A. V. Dodonov

Rabi model beyond the rotating-wave approximation: Generation of photons from vacuum through decoherence

We study numerically the dynamics of the Rabi Hamiltonian, which describes the interaction of a single cavity mode and a two-level atom without the rotating wave approximation. We analyze this system subjected to damping and dephasing reservoirs, included via the usual Lindblad superoperators in the master equation. We show that the combination of the antirotating term and the atomic dephasing leads to linear asymptotic photon generation from the vacuum. We reveal the origins of the phenomenon and estimate its importance in realistic situations.

Photon generation from vacuum in nondegenerate cavities with regular and random periodic displacements of boundaries

We study the influence of fluctuations in periodic motion of boundaries of an ideal three-dimensional cavity on the rate of photon generation from vacuum due to the nonstationary Casimir effect.

Nonstationary Casimir effect in cavities with two resonantly coupled modes

We study the peculiarities of the nonstationary Casimir effect (creation of photons in cavities with moving boundaries) in the special case of two resonantly coupled modes with frequencies ω0 and (3 + ∆)ω0, parametrically excited due to small amplitude oscillations of the ideal cavity wall at the frequency 2 ω0(1 + δ) (with |δ|, |∆ |� 1). The effects of thermally induced oscillations in time dependences of the mean numbers of created photons and the exchange of quantum purities between the modes are discovered. Squeezing and photon distributions in each modes are calculated for initial vacuum and thermal states. A possibility of compensation of detunings is shown.  2001 Elsevier Science B.V. All rights reserved.

QED effects in a cavity with a time-dependent thin semiconductor slab excited by laser pulses

We consider the problem of the creation of quanta of an electromagnetic field from the initial vacuum (or thermal) state in a closed high-Q cavity due to periodical variations of conductivity of a thin semiconductor boundary layer excited by short laser pulses. Fast changes of conductivity from practically a zero value to a high one and then again to zero simulate periodical displacements of the cavity wall. This scheme has been chosen to model the non-stationary Casimir effect in the experiment which is under preparation at Padua University. We provide analytical and numerical evaluations for the number of photons which could be created under realistic experimental conditions. We show the importance of taking into account intrinsic losses in the semiconductor slab caused by the finite conductivity during the intermediate part of the excitation– recombination cycle. We analyse the influence of different parameters, such as the diffusion and mobility coefficients of carriers, surface recombination velocity, absorption coefficient of laser radiation, thickness of the slab and geometry of the cavity. We conclude that a significant amount (>10 3 ) of ‘Casimir photons’ with a frequency of 2.5 GHz can be produced from vacuum in a cavity with dimensions of the order of 10 cm, if one can arrange several thousand strongly periodical laser pulses with a duration of the order of 1 ps, periodicity close to 200 ps and energy ∼10 −3 J, illuminating the semiconductor slab of thickness ∼1 mm and the mobility ∼ 1m 2 V −1 s −1 , provided the recombination time can be reduced below the critical value ∼30 ps.

The nonstationary Casimir effect in a cavity with periodical time-dependent conductivity of a semiconductor mirror

We consider the problem of photon creation from vacuum or thermal states inside a cavity with periodical time-dependent conductivity of a thin semiconductor boundary layer, simulating periodical displacements of the wall. Our approach is based on the consistent model of a quantum-damped harmonic oscillator with arbitrary time-dependent frequency and damping coefficients in the framework of the Heisenberg–Langevin equations with two noncommuting delta-correlated noise operators. We calculate the rate of photon generation under the resonance conditions, taking into account the internal dissipation inside the semiconductor. This rate depends mainly on two parameters: the total intensity of the laser pulse and the recombination time of photo-excited carriers in the semiconductor slab (for fixed mobility of carriers and geometry). Optimal values of these parameters and dimensions of the cavity are found for the TE and TM modes. The influence of temperature and detuning from strict resonance is analysed.

Resonance generation of photons from vacuum in cavities due to strong periodical changes of conductivity in a thin semiconductor boundary layer

We study a possibility of photon generation from vacuum in a cavity with an artificial effective time-dependent plasma mirror, which could be created by mean so fp eriodical short laser pulses, illuminating a thin semiconductor slab .W et ak ei nto account two important circumstances: a big imaginary part of the complex time-dependent dielectric permeability inside the slab and a strong dependence of this imaginary part on the distance from the surface of the slab. We find the conditions under which the usual unitary quantization schemes in time-dependent media with real dielectric permeability can be applied to the problem concerned with relatively small (a few per cent) error. We show that, by using a slab with thickness of the order of 1 mm, it is possible to generate a large number of microwave (GHz) photons (up to 10 8 or more) after several thousand picosecond pulses with repetition frequency of the order of 1 GHz, provided that semiconductor materials with high mobility of carriers, high photoabsorption efficiency and smal lr ecombination time (less than 1 ns) can be found. We discuss the possible advantages of modes with TM polarization over TE ones, as well as some other important problems to be solved.

Inclusion of nonidealities in the continuous photodetection model

Some nonideal effects as nonunit quantum efficiency, dark counts, dead time, and cavity losses that occur in experiments are incorporated within the continuous photodetection model by using the analytical quantum trajectories approach. We show that in standard photocounting experiments the validity of the model can be verified and the formal expression for the quantum jump superoperator can also be checked.

Engineering quantum jump superoperators for single-photon detectors

We study the back action of a single-photon detector on the electromagnetic field upon a photodetection by considering a microscopic model in which the detector is constituted of a sensor and an amplification mechanism. Using the quantum trajectories approach we determine the quantum jump superoperator (QJS) that describes the action of the detector on the field state immediately after the photocount. The resulting QJS consists of two parts: the bright-count term, representing the real photoabsorptions, and the dark-count term, representing the amplification of intrinsic excitations inside the detector. First we compare our results for the counting rates to experimental data, showing good agreement. Then we point out that by modifying the field frequency one can engineer the form of the QJS, obtaining the QJSs proposed previously in an ad hoc manner.

Entanglement of Resonantly Coupled Field Modes in Cavities with Vibrating Boundaries

We study time dependence of various measures of entanglement (covariance entanglement coefficient, purity entanglement coefficient, normalized distance coefficient, entropy coefficients) between resonantly coupled modes of the electromagnetic field in ideal cavities with oscillating boundaries. Two types of cavities are considered — a three-dimensional cavity possessing eigenfrequencies ω3 = 3ω1, whose wall oscillates at the frequency ωw = 2ω1, and a one-dimensional (Fabry–Perot) cavity with an equidistant spectrum ωn = nω1 where the distance between perfect mirrors oscillates at the frequencies ω1 and 2ω1. The behavior of entanglement measures in these cases turns out to be completely different, although all three coefficients demonstrate qualitatively similar time dependences in each case (except some specific situations where the covariance entanglement coefficient based on traces of covariance submatrices seems to be essentially more sensitive to entanglement than other measures, which are based on determinants of covariance submatrices). Different initial states of the field, namely, vacuum, squeezed vacuum, thermal, Fock, and even/odd coherent states, are considered.

Smooth quantum-classical transition in photon subtraction and addition processes

Recently Parigi et al. [Science 317, 1890 (2007)] implemented experimentally the photon subtraction and addition processes from and to a light field in a conditional way, when the required operations were produced successfully only upon the positive outcome of a separate measurement. It was verified that for a low-intensity beam (quantum regime) the bosonic annihilation operator