We show that molecules and nuclei with well-expressed rotational degrees of freedom can be excited by means of a multistep process, initiated by a short and sufficiently strong electromagnetic pulse, into a coherent superposition of rotational states. Properties of a molecule or a nucleus in such a nonstationary state change (quasi-) periodically in time, due to the fact that the energies of the rotational states satisfy (approximately) the rule \ensuremath{\omega}J(J+1). Accordingly, their interaction with an electromagnetic field or with other particles changes (quasi-) periodically in time. A gas of molecules in a coherent state exhibits a (quasi-) periodic change of the refractive index, an effect which has been observed for the case of ${\mathrm{CS}}_{2}$ gas at 325 K. The nuclear case does not lead to direct experimental detection, because of its short coherence period.We show that molecules and nuclei with well-expressed rotational degrees of freedom can be excited by means of a multistep process, initiated by a short and sufficiently strong electromagnetic pulse, into a coherent superposition of rotational states. Properties of a molecule or a nucleus in such a nonstationary state change (quasi-) periodically in time, due to the fact that the energies of the rotational states satisfy (approximately) the rule \ensuremath{\omega}J(J+1). Accordingly, their interaction with an electromagnetic field or with other particles changes (quasi-) periodically in time. A gas of molecules in a coherent state exhibits a (quasi-) periodic change of the refractive index, an effect which has been observed for the case of ${\mathrm{CS}}_{2}$ gas at 325 K. The nuclear case does not lead to direct experimental detection, because of its short coherence period.

Physical Review AMay 1, 198718 citations

Time evolution of coherent states

Prakash Chand

Il Nuovo cimento della Società italiana di fisica. B/Il Nuovo cimento BMar 1, 19792 citations

Role of the counter-rotating terms in the creation of entanglement between two atoms

Z. Ficek, Jun Jing, Zhiguo Lü

The problem of the creation of entanglement exclusively from the presence of the counter-rotating terms in the interaction Hamiltonian between two atoms and a single-mode cavity field is studied. The time evolution of the concurrence between the atoms is discussed for two different initial separable states and arbitrary strengths of the coupling constants of the atoms to the cavity mode. We show that a transient entanglement can be created between the atoms only if the counter-rotating terms are taken into account in the interaction Hamiltonian. The source of the entanglement is identified, and the entanglement features are explained in terms of the properties of the reduced density operator of the atoms. In particular, we find that the main source of the entanglement is in the two-photon coherence induced by the counter-rotating terms that cause two-photon transitions through virtual states.The problem of the creation of entanglement exclusively from the presence of the counter-rotating terms in the interaction Hamiltonian between two atoms and a single-mode cavity field is studied. The time evolution of the concurrence between the atoms is discussed for two different initial separable states and arbitrary strengths of the coupling constants of the atoms to the cavity mode. We show that a transient entanglement can be created between the atoms only if the counter-rotating terms are taken into account in the interaction Hamiltonian. The source of the entanglement is identified, and the entanglement features are explained in terms of the properties of the reduced density operator of the atoms. In particular, we find that the main source of the entanglement is in the two-photon coherence induced by the counter-rotating terms that cause two-photon transitions through virtual states.

Physica ScriptaSep 1, 201013 citations

Coherent rotational states in nuclear and molecular systems

Norma Mankoč Borštnik

Jan 1, 19850 citations

Semiclassical description of quantum rotator in terms ofSU(2) coherent states

Dmitri M Gitman, D. A. Petrusevich, A. L. Shelepin

We introduce coordinates of the rigid body (rotator) using mutual positions between body-fixed and space-fixed reference frames. Wave functions that depend on such coordinates can be treated as scalar functions of the group SU(2). Irreducible representations of the group SU(2) × SU(2) in the space of such functions describe their possible transformations under independent rotations of the both reference frames. We construct sets of the corresponding group SU(2) × SU(2) Perelomov coherent states (CS) with a fixed angular momentum j of the rotator as special orbits of the latter group. Minimization of different uncertainty relations is discussed. The classical limit corresponds to the limit j → ∞. Considering Hamiltonians of rotators with different characteristics, we study the time evolution of the constructed CS. In some cases, the CS time evolution is completely or partially reduced to their parameter time evolution. If these parameters are chosen as Euler angles, then they obey the Euler equations in the classical limit. Quantum corrections to the motion of the quantum rotator can be found from exact equations on the CS parameters.We introduce coordinates of the rigid body (rotator) using mutual positions between body-fixed and space-fixed reference frames. Wave functions that depend on such coordinates can be treated as scalar functions of the group SU(2). Irreducible representations of the group SU(2) × SU(2) in the space of such functions describe their possible transformations under independent rotations of the both reference frames. We construct sets of the corresponding group SU(2) × SU(2) Perelomov coherent states (CS) with a fixed angular momentum j of the rotator as special orbits of the latter group. Minimization of different uncertainty relations is discussed. The classical limit corresponds to the limit j → ∞. Considering Hamiltonians of rotators with different characteristics, we study the time evolution of the constructed CS. In some cases, the CS time evolution is completely or partially reduced to their parameter time evolution. If these parameters are chosen as Euler angles, then they obey the Euler equations in the classical limit. Quantum corrections to the motion of the quantum rotator can be found from exact equations on the CS parameters.

Physica ScriptaSep 17, 20131 citation

{\mathrm{CS}}_{2}

gas at 325 K. The nuclear case does not lead to direct experimental detection, because of its short coherence period.