Physicists at the National Institute of Standards and Technology (NIST) have achieved a record low probability of error in quantum information processing with a single quantum bit (qubit): 1 per 50,000 logic operations.

This is the first published error rate small enough to meet theoretical requirements for building viable quantum computers.

The NIST experiment with a single beryllium ion qubit is a milestone for simple quantum logic operations, the researchers said. However, a working quantum computer also will require two-qubit logic operations with comparably low error rates.

One error per 10,000 logic operations is a commonly agreed upon target for a low enough error rate to use error correction protocols in a quantum computer, the physicists said.

The record low error rate was made possible by two major changes in the group’s experimental setup. First, scientists manipulated the ion using microwaves instead of the usual laser beams. A microwave antenna was incorporated into the ion trap, with the ion held close by, hovering 40 micrometers above the trap surface. The use of microwaves reduced errors caused by instability in laser beam pointing and power, as well as spontaneous ion emissions.

Second, the ion trap was placed inside a copper vacuum chamber and cooled to 4.2 K with a helium bath to reduce errors caused by magnetic field fluctuations in the lab.

Ref.: K.R. Brown, et al., Single-qubit gate error below 10-4 in a trapped ion, Physical Review A, 2011; (in press) [link]