Superconducting Qubits Are Getting Serious

Abstract

Viewpoint: Superconducting Qubits Are Getting Serious Matthias Steffen, IBM T.J. Watson Research Center, Yorktown Heights, NY 10598, USA Published December 5, 2011 | Physics 4, 103 (2011) | DOI: 10.1103/Physics.4.103 When placed inside a 3D electromagnetic cavity, a superconducting qubit can be made potentially more useful because of its large size and long coherence time. Observation of High Coherence in Josephson Junction Qubits Measured in a Three-Dimensional Circuit QED Architecture 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 Phys. Rev. Lett. 107, 240501 (2011) Published December 5, 2011 | PDF (free) +Enlarge image Figure 1 APS/Matthias Steffen Figure 1 Representative evolution of T2 coherence times since the first demonstration of a superconducting qubit in 1999 [3]. While the best coherence times (circles, light blue) are longer than those that are reproducible (circles, dark blue), the overall progress has been remarkable as indicated by the dashed black trend line. The most recent 3D work [1] puts another data point right at the top of the list. The dotted green line indicates the coherence time necessary for fault-tolerant quantum computing, assuming the use of quantum error correcting surface codes and a 30ns two-qubit gate. Bigger is better. Rather interestingly, this mantra appears true for superconducting quantum bits (qubits), which are considered one of the most attractive physical realizations of quantum logic elements for quantum information processing. Reporting in Physical Review Letters, Hanhee Paik, at Yale University, and colleagues demonstrate a novel implementation of a superconducting qubit with dimensions of up to almost 1 millimeter (about a factor of 10–100 larger than typically used), exhibiting some of the longest coherence times measured to date [1]. The results carry with them several important messages. First, the results do not just shed light on which decoherence mechanisms play a limiting role for superconducting qubits, but they also show one that does not: Small Josephson junctions apparently do not pose any limit at this stage in the game—contrary to many expectations. Second, superconducting qubits can now be made with coherence times that approach what is necessary for fault-tolerant quantum computing.