The memory effect in the form of hysteresis has been detected in the measured dependence of the intensity of the photon echo in YLiF 4 and LuLiF 4 samples with Er 3+ impurity ions on the orientation, strength, and variation direction of the magnetic field. The prehistory of the location of a sample in the magnetic field with a certain direction and strength is written and stored for no less than 6 h at a temperature of 2 K. The effect crucially depends on the orientation of the optical axis of the sample with respect to the external magnetic field.

The collapse and revival of Hahn electron spin echo signals excited on electron–nuclear spin levels of an impurity 173Yb3+ ion in yttrium orthosilicate Y2SiO5 have been detected. A model of the phenomenon has been proposed on the basis of the combination of the conventional mechanism of the formation of two-pulse Hahn echo and the mechanism of the formation of echo signals on spin frequency combs that are hidden in the inhomogeneous width of resonance lines and are due to the hyperfine interaction of the electron spin of the Yb3+ ion with surrounding nuclear spins of 89Y.

When describing the dynamics of quantum systems interacting with a coherent external electromagnetic field, the instant at which the exciting (measuring) field begins to act is traditionally taken as zero time in the laboratory frame. Using the concept of coherence sudden death in an observed quantum system, we introduce the definition of local, completely incoherent subensembles of the quantum system in which it is found with a certain probability at each instant of time in the process of a continuous observation (measurement). For such subensembles an arbitrary instant of time in the laboratory frame is the initial time of the interaction with the external (measuring) field. As a result, the dynamics of an open quantum system is represented by a superposition of the dynamics of local subsystems with a continuous distribution of the times at which the interaction with the external field begins. We have derived an expression for the dynamical “multitime” contribution to the stationary solution of the Bloch equations, which clearly demonstrates the meaning of time relativity in the dynamics of two-level quantum systems in the semiclassical approximation. This dynamical multitime contribution is shown to explain the emergence of quantum beats at zero frequency (the Hanle effect, the level crossing) in EPR.

A signal related to the spin level crossing in a zero magnetic field—the Hanle effect—has been registered for the first time in the EPR spectrum. It has been shown that, in the general case, the shape of the signal is determined by two qualitatively different mechanisms: (i) the interference of unsteady-state contributions to the dynamics of atomic coherences (electric or magnetic quantum transition moments with certain phases) with close frequencies (“beats at a zero frequency”) and (ii) the summation of resonant signals determined by the steady-state dynamics of the same atomic coherences. The relaxation time of spin coherences has been determined for the EPR transition of Tm3+ ions in synthetic forsterite.

Continuous-wave electron paramagnetic resonance spectra of impurity holmium ions in synthetic forsterite have been studied on an ELEXSYS E580 spectrometer equipped with a cylindrical dielectric resonator ER4118MD5-W1 of the Flexline series. Resonance lines of the anomalous shape demonstrating the absorption contour instead of its derivative were observed at the conventional operation mode with the magnetic field modulation. The conditions of the appearance of anomalous signals and their characteristics have been studied. The anomalous lines shape effect was explained by the simultaneous excitation of magnetic dipole and electric quadrupole transitions between electron–nuclear spin sublevels of the holmium ions.

The anomalous dependence of the electron paramagnetic resonance (EPR) line shape on the microwave power in the resonator has been found when studying the continuous-wave EPR spectra of impurity holmium ions in synthetic forsterite on an ELEXSYS E 580 EPR spectrometer. The power-threshold transition from the conventional lines being the derivatives of the spectral line contours to the spectral line contours themselves has been observed as the power increased. The properties of the anomalous EPR lines are qualitatively explained assuming that the resonance electric quadrupole transitions take place between the electron spin levels.

The correlated dynamics of a three-level atom resonantly coupled to an electromagnetic cavity field is calculated (Λ, V, and L models). A diagrammatic representation of quantum dynamics is proposed for these models. As an example, Λ-atom dynamics is examined to demonstrate how the use of conventional von Neumann’s reduction leads to internal decoherence (disentanglement-induced decoherence) and to the absence of atomic coherence under multiphoton excitation. The predicted absence of atomic coherence is inconsistent with characteristics of an experimentally observed atom-photon entangled state. It is shown that the correlated reduction of a composite quantum system proposed in [18] qualitatively predicts the occurrence and evolution of atomic coherence under multiphoton excitation if a seed coherence is introduced into any subsystem (the atom or a cavity mode).

Pedagogical introduction into the problem of the mathematical description of the quantum correlation (entanglement) of composite quantum systems is represented. The notion is substantiated about the fact that the conventional algorithm of the reduction of von Neumann in the description of the dynamics of the observed subsyatem is not universal and corresponds only to the case of maximum macroscopicity of the unobservable subsystem. Is clearly shown the sense of the algorithm of the correlated reduction proposed, which minimally changes the entropy of composite system.

We show that the von Neumann’s algorithm of reduction (i.e. the algorithm of calculating the density matrix of the observable subsystem from the density matrix of the closed quantum system) corresponds to the special approximation at which the unobservable subsystem is supposed to be in the steady state of minimum information (infinite temperature) . We formulate the generalized algorithm of reduction that includes as limiting cases the von Neumann’s reduction and the selfcongruent correlated reduction most corresponding to the quantum nondemolition measurement. We demonstrate the correlation in dynamics of subsystems with exactly soluble models of quantum optics: 1) about the dynamics of a pair of interacting two-level atoms, and 2) about the dynamics of a two-level atom interacting with a single-mode resonant field.

It is shown that the standard reduction procedure (i.e., the calculation of the density matrix of the observable subsystem from the density matrix of a closed quantum system) bringing about decoherence corresponds to the limiting approximation, where the unobservable subsystem is assumed to be in the stationary state with minimum information (infinite temperature). An approximate set of interrelation (correlation) equations for the density matrices of the subsystems is derived. It is shown that the correlation of atom and field can be manifested as the inversion beats of a two-level atom in the known experimental scheme of resonator QED. Experimental observation of such beats would indicate that the observable subsystem (atom) generally conserves information about quantum coherence of the unobservable subsystem (field).

The results on the magnetic field dependence of the intensity of a microwave echo in silicate glasses containing paramagnetic impurities are used to construct a model of the formation of an echo as a super-position of an acoustic electron spin echo of the system of paramagnetic impurities and a polarization echo of the ensemble of quartz microcrystals present in the glass. Representing microcrystals in the glass as an ensemble of acoustic oscillators makes it possible to explain the anomalous low-temperature specific heat of glasses without invoking the model of localized two-level tunneling centers.

Absorption measurements are reported for ruby irradiated with Ar+ laser light. The charge state of chromium ions is analyzed, and the parameters of photoinduced electrical domain structure are evaluated.

The three known models of quantum optics concerned the resonant interaction of three-level atom with two modes of field (Lambda-, V- and Xi-atom) was demonstrated to have the one general solution. The diagonalization method of block matrices was used to calculate the evolution operator of the atom-field interaction Hamiltonian. The method is outlined in detail by the example of the Lambda-atom model.

The dependence of the rate of formation and erasure of photoinduced electrical domain structure in ruby on the spectral composition of nonlaser illumination is studied. Near-ultraviolet irradiation is found to cause rapid erasure of the domain structure. The photocurrent density and photoconductivity are determined as functions of the electric field strength of the domains during irradiation with different spectral compositions at 77 K and 300 K assuming a “capacitor” model for the domains. The dark conductivity of ruby is estimated.

Using the solution of the Jaynes-Cummings problem, we define operators inverse of the bosonic operators of creation and annihilation. We demonstrate the properties of these operators by calculating commutators, products, and the results of action of these operators on certain states of the field.