June 2, 2014 (HP78).  Papers [1] and [2] describe progress in demonstrating the effectiveness the surface code method of quantum error correction for logic gates involving superconducting qubits.   Generally, the fidelity threshold should be better than 99% for such methods to be applicable.  In particular John Martinis’s group at University of Califonia, Santa Barbara (UCSB), and external collaborators demonstrated two qubit gate fidelity of up to 99.4 % [1].  Their quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbor coupling. As a further demonstration, they constructed a five-qubit complete circuit and full set of gates. They claim to have demonstrated that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.

 

IEEE Spectrum, the popular IEEE magazine for that Institute members, published recently an article “Amazingly Accurate Quantum Computing” by Jeremy Hsu, which in the free-access online form released on May 26, 2014, has the title “Error Correction Moves Quantum Computing Closer to Reality”.   It is based on references cited above.

 

References

[1] R. Barends et al., Nature 508, 500-503 (2014), doi:10.1038/nature13171.

[2] Jerry M. Chow et al., arXiv:1311.6330 [quant-ph]