The substrate is composed of a 100nm thick low-stress SiN layer on top of a Si wafer.The Cooper-Pair Box (CPB) is patterned using electron-beam lithography and double-angle evaporation of aluminum. 31 The thickness of the island and the ground leads are ~ 60 nm and ~ 20 nm respectively. The island is coupled to the ground leads via two small (~ 100 x 100 nm 2 ) Al/AlO x /Al Josephson tunnel junctions, and is arranged in a DC-SQUID configuration.The aluminum layer used to define the nanoresonator, and which ultimately serves as the electrode on top of the nanoresonator, is patterned in the same step as the CPB. This layer acts as an etch mask for undercutting the nanoresonator. To protect the CPB during etching, a layer of PMMA is spun on the sample, and a small window defining the nanoresonator is opened using a second e-beam lithography step. The nanoresonator is then undercut in an ECR etcher with Ar/NF3 plasma: The first step is an anisotropic SiN etch that defines the resonator beam; and the second is an isotropic etch of the underlying Si to undercut the beam.

We demonstrate a method for fabricating arrays of plasmonic nanoparticles with separations on the order of 1 nm using an angle evaporation technique. Samples fabricated on thin SiN membranes are imaged with high-resolution transmission electron microscopy (HRTEM) to resolve the small separations achieved between nanoparticles. When irradiated with laser light, these nearly touching metal nanoparticles produce extremely high electric field intensities, which result in surface-enhanced Raman spectroscopy (SERS) signals. We quantify these enhancements by depositing a p-aminothiophenol dye molecule on the nanoparticle arrays and spatially mapping their Raman intensities using confocal micro-Raman spectroscopy. Our results show significant enhancement when the incident laser is polarized parallel to the axis of the nanoparticle pairs, whereas no enhancement is observed for the perpendicular polarization. These results demonstrate proof-of-principle of this fabrication technique. Finite difference time domain simulations based on HRTEM images predict an electric field intensity enhancement of 82400 at the center of the nanoparticle pair and an electromagnetic SERS enhancement factor of 10(9)-10(10).

We directly observe low-temperature non-equilibrium quasiparticle tunneling in a pair of charge qubits based on the single Cooper-pair box. We measure even-and oddstate dwell time distributions as a function of temperature, and interpret these results using a kinetic theory. While the even-state lifetime is exponentially distributed, the oddstate distribution is more heavily weighted to short times, implying that odd-to-even tunnel events are not described by a homogenous Poisson process. The mean odd-state dwell time increases sharply at low temperature, which is consistent with quasiparticles tunneling out of the island before reaching thermal equilibrium.

We demonstrate the parametric amplification and noise squeezing of nanomechanical motion utilizing dispersive coupling to a Cooper-pair box qubit. By modulating the qubit bias and resulting mechanical resonance shift, we achieve gain of 30 dB and noise squeezing of 4 dB. This qubit-mediated effect is 3000 times more effective than that resulting from the weak nonlinearity of capacitance to a nearby electrode. This technique may be used to prepare nanomechanical squeezed states.