The Future of Quantum Computing

Supercurrents oscillate with quantum interference in nanojunctions

Mikhail Kalenkov of the I.E.Tamm Department of Theoretical Physics, P.N.Lebedev Physical Institute, and Andrei Zaikin of the same institute, alongside National Research University Higher School of Economics, have demonstrated that superconducting nanojunctions with barrier transmissions slightly below unity exhibit pronounced, coherent oscillations of the supercurrent as a function of the Josephson phase. The researchers derived an effective Hamiltonian to model quantum dynamics, then solved a Schrödinger-like equation to obtain wave functions for Andreev levels and evaluate electric current. This work expands understanding beyond full-transmission junctions, offering insights into systems with diffusive barriers and refining existing models of quantum current flow. Andreev States and Effective Hamiltonian Derivation Researchers Mikhail S. Zaikin of the I.E.Tamm Department of Theoretical Physics, P.N.Lebedev Physical Institute, and National Research University Higher School of Economics, developed this Hamiltonian, which allows for the derivation of a Schrödinger-like equation. This equation reveals the wave functions that describe the behavior of these levels and enables the calculation of electric current flowing through the junction under an applied voltage. The theoretical framework builds upon existing understanding of both full and arbitrary transmissions in superconducting weak links, but specifically addresses a gap in knowledge concerning junctions with barriers just below unity. The researchers formulated a Schrödinger-like equation by substituting into their derived Hamiltonian, yielding a Hermitian effective Hamiltonian, H, with linear terms in χ(t) retained to account for long-term evolution and prevent decoherence. This approach is complementary to, and fully consistent with, the established physical picture of multiple Andreev reflections. The resulting equation allows for the construction of solutions describing the entire phase interval, even in reg