Viewpoint: Superconducting Qubits Are Getting Serious
by Matthias Steffen, December 5, 2011 / Physics 4, 103 (2011)
(The html version of Steffen’s article is a bit mangled at the present time, but you can download (for free) the pdf version and that one is just peachy.)
This excellent article by Herr Doktor Matthias Steffen (at IBM) reviews the following paper by a group of people from Yale Univ.:
Observation of High Coherence in Josephson Junction Qubits Measured in a Three-Dimensional Circuit QED Architecture, by Hanhee Paik, D. I. Schuster, Lev S. Bishop, G. Kirchmair, G. Catelani, A. P. Sears, B. R. Johnson, M. J. Reagor, L. Frunzio, L. I. Glazman, S. M. Girvin, M. H. Devoret, and R. J. Schoelkopf
The first superconducting qubit, built in 1999, had decoherence times of about 1 nanosecond. The Yale group has demonstrated superconducting qubits with relaxation times T1 = 60 μs and dephasing times T2 = 20 μs. That’s an improvement by a factor of 10,000 in ten years! Mamma Mia! Hot Dog! (Gate model-) quantum computers are so close, I can taste them!
Compare this to the decoherence times of 4 μs for the resonators of UCSB’s von Neumann architecture which I described in a previous blog post (in English, in Spanish ). The Yale qubits are bigger than the UCSB ones and they are enclosed in a 3 dimensional cavity. (See original Yale paper for a picture of their setup with dimensions indicated.)
Steffen estimates that the new Yale decoherence times slightly surpass what is needed for doing quantum error correction. And he believes that there is still plenty of room for improvement. It appears that no fundamental roadblocks have been encountered yet, although the sources and mechanisms of decoherence are still not well understood.
P.S. The “Viewpoint” articles of the APS (American Physical Society) are one of my favorite online overviews of leading edge physics. They are carefully written by an expert in the field. They contain references to the original papers. They are broader, briefer and less technical than the original papers. But they are much more technical, accurate and detailed than the garbage one reads in most university press releases or popular science articles. Plus they are freely available on the Internet. I’d like to congratulate APS for a brilliant idea, and I hope that for a very long time, they continue to perform this service which is so valuable to science.