We consider a quarter wave coplanar microwave cavity terminated to ground via asuperconducting quantum interference device. By modulating the flux through the loop,the cavity frequency is modulated. The flux is varied at twice the cavity frequencyimplementing a parametric driving of the cavity field. The cavity field also exhibitsa large effective nonlinear susceptibility modelled as an effective Kerrnonlinearity, and is also driven by a detuned linear drive. We show that thesemi-classical model corresponding to this system exhibits a fixed point bifurcationat a particular threshold of parametric pumping power. We show the quantum signatureof this bifurcation in the dissipative quantum system. We further linearise about thebelow threshold classical steady state and consider it to act as a bifurcationamplifier, calculating gain and noise spectra for the corresponding small signalregime. Furthermore, we use a phase space technique to analytically solve for theexact quantum steady state. We use this solution to calculate the exact small signalgain of the amplifier.
We give a semiclassical analysis of the average photon number as well as photon number variance (Fano factor
F) for a Josephson junction (JJ) embedded microwave cavity system, where the JJ is subject to a fluctuating (i.e., noisy) bias voltage with finite dc average. Through the ac Josephson effect, the dc voltage bias drives the effectively nonlinear microwave cavity mode into an amplitude squeezed state
(F<1), as has been established previously [Armour et al., Phys. Rev. Lett. 111, 247001 (2013)], but bias noise acts to degrade this squeezing. We find that the sensitivity of the Fano factor to bias voltage noise depends qualitatively on which stable fixed point regime the system is in for the corresponding classical nonlinear steady-state dynamics. Furthermore, we show that the impact of voltage bias noise is most significant when the cavity is excited to states with large average photon number.
Abstract We show how robust magnon-magnon (or photon-magnon) entanglement and asymmetric quantum steering can be achieved in a nonlinear cavity-magnon system composed of a microwave cavity and two yttrium-iron-garnet (YIG) spheres, which are each driven by external microwave driving fields. The self-Kerr nonlinearity (SKN) of two magnons drives this behaviour and we study how two-fold periodically-modulated driving fields influence the system dynamics. We find that beating occurs both in the classical average of the cavity mode and in the entanglement between modes. Moreover, the use of modulated driving fields can enhance the degree of entanglement generated as well as giving rise to asymmetric quantum steering effects that would not otherwise be present. Finally, we show that the entanglement generated this way has improved robustness to thermal noise opening the way to potential applications of magnon-based hybrid systems in quantum information processing and studies of fundamental physics.