arXiv subjects

A. A. Semenov

Publications and source records attributed to A. A. Semenov.

51 records · Page 3Linked to original sources

arXiv2008

Dynamics of Cryogenic Jets: Non-Rayleigh Breakup and Onset of Nonaxisymmetric Motions

We report development of generators for periodic, satellite-free fluxes of mono-disperse drops with diameters down to 10 mikrometers from cryogenic liquids like H_2, N_2, Ar and Xe (and, as reference fluid, water). While the breakup of water jets can well be described by Rayleigh's linear theory, we find jet regimes for H_2 and N_2 which reveal deviations from this behavior. Thus, Rayleigh's theory is inappropriate for thin jets that exchange energy and/or mass with the surrounding medium. Moreover, at high evaporation rates, axial symmetry of the dynamics is lost. When the drops pass into vacuum, frozen pellets form due to surface evaporation. The narrow width of the pellet flux paves the way towards various industrial and scientific applications.

physics.flu-dyn↗

arXiv2007

Determination of quantum-noise parameters of realistic cavities

A procedure is developed which allows one to measure all the parameters occurring in a complete model [A.A. Semenov et al., Phys. Rev. A 74, 033803 (2006); quant-ph/0603043] of realistic leaky cavities with unwanted noise. The method is based on the reflection of properly chosen test pulses by the cavity.

quant-ph↗

arXiv2006

Leaky cavities with unwanted noise

A phenomenological approach is developed that allows one to completely describe the effects of unwanted noise, such as the noise associated with absorption and scattering, in high-Q cavities. This noise is modeled by a block of beam splitters and an additional input-output port. The replacement schemes enable us to formulate appropriate quantum Langevin equations and input-output relations. It is demonstrated that unwanted noise renders it possible to combine a cavity input mode and the intracavity mode in a nonmonochromatic output mode. Possible applications to unbalanced and cascaded homodyning of the intracavity mode are discussed and the advantages of the latter method are shown.

quant-ph↗

arXiv2006

Characterization of unwanted noise in realistic cavities

The problem of the description of absorption and scattering losses in high-Q cavities is studied. The considerations are based on quantum noise theories, hence the unwanted noise associated with scattering and absorption is taken into account by introduction of additional damping and noise terms in the quantum Langevin equations and input--output relations. Completeness conditions for the description of the cavity models obtained in this way are studied and corresponding replacement schemes are discussed.

quant-ph↗

arXiv2006

Nonclassicality of noisy quantum states

Nonclassicality conditions for an oscillator-like system interacting with a hot thermal bath are considered. Nonclassical properties of quantum states can be conserved up to a certain temperature threshold only. In this case, affection of the thermal noise can be compensated via transformation of an observable, which tests the nonclassicality (witness function). Possibilities for experimental implementations based on unbalanced homodyning are discussed. At the same time, we demonstrate that the scheme based on balanced homodyning cannot be improved for noisy states with proposed technique and should be applied directly.

quant-ph↗

arXiv2005

Quantum-state input-output relations for absorbing cavities

The quantized electromagnetic field inside and outside an absorbing high-$Q$ cavity is studied, with special emphasis on the absorption losses in the coupling mirror and their influence on the outgoing field. Generalized operator input-output relations are derived, which are used to calculate the Wigner function of the outgoing field. To illustrate the theory, the preparation of the outgoing field in a Schrödinger cat-like state is discussed.

quant-ph↗

arXiv2005

QED of lossy cavities: operator and quantum-state input-output relations

Within the framework of exact quantization of the electromagnetic field in dispersing and absorbing media the input-output problem of a high-$Q$ cavity is studied, with special emphasis on the absorption losses in the coupling mirror. As expected, the cavity modes are found to obey quantum Langevin equations, which could be also obtained from quantum noise theories, by appropriately coupling the cavity modes to dissipative systems, including the effect of the mirror-assisted absorption losses. On the contrary, the operator input-output relations obtained in this way would be incomplete in general, as the exact calculation shows. On the basis of the operator input-output relations the problem of extracting the quantum state of an initially excited cavity mode is studied and input-output relations for the $s$-parameterized phase-space function are derived, with special emphasis on the relation between the Wigner functions of the quantum states of the outgoing field and the cavity field.

quant-ph↗

arXiv2004

Quantum Phase Space in Relativistic Theory: the Case of Charge-Invariant Observables

Mathematical method of quantum phase space is very useful in physical applications like quantum optics and non-relativistic quantum mechanics. However, attempts to generalize it for the relativistic case lead to some difficulties. One of problems is band structure of energy spectrum for a relativistic particle. This corresponds to an internal degree of freedom, so-called charge variable. In physical problems we often deal with such of dynamical variables that do not depend on this degree of freedom. These are position, momentum, and any combination of them. Restricting our consideration to this kind of observables we propose the relativistic Weyl--Wigner--Moyal formalism that contains some surprising differences from its non-relativistic counterpart.

