We study the thermodynamic liquid-gas transition and coexistence (LGTC) for ground-state bosons under contact interactions. We find that the LGTC can be facilitated by the mismatch of spin polarization, dubbed “spin twist,” between single-particle and interaction channels of bosons with spin degrees of freedom. Such a spin twist uniquely stabilizes the gas phase by creating an effective repulsion for low-density bosons, thereby enabling LGTC in the presence of a quantum droplet at a much larger density. We have demonstrated the scheme for binary bosons subject to Rabi coupling and magnetic detuning, where the liquid-gas transition can be conveniently tuned and their coexistence can be characterized by a discontinuous density profile in a harmonic trap. The spin twist scheme for LGTC can be generalized to a wide class of quantum systems with competing single-particle and interaction orders.

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• Bose gases
• Mixtures of atomic and/or molecular quantum gases
• Quantum fluids & solids
• Spinor Bose-Einstein condensates