Prospects for doubling the range of Advanced LIGO

In the coming years, the gravitational-wave community will be optimizing detector performance to target a variety of astrophysical sources which make competing demands on detector sensitivity in different frequency bands. In this paper we describe a number of technologies that are being developed as anticipated upgrades to the Advanced LIGO detectors and quantify the potential sensitivity improvement they offer. Specifically, we consider squeezed light injection for the reduction of quantum noise, detector design and materials changes which mitigate thermal noise and mirrors with significantly increased mass. We explore how each of these technologies impacts the detection of the most promising gravitational-wave sources and suggest an effective progression of upgrades which culminates in a twofold improvement in broadband sensitivity.