Fig. 1: The differentially driven SQUID as a parity-protected converter.
From: High-fidelity parametric beamsplitting with a parity-protected converter
a The symmetric DC-SQUID contains two orthogonal modes57,58, the common mode (coupler) and the differential mode (actuator). We selectively couple the former to two bosonic modes and the latter to the drives to take advantage of the natural symmetries of the Hamiltonian in Eq. (1). b Implementing the purely differential drive through a 3D buffer post-cavity (figure is exaggerated for illustrative purposes). The natural separation in electric and magnetic fields in the λ/4 mode is used to purely drive the actuator, without exciting the coupler. The sensitive quantum information is stored in two high-Q λ/4 post-cavities (Alice and Bob) that participate in the coupler, enabling parametric beamsplitting between them. The inset shows an optical micrograph of the SQUID device, displaying the purposely offset antenna pad that counters residual drive-asymmetry. c Frequency stack for relevant modes in the system. The difference of the two drive frequencies (Δd) is fixed to be equal to the cavity detuning (Δab) for resonant beamsplitting. The drives are placed symmetrically around the buffer mode resonance, which is engineered to be far-red detuned from the coupler frequency.
