The authors thank P.J. Duda for fabrication assistance and Y. Lu and S. Chakram for helpful discussions. The authors thank MIT Lincoln Laboratory for providing a travelling-wave parametric amplifier. This effort is supported by the Army Research Office under contract W911NF-15-2-0058. Devices and experiments were also supported by the Air Force Office of Scientific Research, and by the Department of Energy (DOE). K.J.S. was supported by NSF GRFP (NSF DGE-1144085). É.D. was supported by LDRD funds from Argonne National Laboratory. A.N.C. was supported in part by the DOE, Office of Basic Energy Sciences. D.I.S. acknowledges support from the David and Lucile Packard Foundation. This work was partially supported by the UChicago MRSEC (NSF DMR-1420709) and made use of the Pritzker Nanofabrication Facility, which receives support from SHyNE, a node of the National Science Foundation’s National Nanotechnology Coordinated Infrastructure (NSF NNCI-1542205). The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the US Government.