Discovery of an Unconventional Quantum Echo by Interference of Higgs Coherence

TL;DR

This paper uncovers an unconventional quantum echo linked to Higgs coherence in superconductors, revealing unique signatures and potential applications in quantum memory and entanglement.

Contribution

It demonstrates the existence of a novel Higgs-related quantum echo with distinctive spectral and temporal features, expanding understanding of Higgs coherence in quantum systems.

Findings

Higgs echo spectral peaks at forbidden frequencies

Asymmetric delay in echo formation

Negative time signals from Higgs-quasiparticle coupling

Abstract

Nonlinearities in quantum systems are fundamentally characterized by the interplay of phase coherences, their interference, and state transition amplitudes. Yet the question of how quantum coherence and interference manifest in transient, massive Higgs excitations, prevalent within both the quantum vacuum and superconductors, remains elusive. One hallmark example is photon echo, enabled by the generation, preservation, and retrieval of phase coherences amid multiple excitations. Here we reveal an unconventional quantum echo arising from the Higgs coherence in superconductors, and identify distinctive signatures attributed to Higgs anharmonicity. A terahertz pulse-pair modulation of the superconducting gap generates a "time grating" of coherent Higgs population, which scatters echo signals distinct from conventional spin- and photon-echoes in atoms and semiconductors. These manifestations appear as Higgs echo spectral peaks occurring at frequencies forbidden by equilibrium particle-hole symmetry, an asymmetric delay in the echo formation from the dynamics of the "reactive" superconducting state, and negative time signals arising from Higgs-quasiparticle anharmonic coupling. The Higgs interference and anharmonicity control the decoherence of driven superconductivity and may enable applications in quantum memory and entanglement.