Quantum physicists have demonstrated a striking counterintuitive effect: when two rotational motions combine in a special crystal, they can produce a motion spinning in the exact opposite direction, effectively making “1 + 1 = -1.”Using intense terahertz laser pulses, researchers excited collective atomic vibrations (phonons) in a bismuth selenide crystal, driving them into circular orbits. High-speed stroboscopic measurements then revealed that the transfer of rotational (angular) momentum between different vibration modes caused the overall spin direction to suddenly reverse.This surprising reversal is made possible by the crystal’s unique threefold rotational symmetry, which allows certain opposing rotational states to become physically equivalent. As a result, the combined motions “fold backward” in a quantum flipping mechanism.The breakthrough provides the first direct experimental evidence of how angular momentum is conserved and redistributed through nonlinear interactions in a crystal lattice. It also establishes a new research field called helical nonlinear phononics.[Minakova, O., Paiva, C., Frenzel, M., Spencer, M. S., Urban, J. M., Ringkamp, C., Wolf, M., Mussler, G., Juraschek, D. M., & Maehrlein, S. F. (2026). Observation of angular momentum transfer among crystal lattice modes. Nature Physics. DOI: 10.1038/s41567-026-03274-8]Science and facts💡
![Quantum physicists have demonstrated a striking counterintuitive effect: when two rotational motions combine in a special crystal, they can produce a motion spinning in the exact opposite direction, effectively making “1 + 1 = -1.”Using intense terahertz laser pulses, researchers excited collective atomic vibrations (phonons) in a bismuth selenide crystal, driving them into circular orbits. High-speed stroboscopic measurements then revealed that the transfer of rotational (angular) momentum between different vibration modes caused the overall spin direction to suddenly reverse.This surprising reversal is made possible by the crystal’s unique threefold rotational symmetry, which allows certain opposing rotational states to become physically equivalent. As a result, the combined motions “fold backward” in a quantum flipping mechanism.The breakthrough provides the first direct experimental evidence of how angular momentum is conserved and redistributed through nonlinear interactions in a crystal lattice. It also establishes a new research field called helical nonlinear phononics.[Minakova, O., Paiva, C., Frenzel, M., Spencer, M. S., Urban, J. M., Ringkamp, C., Wolf, M., Mussler, G., Juraschek, D. M., & Maehrlein, S. F. (2026). Observation of angular momentum transfer among crystal lattice modes. Nature Physics. DOI: 10.1038/s41567-026-03274-8]Science and facts💡](https://cdn4.telesco.pe/file/vRRBI5PBORW0rUkBhg5P_kzV5qjbD4DeI7-4PMI5MXKOtvMSsU_RNweq0AYjt8QtjJ-qhdCRG846YbdV6fRSvus0EwfF77ItbTPq5eOSsJuXJ3PcJNrcrIWK6pS2ewTgf-AvILqmyWBA9eBrFsvJkXsuUicut655zcCFqRTEHAIiS_JdFf-NVDJ7gDX-0O3ObZC88wufVAjqpFZvF-U29BguQo52EcLYAcmCfl64gIOwdWgWa67Pt7h4gw4pqIjpHPS2HPcehoQ2I5QX2_CqzLsZ0eK9gXqszwUqDHoCC79AlW9laz0WJ3pBry0t6nwfgZr_aKRasfpAmAu23WmndQ.jpg)
Quantum physicists have demonstrated a striking counterintuitive effect: when two rotational motions combine in a special crystal, they can produce a motion spinning in the exact opposite direction, effectively making “1 + 1 = -1.”Using intense terahertz laser pulses, researchers excited collective atomic vibrations (phonons) in a bismuth selenide crystal, driving them into circular orbits. High-speed stroboscopic measurements then revealed that the transfer of rotational (angular) momentum between different vibration modes caused the overall spin direction to suddenly reverse.This surprising reversal is made possible by the crystal’s unique threefold rotational symmetry, which allows certain opposing rotational states to become physically equivalent. As a result, the combined motions “fold backward” in a quantum flipping mechanism.The breakthrough provides the first direct experimental evidence of how angular momentum is conserved and redistributed through nonlinear interactions in a crystal lattice. It also establishes a new research field called helical nonlinear phononics.[Minakova, O., Paiva, C., Frenzel, M., Spencer, M. S., Urban, J. M., Ringkamp, C., Wolf, M., Mussler, G., Juraschek, D. M., & Maehrlein, S. F. (2026). Observation of angular momentum transfer among crystal lattice modes. Nature Physics. DOI: 10.1038/s41567-026-03274-8]Science and facts💡
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