We show that high harmonic generation (HHG) in carbon nanotubes (CNTs) can be efficiently controlled using the Aharonov-Bohm (AB) effect. When a static magnetic field ($B$) is applied along the tube, electronic wave functions acquire complex phases along the circumferential direction (the AB effect), which modifies the band structure. When the magnetic field is applied to metallic CNTs, which can be regarded as one-dimensional massless Dirac systems, realistic values of $B$ lead to a nonzero gap in the THz regime. We demonstrate that such a change from gapless to gapped Dirac systems drastically increases the HHG intensity in the THz regime. In the gapless Dirac system, the velocity of each electron never changes under the electric field, and thus there is no HHG. On the other hand, the gap opening activates both the interband and intraband currents, which strongly contribute to HHG. Our work demonstrates a unique way to manipulate HHG in nanotubes by tuning electronic wave functions using the magnetic field and the tube structure.

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• High-order harmonic generation
• Nonlinear optics
• Graphene
• Nanotubes
• Nonequilibrium systems
• Density matrix methods
• Terahertz sources
• Tight-binding model