E. Farhi^*

• Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

N. Graham^†

• Department of Physics, Middlebury College, Middlebury, Vermont 05753, USA

V. Khemani^‡

• Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA

R. Markov^§

• Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

R. Rosales^∥

• Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

• ^*Electronic address: farhi@mit.edu
• ^†Electronic address: ngraham@middlebury.edu
• ^‡Electronic address: khemani@phys.uconn.edu
• ^§Electronic address: ruza@mit.edu
• ^∥Electronic address: rrr@math.mit.edu