We study voltage response of nano-bridge based DC-SQUID fabricated on a Si_{3}N_{4} membrane. Such a configuration may help in reducing 1/f noise, which originates from substrate fluctuating defects. We find that the poor thermal coupling between the
DC-SQUID and the substrate leads to strong hysteretic response of the SQUID, even though it is biased by an alternating current. In addition, when the DC-SQUID is biased near a threshold of spontaneous oscillations, the measured voltage has an intermittent pattern, which depends on the applied magnetic flux through the SQUID.
We study the metastable response of a highly hysteretic DC-SQUID made of a Niobium loop interrupted by two nano-bridges. We excite the SQUID with an alternating current and with direct magnetic flux, and find different stability zones forming diamond
-like structures in the measured voltage across the SQUID. When such a SQUID is embedded in a transmission line resonator similar diamond structures are observed in the reflection pattern of the resonator. We have calculated the DC-SQUID stability diagram in the plane of the exciting control parameters, both analytically and numerically. In addition, we have obtained numerical simulations of the SQUID equations of motion, taking into account temperature variations and non-sinusoidal current-phase relation of the nano-bridges. Good agreement is found between experimental and theoretical results.
We study self-sustained oscillations (SO) in a Nb superconducting stripline resonators (SSR) integrated with a DC superconducting quantum interface devices (SQUID). We find that both the power threshold where these oscillations start and the oscillat
ions frequency are periodic in the applied magnetic flux threading the SQUID loop. A theoretical model which attributes the SO to a thermal instability in the DC-SQUID yields a good agreement with the experimental results. This flux dependant nonlinearity may be used for quantum state reading of a qubit-SSR integrated device.
Supplementary information for the article Intermode Dephasing in a Superconducting Stripline Resonator (arXiv:0901.3110). The supplementary information is devoted to three main issues. In section I we describe the fabrication process; in section II w
e present the derivation of the Hamiltonian of the system and provide a more detailed discussion about the properties of the microbridges; in section III the hysteretic response of the resonator and the effect of heating are discussed.
We study superconducting stripline resonator (SSR) made of Niobium, which is integrated with a superconducting interference device (SQUID). The large nonlinear inductance of the SQUID gives rise to strong Kerr nonlinearity in the response of the SSR,
which in turn results in strong coupling between different modes of the SSR. We experimentally demonstrate that such intermode coupling gives rise to dephasing of microwave photons. The dephasing rate depends periodically on the external magnetic flux applied to the SQUID, where the largest rate is obtained at half integer values (in units of the flux quantum). To account for our result we compare our findings with theory and find good agreement. Supplementary info at arXiv:0901.3133 .
We utilize a superconducting stripline resonator containing a dc-SQUID as a strong intermodulation amplifier exhibiting a signal gain of 25 dB and a phase modulation of 30 dB. Studying the system response in the time domain near the intermodulation a
mplification threshold reveals a unique noise-induced spikes behavior. We account for this response qualitatively via solving numerically the equations of motion for the integrated system. Furthermore, employing this device as a parametric amplifier yields a gain of 38 dB in the generated side-band signal.
We experimentally and numerically study a NbN superconducting stripline resonator integrated with a microbridge. We find that the response of the system to monochromatic excitation exhibits intermittency, namely, noise-induced jumping between coexist
ing steady-state and limit-cycle responses. A theoretical model that assumes piecewise linear dynamics yields partial agreement with the experimental findings.
We study thermal instability in NbN superconducting stripline resonators. The system exhibits extreme nonlinearity near a bifurcation, which separates a monostable zone and an astable one. The lifetime of the metastable state, which is locally stable
in the monostable zone, is measure near the bifurcation and the results are compared with a theory. Near bifurcation, where the lifetime becomes relatively short, the system exhibits strong amplification of a weak input modulation signal. We find that the frequency bandwidth of this amplification mechanism is limited by the rate of thermal relaxation. When the frequency of the input modulation signal becomes comparable or larger than this rate the response of the system exhibits sub-harmonics of various orders.
We study a novel configuration for displacement detection consisting of a nanomechanical resonator coupled to both, a radio frequency superconducting interference device (RF SQUID) and to a superconducting stripline resonator. We employ an adiabatic
approximation and rotating wave approximation and calculate the displacement sensitivity. We study the performance of such a displacement detector when the stripline resonator is driven into a region of nonlinear oscillations. In this region the system exhibits noise squeezing in the output signal when homodyne detection is employed for readout. We show that displacement sensitivity of the device in this region may exceed the upper bound imposed upon the sensitivity when operating in the linear region. On the other hand, we find that the high displacement sensitivity is accompanied by a slowing down of the response of the system, resulting in a limited bandwidth.
