Oren Suchoi

Synchronization in an optomechanical cavity

We study self-excited oscillations (SEO) in an on-fiber optomechanical cavity. Synchronization is observed when the optical power that is injected into the cavity is periodically modulated. A theoretical analysis based on the Fokker-Planck equation evaluates the expected phase space distribution (PSD) of the self-oscillating mechanical resonator. A tomography technique is employed for extracting PSD from the measured reflected optical power. Time-resolved state tomography measurements are performed to study phase diffusion and phase locking of the SEO. The detuning region inside which synchronization occurs is experimentally determined and the results are compared with the theoretical prediction.

Intermodulation and parametric amplification in a superconducting stripline resonator integrated with a dc-SQUID

We utilize a superconducting stripline resonator containing a dc-SQUID as a strong intermodulation amplifier exhibiting a signal gain of 24 dB and a phase modulation of 30 dB. Studying the system response in the time domain near the intermodulation amplification 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 an abrupt rise of 38 dB in the generated side-band signal.

Intermode dephasing in a superconducting stripline resonator

We study a 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 a 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.

Intermittency in an optomechanical cavity near a subcritical Hopf bifurcation

Weexperimentallystudyanoptomechanicalcavityconsistingofanoscillatingmechanicalresonatorembedded in a superconducting microwave transmission line cavity. Tunable optomechanical coupling between the mechanicalresonatorandthemicrowavecavityisintroducedbypositioninganiobium-coatedsingle-modeoptical fiber above the mechanical resonator. The capacitance between the mechanical resonator and the coated fiber gives rise to optomechanical coupling, which can be controlled by varying the fiber-resonator distance. We study radiation-pressure-induced self-excited oscillation as a function of microwave driving parameters (frequency and power). Intermittency between limit-cycle and steady-state behaviors is observed with blue-detuned driving frequency. The experimental results are accounted for by a model that takes into account the Duffing-like nonlinearity of the microwave cavity. A stability analysis reveals a subcritical Hopf bifurcation near the region where intermittency is observed.

Self-oscillations in a superconducting stripline resonator integrated with a dc superconducting quantum interference device

We study self-sustained oscillations in a Nb superconducting stripline resonator integrated with a dc superconducting quantum interference device (SQUID). We find that both the power threshold where these oscillations start and the oscillation frequency are periodic in the applied magnetic flux threading the SQUID loop. A theoretical model which attributes the self-sustained oscillations 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-superconducting resonator integrated device.

Sensing Dispersive and Dissipative Forces by an Optomechanical Cavity

We experimentally study an optomechanical cavity that is formed between a mechanical resonator, which serves as a movable mirror, and a stationary on-fiber dielectric mirror. A significant change in the behavior of the system is observed when the distance between the fibers tip and the mechanical resonator is made smaller than about 1 micrometer. The observed effects are attributed to the combined influence of Casimir force, Coulomb interaction due to trapped charges, and optomechanical coupling. The comparison between experimental results and theory yields a partial agreement.

Tunable strong nonlinearity of a micromechanical beam embedded in a dc-superconducting quantum interference device

We present a study of the controllable nonlinear dynamics of a micromechanical beam coupled to a dc-SQUID (superconducting quantum interference device). The coupling between these systems places the modes of the beam in a highly nonlinear potential, whose shape can be altered by varying the bias current and applied flux of the SQUID. We detect the position of the beam by placing it in an optical cavity, which sets free the SQUID to be used solely for actuation. This enables us to probe the previously unexplored full parameter space of this device. We measure the frequency response of the beam and find that it displays a Duffing oscillator behavior which is periodic in the applied magnetic flux. To account for this, we develop a model based on the standard theory for SQUID dynamics. In addition, with the aim of understanding if the device can reach nonlinearity at the single phonon level, we use this model to show that the responsivity of the current circulating in the SQUID to the position of the beam can become divergent, with its magnitude limited only by noise. This suggests a direction for the generation of macroscopically distinguishable superposition states of the beam.

Metastability in a nanobridge-based hysteretic dc SQUID embedded in a superconducting microwave resonator

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.

Damping in a superconducting mechanical resonator

We study a mechanical resonator made of aluminum near the normal-to-superconducting phase transition. A sharp drop in the rate of mechanical damping is observed below the critical temperature. The experimental results are compared with predictions based on the Bardeen Cooper Schrieffer theory of superconductivity and a fair agreement is obtained.

Cooling to heating transition in an optomechanical cavity

We experimentally study the phase space distribution (PSD) of a mechanical resonator that is simultaneously coupled to two electromagnetic cavities. The first one, operating in the microwave band, is employed for inducing either cooling or self-excited oscillation (SEO), whereas the second one, operating in the optical band, is used for displacement detection. A tomography technique is employed for extracting the PSD from the signal reflected by the optical cavity. We monitor the time evolution of the transitions from an optomechanically cooled state to a state of SEO. This transition is induced by abruptly switching the microwave driving frequency from the red-detuned region to the blue-detuned one. The experimental results are compared with theoretical predictions that are obtained by numerically integrating the Fokker-Planck equation. The feasibility of generating quantum superposition states in the system under study is briefly discussed.