Wisconsin Quantum Institute

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SQUID-Based Broadband Microwave Isolator
Date: Thursday, May 4th
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Matt Beck, IBM Yorktown Heights
Abstract: As superconducting quantum processors grow in size and complexity, so must the peripheral hardware required for the control and readout of such processors. One singular piece of hardware common to superconducting quantum processors setups is the microwave isolator. Current microwave isolator technology can be generally understood in the context of timereversal symmetry breaking via the use of ferrite materials. While generally exhibiting wide (> GHz) bandwidths and large (>20 dB) directionality, these ferrite-based devices are physically large with volumes exceeding 15 cm^3. These devices can also introduce uncontrolled magnetic fields at or near the quantum processor resulting in deleterious effects such as frequency shifts, excess flux noise, or flux vortex formation. For quantum processors at scale to achieve quantum advantage, a replacement must be found. In this talk, I will describe work towards the realization of a superconducting broadband microwave isolator utilizing DC-SQUIDs. I will detail how, with appropriate application of microwave flux drives, the non-linear inductance of the SQUIDs allows for power at the signal frequency travelling in the forward direction to be three-wave mixed and back resulting in constructive interference and near unity transmission. I will also show how, in the reverse direction, the same mixing process results in destructive interference and thus suppression of the signal frequency. Data will be presented on a variety of nanofabricated devices. The data show excellent model-hardware correlation where directionality greater than 15 dB at bandwidths approaching 700 MHz with minimal added insertion loss is achieved. Finally, further extensions of the work will be discussed on how to achieve commercial levels of isolation and the realization of a fully superconducting replacement of commercial ferrite isolators.
Host: Robert McDermott
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