A quantum gas of ultracold polar molecules with long-range and anisotropic interactions enables exploration of many-body physics and quantum information processing. The study reports the creation of a dense gas of 40K87Rb polar molecules, achieving a peak density of 10¹² cm⁻³ and a translational temperature of 350 nK. The molecules have permanent electric dipole moments measured as 0.052(2) D for the triplet state and 0.566(17) D for the singlet state. The research demonstrates efficient coherent transfer of ultracold atoms into the rovibrational ground state of both triplet and singlet electronic ground molecular potentials using STIRAP. This process creates a high phase-space-density gas of polar molecules, enabling the study of dipole-dipole interactions. The molecules are created in an optical dipole trap and their expansion energy is kb·350 nK. The study also reports the creation of absolute ground-state polar molecules, with a measured electric dipole moment of 0.566(17) D for the singlet state, which is significantly larger than that of the triplet state. The research highlights the potential of ultracold polar molecules for exploring quantum phase transitions, quantum gas dynamics, and quantum simulations of condensed matter systems. The study demonstrates the creation of a high phase-space-density gas of polar molecules, which is essential for studying interactions in quantum systems. The results show that the molecules can be polarized by modest electric fields, facilitating the exploration of interaction effects. The study also demonstrates the creation of absolute ground-state molecules using a single-step STIRAP process, achieving a roundtrip transfer efficiency of 69% and a one-way transfer efficiency of 83%. The molecules have a longer lifetime than triplet rovibrational ground-state molecules, making them suitable for future studies of dipolar Fermi and Bose-Einstein condensates. The research provides a foundation for the development of quantum technologies based on ultracold polar molecules.A quantum gas of ultracold polar molecules with long-range and anisotropic interactions enables exploration of many-body physics and quantum information processing. The study reports the creation of a dense gas of 40K87Rb polar molecules, achieving a peak density of 10¹² cm⁻³ and a translational temperature of 350 nK. The molecules have permanent electric dipole moments measured as 0.052(2) D for the triplet state and 0.566(17) D for the singlet state. The research demonstrates efficient coherent transfer of ultracold atoms into the rovibrational ground state of both triplet and singlet electronic ground molecular potentials using STIRAP. This process creates a high phase-space-density gas of polar molecules, enabling the study of dipole-dipole interactions. The molecules are created in an optical dipole trap and their expansion energy is kb·350 nK. The study also reports the creation of absolute ground-state polar molecules, with a measured electric dipole moment of 0.566(17) D for the singlet state, which is significantly larger than that of the triplet state. The research highlights the potential of ultracold polar molecules for exploring quantum phase transitions, quantum gas dynamics, and quantum simulations of condensed matter systems. The study demonstrates the creation of a high phase-space-density gas of polar molecules, which is essential for studying interactions in quantum systems. The results show that the molecules can be polarized by modest electric fields, facilitating the exploration of interaction effects. The study also demonstrates the creation of absolute ground-state molecules using a single-step STIRAP process, achieving a roundtrip transfer efficiency of 69% and a one-way transfer efficiency of 83%. The molecules have a longer lifetime than triplet rovibrational ground-state molecules, making them suitable for future studies of dipolar Fermi and Bose-Einstein condensates. The research provides a foundation for the development of quantum technologies based on ultracold polar molecules.