Surprising quantum effects

Yasunori Fujii, Kei‐ichi Maeda

Marlan O. Scully, Chris J. Bednar, Yuri V. Rostovtsev +1 more

The study of an ensemble of phase–coherent atoms has recently lead to interesting theoretical innovations and experimental demonstrations of counter–intuitive effects such as electromagnetically induced transparency (EIT), lasing without inversion (LWI), enhancement of index of refraction and ultra–large nonlinear susceptibility. In the present notes, we report a couple of new effects along these lines. In fact, it would be fair to call them surprises even in the repertoire of ‘counter–intuitive effects’, i.e. ‘counter–counter–intuitive effects’. Specifically, we will show that the LWI concept, which is based on quantum coherence, has a surprising counterpart in the classical physics of free electron laser operation. In other current work, we find that it is possible to ‘lock’ atoms in an excited state via atomic coherence. It is, by now, not surprising that such a phase–coherent ensemble can show holes or dark lines in the emission spectrum. It is surprising that we can lock atoms in an excited (normally decaying) state via atomic coherence and interference. Such a phase–coherent collection of atoms, i.e. ‘phaseonium’, is indeed a novel new state of matter.

Ksenia Komarova, F. Remacle, Raphael David Levine

Progress toward quantum technologies continues to provide essential new insights into the microscopic dynamics of systems in phase space. This highlights coherence effects whether these are due to ultrafast lasers whose energy width spans several states all the way to the output of quantum computing. Surprisal analysis has provided seminal insights into the probability distributions of quantum systems from elementary particle and also nuclear physics through molecular reaction dynamics to system biology. It is therefore necessary to extend surprisal analysis to the full quantum regime where it characterizes not only the probabilities of states but also their coherence. In principle, this can be done by the maximal entropy formalism, but in the full quantum regime, its application is far from trivial [S. Dagan and Y. Dothan, Phys. Rev. D 26, 248 (1982)] because an exponential function of non-commuting operators is not easily accommodated. Starting from an exact dynamical approach, we develop a description of the dynamics where the quantum mechanical surprisal, a linear combination of operators, plays a central role. We provide an explicit route to the Lagrange multipliers of the system and identify those operators that act as the dominant constraints.

Tahir Iqbal, Almas Bashir, Aqsa Tehseen

Derrick S. F. Crothers, R. J. S. Lee

In `On the quantum mechanics of particles with classically assigned trajectories', Barton and Calogeracos (1996 Proc. R. Soc. A 452 1167) find that the wavefunction surprisingly acquires an overall phase factor of the form exp(+i∫ 0 t E ( t ') d t '), surprising in that the conjugate was expected, with E the relative kinetic energy. It is shown that, with the correct interpretation in terms of electron translation phase factors, there is no surprise and the effect is well known experimentally and theoretically in charge transfer and ionization in ion-atom collisions.