Quantum Coherence and Phase Transitions in Josephson Junctions

Josephson junctions, comprising two superconducting electrodes separated by a thin insulating barrier, underpin a broad range of quantum technologies. The coherent tunnelling of Cooper pairs across the junction manifests as a supercurrent whose magnitude and phase relationship are governed by the Josephson equations. Quantum coherence in these devices is profoundly influenced by the electromagnetic environment, leading to regimes in which phase fluctuations compete with charging effects. When dissipative coupling or Coulomb interactions dominate, the system may undergo a superconductor–insulator transition, suppressing DC supercurrents and giving rise to Coulomb blockade. Conversely, at high frequencies or under tailored driving, coherent behaviour persists through phenomena such as Bloch oscillations, dual Shapiro steps and finite-frequency inductive responses. Advances in high-impedance resonators, multimode environments and thermal probing have revealed rich phase diagrams, including emergent critical points unanticipated in simpler circuit models. These developments illuminate fundamental aspects of many-body quantum dynamics and pave the way for applications in quantum metrology, qubit design and the simulation of complex condensed-matter phenomena.

Research from Nature Portfolio

Recent studies have shed new light on the interplay between dissipation and coherence in single junctions embedded in resistive or multimode environments. Using a bolometric approach, investigators have demonstrated that although DC charge transport may exhibit full Coulomb blockade, high-frequency heat transport measurements reveal a surviving inductive response, indicating that supercurrents endure in the presence of strong phase noise. In parallel, experiments synchronising Bloch oscillations to microwave drives have realised dual Shapiro steps, confirming the fundamental current–frequency relation I = 2ef and offering a pathway to a quantum standard of current based on well-controlled Josephson circuits. Further work with high-impedance multimode resonators has uncovered an emergent quantum phase transition: when the environmental impedance exceeds the resistance quantum, the junction’s effective charging energy becomes dominant beyond a critical mode number, and a level anticrossing in excited states drives a transition with universal spectral signatures. These findings collectively underscore the delicate balance between charging, Josephson and environmental energies in determining the phase of a junction.

Quantum Coherence and Phase Transitions in Josephson Junctions publication trend

The graph below shows the total number of articles in quantum coherence and phase transitions in josephson junctions across all publications each year (not limited to Nature Index journals).

Technical terms

Josephson junction: A superconducting weak link in which Cooper pairs tunnel coherently across an insulating barrier, characterised by a phase-dependent supercurrent.

Quantum coherence: The preservation of a well-defined phase relationship between quantum states, enabling interference and entanglement.

Superconductor–insulator transition: A quantum phase transition in which increasing dissipation or charging energy drives a superconducting system into an insulating regime.

Coulomb blockade: Suppression of charge transport at low bias due to the energy cost of adding individual Cooper pairs to a small superconducting island.

Quantum phase slip: A tunnelling event in which the superconducting phase across a junction changes by 2π, dual to Cooper-pair tunnelling.

References

1. Bolometric detection of Josephson inductance in a highly resistive environment. Nature Communications (2023).
2. Inelastic Decay from Integrability. PRX Quantum (2024).
3. Compact description of quantum phase slip junctions. npj Quantum Information (2023).
4. Absence of a Dissipative Quantum Phase Transition in Josephson Junctions. Physical Review X (2020).
5. Demonstration of dual Shapiro steps in small Josephson junctions. Nature Communications (2024).
6. Emergent quantum phase transition of a Josephson junction coupled to a high-impedance multimode resonator. Nature Communications (2024).