Nature Communications 2: Article number: 439 (2011); Published: 23 August 2011; Updated: 27 May 2015

The published version of this article contains two errors. In equation (18), there is a typographical error in the second term; it should read Rcircle2Rbead instead of RcircleRbead2. The corrected version of equation (18) reads as follows:

In addition, the y axis of the plot in Fig. 3f was incorrectly scaled. A corrected version of Fig. 3 is shown below. Neither of these errors affects any of the conclusions in the paper, as all calculations were based on the correct power spectrum and the correct version of equation (18). We apologize for any confusion that these errors might have caused.

Figure 3