

Synopsis: Making Hard Problems for Quantum Computers
Quantum Information

Synopsis: Making Hard Problems for Quantum Computers

Researchers have developed a computer algorithm that doesn’t solve problems but instead creates them for the purpose of evaluating quantum computers. Read More »

Viewpoint: A Bird’s Eye View of Circuit Photons
Quantum Information

Viewpoint: A Bird’s Eye View of Circuit Photons

A scanning probe detects the quantum states of photons in a microwave circuit, providing the information needed for quantum simulations. Read More »

Viewpoint: Hiding a Quantum Cache in Diamonds
Quantum Information

Viewpoint: Hiding a Quantum Cache in Diamonds

Entanglement purification, a vital enabler for practical quantum networks, has been shown to be feasible with secluded nuclear memories in diamond. Read More »

More Articles