Detecting the Unruh Effect in Superconducting Qubits

Detecting the Unruh effect is a significant challenge in fundamental physics. According to a recent study submitted on December 18, 2025, to the arXiv in the General Relativity and Quantum Cosmology category, researchers have derived a quantitative understanding of the suppression of the Unruh effect when exciting massive fields.

The report notes that this suppression occurs when a field's rest energy is much larger than the acceleration energy scale, specifically when Mc squared is much greater than h-bar a over c. The study presents an exponential suppression factor, approximately equal to the exponential of a constant multiplied by Mc squared over h-bar a over c, which is universal across different frameworks.

For an electron-mass field at achievable accelerations, this suppression exceeds 10 to the power of 9 orders of magnitude, making detection for such fields practically impossible. The authors suggest that to avoid this suppression, the rest energy of the field must be comparable to or less than the acceleration energy scale, which would require unfeasibly high accelerations.

For example, detecting the effect for an electron-mass field would necessitate accelerations exceeding 4.6 times 10 to the power of 29 meters per second squared. While employing a massless field could circumvent this issue, the study proposes engineering a small effective mass that meets the optimal condition where h-bar a over c is significantly greater than the effective mass times c squared.

The research outlines a practical implementation using a superconducting circuit with a Josephson persistent-current qubit, which serves as an analog to a Unruh-DeWitt detector, coupled with a microwave resonator that acts like the scalar field.

The optimal condition for this system is established as 2I sub p times delta Phi being much greater than delta, where I sub p represents the persistent current, delta Phi is the magnetic flux swing, and delta is the qubit's tunneling energy gap.