Fig. 3: Microwave squeezed state generation and transfer through the cryolink.
From: Cryogenic microwave link for quantum local area networks
a Schematics of the experimental setup in the cryogenic link. Alice employs a flux-driven JPA, which performs squeezing on a weak thermal input state. The resulting squeezed state (red triangle markers) is split at a hybrid ring, which acts as a balanced microwave beam splitter, and the two output modes of the hybrid ring are path-entangled. The output modes (orange square markers) are broadened by weak thermal fluctuations with temperature Tatt incident to the second hybrid ring input port. One of the output modes is kept locally in Alice, while the second mode is transferred over the cryogenic link to Bob (green cross markers). Both modes are reconstructed with joint tomography measurements, and the yellow dots mark the reconstruction points in the Alice and Bob cryostats, respectively. We repeat this experiment for multiple center temperatures of the superconducting cable, from Tcenter = 110 mK up to Tcenter = 1 K. b Wigner function of an exemplary squeezed state at the hybrid ring input for Tcenter = 110 mK. Here, the solid line represents the corresponding 1/e contour, featuring variance squeezing below the vacuum level indicated by the dashed contour. c Wigner function of the respective squeezed state at the hybrid ring output. d Wigner function of the respective transferred squeezed state at the Bob cryostat. e–g Exemplary Wigner functions for the identical sequence of squeezed states as in panels (b–d) for the elevated center temperature, Tcenter = 1 K. h Squeezing levels S of different states as a function of the pump power at the JPA sample holder. The vertical dashed line denotes the exemplary squeezed states that are displayed in panels (b–g), which are labeled by the respective legend symbols. Dotted lines connecting data points are guides to the eye. When not shown, error bars are smaller than the symbol size.
