A novel search for high-frequency gravitational waves with low-mass axion haloscopes

Gravitational waves (GWs) generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. We discuss this phenomenon with a particular focus on reinterpreting the results of axion haloscopes based on lumped-element detectors, which probe GWs in the 100 kHz–100 MHz range. Measurements from ABRACADABRA and SHAFT already place bounds on GWs, although the present strain sensitivity is weak. However, we demonstrate that the sensitivity scaling with the volume of such instruments is significant—faster than for axions—and so rapid progress will be made in the future. With no modifications, DMRadio-<math display="inline"><mrow><msup><mrow><mi mathvariant="normal">m</mi></mrow><mrow><mn>3</mn></mrow></msup></mrow></math> will have a GW strain sensitivity of <math display="inline"><mrow><mi>h</mi><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>20</mn></mrow></msup></mrow></math> at 200 MHz. A simple modification of the pickup loop used to readout the induced magnetic flux can parametrically enhance the GW sensitivity, particularly at lower frequencies.