Josephson's effect in the Schwarzschild background

TL;DR

This paper develops a covariant framework for Josephson effects in curved spacetimes, specifically Schwarzschild, revealing how gravity influences phase dynamics, critical currents, and interference patterns in superconducting systems.

Contribution

It introduces a gauge-invariant, analytic approach to Josephson phenomena in static curved backgrounds, deriving redshifted laws and analyzing gravitational effects on superconducting transport.

Findings

Redshifted AC Josephson law relates phase evolution to gravitational potential.

Critical currents scale with gravitational redshift factor, $ ightarrow ext{I}_{c, ext{infinity}} ext{ } ext{propto} ext{ } ext{ extalpha} ext{ } ext{I}_c^{ ext{proper}}$.

Gravity does not shift the interference pattern at linear order but causes small envelope deformations.

Abstract

We develop a fully covariant, analytic framework for Josephson phenomena in static curved spacetimes and specialize it to the Schwarzschild exterior. The formulation rests on two invariant elements: the gauge-invariant condensate momentum that governs phase dynamics and the conserved current whose hypersurface flux encodes transport for an observer at infinity. Using the timelike Killing field to relate proper and asymptotic quantities, we derive a redshifted AC Josephson law in which the asymptotic phase-evolution rate is proportional to the difference of redshifted voltage drops, i.e. to $V_i^\infty \equiv \alpha_i V_i^{\rm proper}$; equivalently, it depends on $\alpha_i V_i^{\rm proper}$ for local control. Under RF drive specified at infinity, the Shapiro-step loci are invariant (expressed in asymptotic voltages) while propagation phases set any apparent lobe translation. For DC transport, a short-junction solution on a static slice yields the proper current-phase relation; mapping to asymptotic observables gives a single-power redshift scaling of critical currents, $I_{c,\infty}\propto \alpha I_c^{\rm proper}$, whereas power scales as $P_\infty\propto \alpha^2 P_{\rm proper}$. In a "vertical" dc-SQUID with junctions at different radii, gravity does not shift the DC interference pattern at linear order; it produces a small envelope deformation and an amplitude rescaling. Gravity does not alter the local Josephson microphysics; it reshapes the clocks and energy accounting that define measurements at infinity. The resulting predictions are gauge- and coordinate-invariant, operationally stated in terms of an experimenter who can control (proper vs. asymptotic bias), and remain analytic from the weak-field regime to the near-horizon limit.