Vacuum Reservoir Research Articles

Incomplete spontaneous decay in a waveguide caused by polarization selection

Spontaneous decay of an excited atom in a waveguide is essentially modified by the spatial structure of vacuum reservoir. This is particularly exciting in view of a range of applications for quantum information science. We found out that spontaneous decay can be incomplete, so the time dependence of the excited state population asymptotically approaches to a nonzero value, under the conditions when the atomic transition frequency is larger than the cutoff frequency of a waveguide and far from the vicinities of the cut-offs. Discovered effect is explained by the emergence of the dark state, which is non-decaying due to polarization selection rules. It was revealed for single-mode waveguide with rectangular cross section both in single-atom case and diatomic case when the long-range dipole-dipole interaction plays a significant role.

Externally induced entanglement amplification in a coherently pumped emission of laser with parametric amplifier and coupled to squeezed vacuum reservoir

Externally induced entanglement amplification in a coherently pumped Correlated Emission Laser (CEL) with parametric amplifier and coupled to a squeezed vacuum reservoir is presented. The combination of the master equation and stochastic differential equation is applied to investigate the entanglement of the correlated two photons generated by the quantum system. The resulting solutions of the correlation properties of noise forces associated with the normal ordering are used to find the mean photon number of the separate cavity modes and their correlation, EPR-pair variables, and smallest eigenvalue of the sympectic matrix. It is found that pumping atoms from the lower energy state to excited state results in a strong entanglement that remains in its maximum strength over a wide range of the strong classical pumping radiation. The introduction of the nonlinear crystal into the laser cavity, and coupling the system to the two-mode squeezed vacuum environment lead to a significant enhancement of entangled cavity light. The entanglement produced is quantified employing logarithmic negativity, Hillary Zubairy and Duan et al criteria. It has been observed that an intense light can be produced where the entanglement is strong. The amount of the entanglement produced is found to be 87% by both Duan et al and logarithmic negativity criteria.

Entanglement Quantification of Correlated Photons Generated by Three-Level Laser with Parametric Amplifier and Coupled to a Two-Mode Vacuum Reservoir

In this paper, the detailed inseparability criteria of entanglement quantification of correlated two-mode light generated by a three-level laser with a coherently driven parametric amplifier and coupled to a two-mode vacuum reservoir is thoroughly analyzed. Using the master equation, we obtain the stochastic differential equation and the correlation properties of the noise forces associated with the normal ordering. Next, we study the squeezing and the photon entanglement by considering different inseparability criteria. The various criteria of entanglement used in this paper show that the light generated by the quantum optical system is entangled and the amount of entanglement is amplified by introducing the parametric amplifier into the laser cavity and manipulating the linear gain coefficient.

The Noise Effect of Vacuum Reservoir on the Dynamics of Three-Level Laser Pumped by Coherent Light

We have investigated the effects of vacuum reservoir noise on the photon statistics and quadrature squeezing of light generated by a three-level laser pumped by coherent light and coupled to a vacuum reservoir via a single-port mirror. We have found that the effect of the vacuum reservoir noise is to increase the photon number variance and to decrease the quadrature squeezing. However, the vacuum reservoir noise has no effect on the mean photon number.

Spontaneous Emission by Three-level Atoms Pumped by Electron Bombardment

In this paper we have studied the statistical and squeezing properties of the cavity light generated by a three-level laser. In this quantum optical system, N three-level atoms available in an open cavity, coupled to a two-mode vacuum reservoir, are pumped to the top level by means of electron bombardment at constant rate. We have considered the case in which the three-level atoms and the cavity modes interact with the two-mode vacuum reservoir. We have carried out our analysis by putting the noise operators associated with the vacuum reservoir in normal order. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, we have calculated the mean and variance of the photon number as well as the quadrature squeezing for the cavity light. In addition, we have shown that the presence of the spontaneous emission process leads to a decrease in the mean and variance of the photon number. We have observed that the two-mode cavity light is in a squeezed state and the squeezing occurs in the minus quadrature. The maximum quadrature squeezing of the light generated by the laser, operating far below threshold, is found to be 50% below the vacuum-state level. We have also established that the mean photon number in the presence of spontaneous emission is less than the absence of spontaneous emission.

Control of quantum correlation of high dimensional system in squeezed vacuum reservoir

We study the quantum correlation and entanglement for a high-dimensional spin-S system in a squeezed vacuum reservoir. The exact analytical solution is presented, which shows that the decoherence function governs the quantum correlation and quantum entanglement of corresponding dynamical process. The squeezed amplitude parameter for quantum correlation and quantum entanglement has a negative impact in the whole process, the better the squeezing effect, the greater the negative impact. Furthermore, in the super-Ohmic reservoir, the influence of Ohmic parameter on quantum correlation and quantum entanglement can be divided into two regions in terms of the critical value s=2.5⁡. If s<2.5, the decay rate of quantum correlation slows down obviously, and the environmental decoherence effect is much smaller than that of Ohmic and sub-Ohmic reservoirs. On the contrary, if s>2.5, the decay rate of quantum correlation accelerates obviously, and the decoherence effect surpasses the cases of Ohmic and sub-Ohmic reservoirs greatly.

