arXiv subjects
Publications and source records attributed to Alexander S. Shumovsky.
We resolve an old problem about the existence of hidden parameters in a three-dimensional quantum system by constructing an appropriate Bell's type inequality. This reveals a nonclassical nature of most spin-$1$ states. We shortly discuss some physical implications and an underlying cause of this nonclassical behavior, as well as a perspective of its experimental verification.
Using a single spin-1 object as an example, we discuss a recent approach to quantum entanglement. The key idea of the approach consists in presetting of basic observables in the very definition of quantum system. Specification of basic observables defines the dynamic symmetry of the system. Entangled states of the system are then interpreted as states with maximal amount of uncertainty of all basic observables. The approach gives purely physical picture of entanglement. In particular, it separates principle physical properties of entanglement from inessential. Within the model example under consideration, we show relativity of entanglement with respect to dynamic symmetry and argue existence of single-particle entanglement. A number of physical examples are considered.
We show that entanglement of pure multi-party states can be quantified by means of quantum uncertainties of certain basic observables through the use of measure that has been initially proposed in [10] for bipartite systems.
Amount of entanglement carried by a quantum bipartite state is usually evaluated in terms of concurrence (see Ref. 1). We give a physical interpretation of concurrence that reveals a way of its direct measurement and discuss possible generalizations.
We discuss maximum entangled states of quantum systems in terms of quantum fluctuations of all essential measurements responsible for manifestation of entanglement. Namely, we consider maximum entanglement as a property of states, for which quantum fluctuations come to their extreme.
We show that a system of 2n identical two-level atoms interacting with n cavity photons manifests entanglement and that the set of entangled states coincides with the so-called SU(2) phase states. In particular, violation of classical realism in terms of the GHZ and GHSH conditions is proved. We discuss a new property of entanglement expressed in terms of local measurements. We also show that generation of entangled states in the atom-photon systems under consideration strongly depends on the choice of initial conditions and that the parasitic influence of cavity detuning can be compensated through the use of Kerr medium.
We show that the maximum entanglement in a composite system corresponds to the maximum uncertainty and maximum correlation of local measurements.
A general form of the polarization matrix valid for any type of electromagnetic radiation (plane waves, multipole radiation etc.) is defined in terms of a certain bilinear form in the field-strength tensor. The quantum counterpart is determined as an operator matrix with normal-ordered elements with respect to the creation and annihilation operators. The zero-point oscillations (ZPO) of polarization are defined via difference between the anti-normal and normal ordered operator polarization matrices. It is shown that ZPO of the multipole field are stronger than those described by the model of plane waves and are concentrated in a certain neighborhood of a local source.
We discuss the spatial properties of quantum radiation emitted by a multipole transition in a single atom. The qualitative difference between the representations of plane and spherical waves of photons is examined. In particular, the spatial inhomogeneity of the zero-point oscillations of multipole field is shown. We show that the vacuum noise of polarization is concentrated in a certain vicinity of atoms where it strongly exceeds the level predicted by the representation of the plane waves. A new general polarization matrix is proposed. It is shown that the polarization and its vacuum noise strongly depend on the distance from the source.
Description of detection and emission in terms of the photon localization is discussed. It is shown that the standard representation of plane waves of photons should be revised to take into consideration the boundary conditions caused by the presence of quantum emitters and detectors. In turn, the change of the boundary conditions causes spatially inhomogeneous structure of the electromagnetic vacuum which leads to the increase of the vacuum noise over the level predicted in the frame of the model of plane photons.
New effective operators, describing the photons with given polarization at given position with respect to a source are proposed. These operators can be used to construct the near and intermediate zones quantum optics. It is shown that the use of the conventional plane photons can lead to a wrong results for quantum fluctuations of polarization even in the far zone.
A general fundamental relation connecting the correlation of Stokes and anti-Stokes modes to the quantum statistical behavior of vibration and pump modes in Raman-active materials is derived. We show that under certain conditions this relation can be used to determine the equilibrium number variance of phonons.Time and temperature ranges for which such conditions can be satisfied are studied and found to be available in todays' experimental standards. Furthermore, we examine the results in the presence of multi-mode pump as well as for the coupling of pump to the many vibration modes and discuss their validity in these cases.