We reported a dual-core triple-mode voltage-controlled oscillator (VCO) to adapt to the low power consumption and large frequency tuning range (FTR) of the signal source in quantum interface systems. We proposed using only magnetic and inductive tuning elements for resonance splitting to construct the VCO's triple-mode LC tank. This avoids the FTR sacrifice when using a conventional capacitive tuning element to build the multi-mode tank. To reduce the power consumption of the negative transconductance (-GM) cells in the multicore multi-mode VCO, we proposed a structure that provides a triple oscillating mode with only two -GM cores. In addition, to overcome the deterioration of phase noise (PN) due to the switch-on resistances, we introduced a switching -GM technique for mode selection without using the MOSFET switches. The wideband VCO was specifically designed for cryogenic operation, utilizing a 28 nm CMOS technology. The measured results demonstrate an FTR of 7.1-15.7 GHz (75.4%) and a peak figure-of-merit (FoM) of 202.1 dBc/Hz at 3.7 Kelvin.