Widely tunable on-chip microwave circulator for superconducting quantum circuits

<p>This thesis develops theory for and experimentally demonstrates a new way to break Lorentz\&nbsp;<span style="font-size: 13px;">reciprocity\textendash\textendashthe symmetry, in an electrical network, under exchange of source and detector. The\&nbsp;</span><span style="font-size: 13px;">approach is based on the sequential application of frequency conversion and delay; as frequency\&nbsp;</span><span style="font-size: 13px;">and time are Fourier duals, these operations do not generally commute. We apply this method in\&nbsp;</span><span style="font-size: 13px;">the construction of an on-chip superconducting microwave circulator, a critical component for the\&nbsp;</span><span style="font-size: 13px;">unidirectional routing of quantum information in superconducting networks. The device requires\&nbsp;</span><span style="font-size: 13px;">neither permanent magnets nor microwave control tones, allowing on-chip integration with other\&nbsp;</span><span style="font-size: 13px;">superconducting circuits without expensive control hardware. Isolation in the device exceeds 20\&nbsp;</span><span style="font-size: 13px;">dB over a bandwidth of tens of MHz, and its insertion loss is small, reaching as low as 0.9 dB at\&nbsp;</span><span style="font-size: 13px;">select operation frequencies. Furthermore, the device is linear with respect to input power for signal\&nbsp;powers up to many hundreds of fW (≈10<sup>3</sup> circulating photons), and the direction of circulation\&nbsp;can be dynamically reconfigured. We demonstrate its tunability with operation at a selection\&nbsp;</span><span style="font-size: 13px;">of frequencies between 4 and 6 GHz. Given the current status of quantum error-correction and\&nbsp;</span><span style="font-size: 13px;">architectures for quantum information processing with superconducting circuits, such scalable nonreciprocal\&nbsp;</span><span style="font-size: 13px;">devices will almost certainly be necessary for construction of a superconducting quantum\&nbsp;</span><span style="font-size: 13px;">computer intended to be more than a proof-of-principle.</span></p>
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University of Colorado Boulder
Boulder, Colorado
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