Vishal Varma (Indian Institute of Science Education and Research (IISER) Pune, India)
Abstract: In NMR spectroscopy, the longitudinal relaxation that destroys both classical and quantum information by restoring the spin populations to thermal equilibrium has traditionally hindered our ability to harness the full potential of spin dynamics. However, the emergence of long-lived states (LLS) has challenged this notion. With lifetimes significantly exceeding the spin-lattice relaxation time constant T1, LLS has revolutionized the field, enabling advanced medical imaging, chemical analysis, and quantum information processing applications.
While LLS has predominantly been observed in isotropic phases, its presence in anisotropic phases has remained an intriguing question. I will show that LLS can be prepared in a two-spin system oriented in a liquid crystal solvent and, even more strikingly, demonstrate that it can survive the phase transition from the oriented phase to the isotropic phase when subjected to heating. This resilience highlights the untapped potential of LLS in various applications.
Reference(s):
V. Varma and T. S. Mahesh, “Long-Lived Singlet State in an Oriented Phase and its Survival across the Phase Transition Into an Isotropic Phase,” Phys. Rev. Applied 20, 034030 (2023).
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Why do you use M2S in the partially oriented phase and smth like the Sarkar sequence in the isotropic phase? How long does it take for the phase transition to occur, and how does this time compare to the lifetime(s) of LLS in the oriented phase and in the isotropic phases?
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Hi Kirill Sheberstov. The spins are strongly coupled in the partially oriented phase; therefore, we use the M2S sequence. We use the Sarkar sequence in the isotropic phase due to weak coupling between the two spins.
The phase transition takes less than 30 seconds. We turn on the probe heater 10 seconds before the M2S, because it takes a few seconds before a significant temperature rise is observed. The rest of the time is spent during storage when the WALTZ-16 sequence is applied.
Near the transition temperature, the LLS lifetime is 4.6 seconds (in oriented phase) and above 8 seconds (in isotropic phase). So we give minimum 16 seconds of storage time before acquiring the signal with the Sarkar sequence in isotropic phase. This delay is above 5*T_lls for both the oriented and isotropic phases.
Thanks for your interest.
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Hello, this presentation appears to be from the viewpoint that survival of the long-lived singlet (LLS) state would be unexpected upon a phase transition. Could you clarify why undergoing a phase transition might eliminate all the coherent signal associated with the LLS state? Did your understanding change as a result of making these experimental measurements? Are you able to comment on whether there is a ‘scaling’ in the amount of LLS coherence when undergoing the phase transition (for example, is some portion irreversibly lost, or does it appear to be quantitatively ‘all there’ after accounting for otherwise ‘normal’ relaxation processes that would occur during the time associated with the phase transition)?
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Hello. Thank you for your questions.
As the phase transition happens, the structure of the Hamiltonian changes. The residual dipolar coupling is decreasing with the temperature, and we were unsure whether the LLS would survive this change! We found that the LLS survives this, and we verified that the signal observed in the isotropic phase originates from the LLS coherence prepared in the oriented phase.
Regarding the question of scaling in the amount of LLS coherence, I think some part is irreversibly lost because the heating of the sample is non-uniform. Some parts of the sample might not have been entirely converted to the liquid phase, making it a mixed phase. Moreover, since the detection sequence in the isotropic phase is designed to detect the LLS coherence in the isotropic phase, it might also be that some LLS coherence was not observed.
I appreciate your questions. Please let me know if my answer is unclear or if I have misunderstood the question. I would be happy to discuss. Thanks again.
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Thank you for your responses.
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