Martinis are forever

Marcus Chown

Andrew N. Cleland, S. M. Girvin

The Royal Swedish Academy of Sciences awarded the 2025 Nobel Prize in Physics jointly to John Clarke, Michel H. Devoret, and John M. Martinis for their foundational discovery of macroscopic quantum mechanical tunneling and energy quantization in electrical circuits. The work that was honored was conducted primarily in the mid-1980s in John Clarke’s laboratory at the University of California—Berkeley, as described in two articles in Physical Review Letters [M. H. Devoret, J. M. Martinis, J. Clarke, Phys. Rev. Lett. 55 , 1908–1911 (1985); J. M. Martinis, M. H. Devoret, J. Clarke, Phys. Rev. Lett. 55 , 1543–1546 (1985)]. This work effectively bridged the gap between the microscopic world of atoms and the macroscopic world of human-scale engineering.

Xiao Liang, YaDong Wu, Hui Zhai

Hamid Arian Zad, Jozef Strečka

The spin-1/2 Ising-Heisenberg model on martini and martini-diced lattice is exactly solved using a star-triangle transformation, which affords an exact mapping correspondence to an effective spin-1/2 Ising model on a triangular lattice. The ground-state phase diagram of both investigated quantum spin models display two spontaneously ordered ferromagnetic phases and one macroscopically degenerate disordered phase. In contrast to a classical ferromagnetic phase where the spontaneous magnetization of the Ising as well as Heisenberg spins acquire fully saturated values the spontaneous magnetization of the Heisenberg spins is subject to a quantum reduction to one-third of its saturated value within a quantum ferromagnetic phase. The spontaneous magnetization and logarithmic divergence of the specific heat as the most essential features of both ferromagnetic phases disappear whenever the investigated quantum spin model is driven to the highly degenerate disordered phase. The disordered phase with nonzero residual entropy originates either from a geometric spin frustration caused by antiferromagnetic interactions or more strikingly it may also alternatively arise from a competition of the ferromagnetic Ising and Heisenberg interactions of easy-axis and easy-plane type, respectively. All three available ground states coexist together at a single triple point, around which anomalous magnetic and thermodynamic behavior can be detected.

Hamid Arian Zad, Jozef Strečka

The spin-1/2 Ising-Heisenberg model on martini and martini-diced lattices is exactly solved using a star-triangle transformation, which affords an exact mapping correspondence to an effective spin-1/2 Ising model on a triangular lattice. The ground-state phase diagram of both investigated quantum spin models display two spontaneously ordered ferromagnetic phases and one macroscopically degenerate disordered phase. In contrast to a classical ferromagnetic phase where the spontaneous magnetization of the Ising as well as Heisenberg spins acquire fully saturated values, the spontaneous magnetization of the Heisenberg spins is subject to a quantum reduction to one-third of its saturated value within a quantum ferromagnetic phase. The spontaneous magnetization and logarithmic divergence of the specific heat as the most essential features of both ferromagnetic phases disappear whenever the investigated quantum spin model is driven to the highly degenerate disordered phase. The disordered phase with nonzero residual entropy originates either from a geometric spin frustration caused by antiferromagnetic interactions or more strikingly it may also alternatively arise from a competition of the ferromagnetic Ising and Heisenberg interactions of easy-axis and easy-plane type, respectively. All three available ground states coexist together at a single triple point, around which anomalous magnetic and thermodynamic behavior can be detected.