Anatoly Khitrin

Anatoly Khitrin could play guitar, fix home appliances, or cure snoring with a self-built device. But his main passion was of course physics. His easy ways with physics reminded one of a skillful pianist in full control of the keyboard; he was equally at home with mechanics, materials, electricity, quantum theory, or almost any other physical discipline. After talking for 20 minutes with a biologist or a climate scientist about their work, he could often see deeper aspects of their particular problem than his professional interlocutors. This unique ability to penetrate diverse subjects came from his extraordinary grasp of the main physical principles; he went straight to the core of the problem where others got lost in a thicket of details.

When asked about a certain arcane theory of optical microscopy, he immediately realized that image formation in a transmission microscope can often be understood from the geometrical standpoint. The role of a refractive object is to alter the intensity distribution at the focal plane, and that is what we see. The result was a formula that was almost equivalent to the one known from the diffraction theory but much easier to understand intuitively or to solve computationally.¹ Simple as it sounds, no one had ever described microscopic images in the same terms before.

Another example comes from membrane biophysics. An extensive theory exists on how charged molecules interact with biological membranes. But after pondering it for a few hours, Anatoly noticed something that had eluded everyone else: that cells have a closed shape, and that means that no electric field can exist in their interior. But, on the other hand, it is known that positively charged molecules do get attracted to the negative membrane: Does this fact not disprove the theory? After a few more hours, a new model of electrostatic interactions was born, astonishing in its novelty and simplicity. In particular, it follows from his model that like charges in a conducting liquid may experience attraction across a dielectric membrane. In fact, Anatoly’s arguments were so simple that they could be easily explained on two square inches of paper, and yet the result was entirely new.²

In his main area of NMR spectroscopy, Anatoly’s contributions were deep and wide-reaching, as well as practical. His spin decoupling technique³ is now used by many researchers to study molecules and liquid crystals. He discovered the phenomenon of long-lived signal excitations,⁴ which can become a game-changing imaging technique for MRI of bone or other rigid tissues. He developed an original approach for obtaining proton NMR spectra of water and ethanol in gasoline.⁵ Not lacking a sense of humor, he went on to apply it to Smirnoff vodka.

A few years ago, he turned to the fundamental question of reversibility in dynamical physical systems. How much can we know about the past and how well can we predict the future? His analysis of small perturbations in a nuclear spin system led him to a paradoxical conclusion that quantum dynamical systems can be more reversible than their classical counterparts.⁶ Anatoly argued forcefully for the potential of NMR spectroscopy to bring a deeper understanding of fundamental problems in the dynamical evolution of many-body systems. This work, as well as some of his other pioneering efforts in using spin systems to explore quantum information processing and quantum computing, can be hoped to stimulate further progress in broad regions of physics beyond NMR spectroscopy.

Anatoly was modest and easygoing, unconcerned with grants, rankings, and honors. It seemed that his idea of a perfect day was to stay home undisturbed, think, work and read. He always looked relaxed and friendly. On occasion, he would catch mistakes made by seminar speakers and give them a hard time, but overall, he projected a kind of upbeat and gentle equanimity and understanding—something of a Democritus, the “laughing philosopher.” When one professor at Kent State University, a young and successful scientist, learned of Anatoly’s death, he wrote to one of the authors of this paper: “Anatoly helped me become a better scientist and a better person.” It is a fitting tribute to a man who will be missed by all his friends and colleagues.

References

1. A. K. Khitrin et al., Microscopy and Microanalysis 23, 1116 (2017).
2. A. K. Khitrin et al., Chem. Phys. Lipids 184, 76 (2014).
3. B. M. Fung et al., J. Magn. Reson. 142, 97 (2000).
4. B. Zhang et al., J. Magn. Reson. 231, 1 (2013).
5. A. K. Khitrin, J. Magn. Reson. 213, 22 (2011).
6. A. K. Khitrin, Phys. Rev. E 92, 052903 (2015).