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A superconducting 180° hybrid ring coupler for circuit quantum electrodynamics
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Schematic of a 180° hybrid ring. In this configuration, ports 1 and 3 act as input ports, while ports 2 and 4 are output ports. (b) Photograph of a niobium hybrid ring fabricated on a silicon substrate and mounted inside a gold-plated copper box.

Image of FIG. 2.
FIG. 2.

Typical transmission data for hybrid rings on sapphire [panels (a) and (b)] and silicon [panels (c) and (d)] substrates measured at 4.2 K with an input power of −40 dBm. For both materials, we observe a coupling of and an isolation of at least −15 dB within a bandwidth of 2 GHz (gray background) around the center frequency. Note that the different noise levels are not related to the substrate material but are caused by the difference in the measurement protocol: no averaging in (a) and (b); 20 times averaging in (c) and (d). Additionally, in (d) is shown for the same sample after remounting it. While the green curve shows a close-to-ideal spectrum, the red curve shows a hump caused by reflections at the chip-connector contact (cf. Fig. 3). In the coupling spectra of (c), such reflections manifest themselves as an asymmetry. In all measurements, a box resonance at approximate 11 GHz can be seen.

Image of FIG. 3.
FIG. 3.

(a) Expected spatially resolved transmission magnitude at the center frequency where the isolation should reach its minimum. Port 2 is used as input port. (b) Measurement of the integral isolation at 4.2 K with a network vector analyzer attached to the LTLSM apparatus. (c) LTLSM data taken at the hump (6 GHz; color code: transmission magnitude). (d) LTLSM data taken at 4.93 GHz, where the isolation is maximal.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A superconducting 180° hybrid ring coupler for circuit quantum electrodynamics