Listening for new physics with quantum acoustics

We present a novel application of a qubit-coupled phonon detector to search for new physics, e.g., ultralight dark matter (DM) and high-frequency gravitational waves. The detector, motivated by recent advances in quantum acoustics, is composed of superconducting transmon qubits coupled to high-overtone bulk acoustic resonators ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>h</a:mi> <a:mi>BARs</a:mi> </a:mrow> </a:math> ) and operates in the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mtext> </c:mtext> <c:mi>GHz</c:mi> <c:mo>−</c:mo> <c:mn>10</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:mi>GHz</c:mi> </c:mrow> </c:math> frequency range. New physics can excite <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi mathvariant="script">O</e:mi> <e:mo stretchy="false">(</e:mo> <e:mn>10</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:mi mathvariant="normal">μ</e:mi> <e:mi>eV</e:mi> <e:mo stretchy="false">)</e:mo> </e:math> phonons within the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>h</k:mi> <k:mi>BAR</k:mi> </k:math> , which are then converted to qubit excitations via a transducer. We detail the design, operation, backgrounds, and expected sensitivity of a prototype detector, as well as a next-generation detector optimized for new physics signals. We find that a future detector can complement current haloscope experiments in the search for both dark photon DM and high-frequency gravitational waves. Lastly, we comment on such a detector’s ability to operate as a <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mrow> <m:mi mathvariant="script">O</m:mi> <m:mo stretchy="false">(</m:mo> <m:mn>10</m:mn> <m:mtext> </m:mtext> <m:mtext> </m:mtext> <m:mi mathvariant="normal">μ</m:mi> <m:mi>eV</m:mi> <m:mo stretchy="false">)</m:mo> </m:mrow> </m:math> athermal phonon sensor for sub-GeV DM detection.