30 research outputs found
Stochastic Resonance with a Single Metastable State
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
Observation of Bifurcations and Hysteresis in Nonlinear NbN Superconducting Microwave Resonators
In this paper we report some extraordinary nonlinear dynamics measured in the
resonance curve of NbN superconducting stripline microwave resonators. Among
the nonlinearities observed: aburpt bifurcations in the resonance response at
relatively low input powers, asymmetric resonances, multiple jumps within the
resonance band, resonance frequency drift, frequency hysteresis, hysteresis
loops changing direction and critical coupling phenomenon. Weak links in the
NbN grain structure are hypothesized as the source of the nonlinearities.Comment: This work has been submitted to the IEEE for possible publicatio
Josephson Amplifier for Qubit Readout
We report on measurements of a Josephson amplifier (J-amp) suitable for
quantum-state qubit readout in the microwave domain. It consists of two
microstrip resonators which intersect at a Josephson ring modulator. A maximum
gain of about 20 dB, a bandwidth of 9 MHz, and a center-frequency tunability of
about 60 MHz with gain in excess of 10 dB have been attained for idler and
signal of frequencies 6.4 GHz and 8.1 GHz, in accordance with theory. Maximum
input power measurements of the J-amp show a relatively good agreement with
theoretical prediction. We discuss how the amplifier characteristics can be
improved.Comment: 9 pages, 4 figure
Quantum Nondemolition Measurement of Discrete Fock States of a Nanomechanical Resonator
We study theoretically a radio frequency superconducting interference device
integrated with both a nanomechanical resonator and an LC one. By applying
adiabatic and rotating wave approximations, we obtain an effective Hamiltonian
that governs the dynamics of the mechanical and LC resonators. Nonlinear terms
in this Hamiltonian can be exploited for performing a quantum nondemolition
measurement of Fock states of the nanomechanical resonator. We address the
feasibility of experimental implementation and show that the nonlinear coupling
can be made sufficiently strong to allow the detection of discrete mechanical
Fock states