22pBB-5 Higgs mode in superconducting NbN and manipulation of the order parameter by THz wave

Vimala George

This paper presents a comprehensive theoretical investigation of quantum information storage via the Higgs amplitude mode in superconductors. We propose a novel quantum memory mechanism based on coherent excitation and echo retrieval of the Higgs mode, exploiting the collective nature of the superconducting condensate. Through rigorous theoretical analysis combining time-dependent Ginzburg-Landau theory with quantum master equations, we demonstrate that Higgs mode excitations can store quantum information with coherence times exceeding 100 ns. We derive analytical expressions for storage fidelity as a function of temperature, gap anisotropy, and disorder, achieving theoretical fidelities above 95% for storage times up to 100 ns in clean s-wave superconductors below. Numerical simulations validate our theoretical predictions and reveal optimal parameter regimes for NbN thin films. Our findings establish fundamental bounds on Higgs-based quantum memory and propose experimental protocols compatible with current THz spectroscopy capabilities. This work opens new directions for exploiting collective modes in quantum technologies.

Anonymous, Benjamin James Powell, Thomas M. Stace

J. Stajic

Superconductivity In superconductors, electrons of opposite momenta pair to form a highly correlated state that manages to flow without encountering any resistance. Matsunaga et al. manipulated the wavefunction of these pairs in the superconductor NbN with an electromagnetic pulse that they transmitted through a thin layer of the material (see the Perspective by Pashkin and Leitenstorfer). The superconducting gap, which is the energy needed to break the pairs apart, oscillated at twice the frequency of the pulse's electric field. When they matched this frequency to half the gap, the authors excited a collective mode in the superconductor called the Higgs mode, a relative of the Higgs boson in particle physics. Science , this issue p. [1145][1]; see also p. [1121][2] [1]: /lookup/doi/10.1126/science.1254697 [2]: /lookup/doi/10.1126/science.1257302

Yafis Barlas, Chandra Mohan Varma

Andrei Galiautdinov, John M. Martinis

Chuankun Huang, Martin Mootz, Liang Luo +10 more

Detecting photon echoes from superconducting Higgs modes is challenging due to the necessity of preserving and retrieving phase coherence encoded in multiple Higgs and quasiparticle (QP) excitations. Here, we demonstrate the emergence of a Higgs echo in niobium superconductors. This approach disentangles unique quantum pathways involving the Higgs mode and QP excitations. Using Higgs echo spectroscopy, we also uncover unconventional echo formation caused by inhomogeneous broadening and "soft" QP bands, which dynamically evolve under terahertz (THz) driving. Specifically, THz pulse pairs modulate the superconducting gap, imprinting coherence and forming a temporal "Higgs grating." This grating produces echoes with distinctive characteristics: (i) echo rephasing spectral peaks at superconducting gap frequencies, (ii) asymmetric echo formation delays unlike those observed in atoms or semiconductors, and (iii) negative-time echo signals stemming from Higgs-QP anharmonic interactions. Combined with advanced time-frequency analysis, these findings distinguish Higgs from QP responses and clarify their intricate interactions in THz-driven superconductivity.