quant-ph↗

arXiv2004

Quantum-state extraction from high-Q cavities

The problem of extraction of a single-mode quantum state from a high-Q cavity is studied for the case in which the time of preparation of the quantum state of the cavity mode is short compared with its decay time. The temporal evolution of the quantum state of the field escaping from the cavity is calculated in terms of phase-space functions. A general condition is derived under which the quantum state of the pulse built up outside the cavity is a nearly perfect copy of the quantum state the cavity field was initially prepared in. The results show that unwanted losses prevent the realization of a nearly perfect extraction of nonclassical quantum states from high-Q optical microcavities with presently available technology.

quant-ph↗

arXiv2002

Relativistic coherent states and charge structure of the coordinate and momentum operators

We consider relativistic coherent states for a spin-0 charged particle that satisfy the next additional requirements: (i) the expected values of the standard coordinate and momentum operators are uniquely related to the real and imaginary parts of the coherent state parameter; (ii) these states contain only one charge component. Three cases are considered: free particle, relativistic rotator, and particle in a constant homogeneous magnetic field. For the rotational motion of the two latter cases, such a description leads to the appearance of the so-called nonlinear coherent states.

quant-ph↗

arXiv2002

Scalar charged particle in Weyl--Wigner--Moyal phase space. Constant magnetic field

A relativistic phase-space representation for a class of observables with matrix-valued Weyl symbols proportional to the identity matrix (charge-invariant observables)is proposed. We take into account the nontrivial charge structure of the position and momentum operators. The evolution equation coincides with its analog in relativistic quantum mechanics with nonlocal Hamiltonian under conditions where particle-pair creation does not take place (free particle and constant magnetic field). The differences in the equations are connected with peculiarities of the constraints on the initial conditions. An effective increase in coherence between eigenstates of the Hamiltonian is found and possibilities of its experimental observation are discussed.

quant-ph↗

arXiv2002

Phase space localization of a scalar charged particle

The thesis is devoted to the phase space representation of relativistic quantum mechanics. For a class of observables with matrix-valued Weyl symbols proportional to the identity matrix, the Weyl-Wigner-Moyal formalism is proposed. The evolution equations are found to coincide with their counterparts in relativistic quantum mechanics with non-local Hamiltonian. The difference between the theories is connected with peculiarities of the constraints on the initial conditions. Effective increase in coherence between eigenstates of the Hamiltonian is found. Relativistic coherent states that take into account a non-trivial charge structure of the position and momentum operators and satisfy the charge superselection rule are considered. On this basis, the entangled coherent states are developed.

quant-ph↗

arXiv2001

Possible peculiarities of synchrotron radiation in a strong magnetic field

Relativistic quantum effects on physical observables of scalar charged particles are studied. Possible peculiarities of their behavior that can be verified in an experiment can confirm several fundamental conceptions of quantum mechanics. For observables independent of charge variable, we propose relativistic Wigner function formalism that contains explicitly the measurement device frame. This approach can provide the description of charged particles gas (plasma). It differs from the traditional one but is consistent with the Copenhagen interpretation of quantum mechanics. The effects that are connected with this approach can be observed in astrophysical objects - neutron stars.

quant-ph↗

arXiv2001

Relativistic Wigner Function, Charge Variable and Structure of Position Operator

The relativistic phase-space representation by means of the usual position and momentum operators for a class of observables with Weyl symbols independent of charge variable (i.e. with any combination of position and momentum) is proposed. The dynamical equation coincides with its analogue in the non-local theory (generalization of the Newton-Wigner position operator approach) under conditions when particles creation is impossible. Differences reveal themselves in specific constraints on possible initial conditions.

quant-ph↗

arXiv2001

Peculiarities of the Weyl - Wigner - Moyal formalism for scalar charged particles

A description of scalar charged particles, based on the Feshbach-Villars formalism, is proposed. Particles are described by an object that is a Wigner function in usual coordinates and momenta and a density matrix in the charge variable. It is possible to introduce the usual Wigner function for a large class of dynamical variables. Such an approach explicitly contains a measuring device frame. From our point of view it corresponds to the Copenhagen interpretation of quantum mechanics. It is shown how physical properties of such particles depend on the definition of the coordinate operator. The evolution equation for the Wigner function of a single-charge state in the classical limit coincides with the Liouville equation. Localization peculiarities manifest themselves in specific constraints on possible initial conditions.

quant-ph↗