Steady-state population inversion of multiple Ξ -type atoms by the squeezed vacuum in a waveguide

We study the dynamics of multiple $\mathrm{\ensuremath{\Xi}}$-type atoms driven by a squeezed vacuum reservoir in a quasi-one-dimensional waveguide. We show that the atomic system's steady state is a pure state, and a complete population inversion can occur when the dipole moment of the second transition is almost perpendicular to the polarization of the incident squeezed light. We also prove that the steady state of the system is the direct product of that in the single-atom case with modified squeezed vacuum even when dipole-dipole interaction is involved. This steady-state population inversion may be used to study the two-photon laser or collective atomic effect.

Perfect squeezing of terahertz light by two quantum wells using a squeezed vacuum reservoir: erratum

Perfect squeezing of terahertz light by two quantum wells using a squeezed vacuum reservoir: erratum

Theory of quantum entanglement of intra-cavity photons produced by a non-degenerate parametric oscillator (NDPO); Semi-classical approach

The von-Neumann entropy (VNE) which is usually expressed in terms of the density operator is the mathematical tool to measure the degree of entanglement of a bi-partite system. Applying the solutions of the quantum Langevin equations, the anti-normally ordered characteristic function of the intra-cavity photons produced by a non-degenerate parametric oscillator is calculated. With the help of the resulting characteristic function, the Q function which is then used to calculate the entanglement of the intra-cavity photons using VNE is determined. Moreover, the photon number distribution of the intra-cavity photons produced by a non-degenerate parametric oscillator coupled to a two-mode squeezed vacuum reservoir is determined.

Energy transfer, correlations and decoherence in a dimer in terms of the two-level atomic distances

In this manuscript, we study the coherent single-excitation energy transfer for a dimer system consisting of a donor and an acceptor modeled by two-level systems (TLSs), which are immersed in common thermal environment. We illustrate the effects of the distance between TLSs and temperature of the thermal reservoir on the energy transfer process considering collective damping and dipole–dipole interaction. Concretely, the control and enhancement of the probability during the time evolution is performed by a suitable choice of the distance between TLSs with respect to the temperature of the reservoir. On the other hand, we study the time evolution of the quantum and classical correlations of the TLSs-state through calculating concurrence and quantum discord. We find that the dynamical behavior of quantum and classical correlations dynamics in thermal reservoir is similar to vacuum reservoir with slight decrease in the amount of correlations. These correlations are also very sensitive to the TLSs-distance and when the distance becomes significantly large, the amount of correlations exponentially decrease with the time. Finally, we explore the relationship between the probability and correlations during the evolution and shows that quantum and classical correlations can be created during the process of excitation energy transfer.

Quantum Interference Effects on Information Phase Space and Entropy Squeezing.

Wehrl entropy and its density are used to investigate the dynamics of loss of coherence and information in a phase space for an atomic model of two-photon two-level atom coupled to different radiation reservoirs (namely, normal vacuum (NV), thermal field (TF) and squeezed vacuum (SV) reservoirs). Particularly, quantum interference (QI) effect, due to the 2-photon transition decay channels, has a paramount role in: (i) the atomic inversion decay in the NV case, which behaves as quantum Zeno and anti-Zeno decay effect; (ii) the coherence and information loss in the phase space; and (iii) identifying temporal information entropy squeezing. Results are also sensitive to the initial atomic state.

Perfect squeezing of terahertz light by two quantum wells using a squeezed vacuum reservoir

The nonclassical properties of a microcavity confining two quantum wells irradiated by a coherent light source and interacting with a squeezed vacuum reservoir are investigated. By deriving analytical expressions of the intensity power spectrum, the squeezing spectrum, and the second-order correlation function of the output field, we show that the proposed scheme generates perfect squeezing. The obtained results are quite different from the single-quantum-well cavity system where, under the same conditions, squeezing does not exceed 50%, and the transmitted light is bunched. It turns out that the presence of indirect excitons in the cavity strongly modifies the quantum dynamics of the system.

Dynamics of Two-level Atom Interaction with Single-mode Field

In this paper, we investigate the dynamics of fluorescent light emitted by a two-level atom interacts with squeezed vacuum reservoir is studied wisely using two-time correlation function and the master equation fundamentals approaches. We use the pertinent master equation to calculate the time-evolution of cavity filed operators as well as two-time correlation function. The mathematical analysis shows the fluorescent spectrum of light emitted by the atom is turned out to be a single peak at a Lorentz's frequency for both squeezed vacuum reservoir and thermal reservoir. On the other hand, we have identified that the squeezed vacuum reservoir input is responsible to the stimulated emission of photons from the atom. Moreover, it is identified that thermal reservoir is more efficient than squeezed vacuum reservoir to have valuable power spectrum. The power spectrum which characterizes the fluorescent light generated by a two-level atom has been summered as it is observed for both case; (i) when a two-level atom coupled to squeezed vacuum reservoir and (ii) when the two-level atom coupled to thermal reservoir. Finally, we generalized from the paper is that the power spectrum of generated light from a two-level atom coupled to thermal reservoir is greater than the power spectrum generated from a two-level atom coupled to squeezed vacuum reservoir. In contrast, more stimulated and squeezed photons are emitted in the case when the atom is coupled with squeezed vacuum reservoir.

The Quantum analysis of Nondegenerate Three-Level Laser with Spontaneous Emission and Noiseless Vacuum Reservoir

The analysis of quantum properties of the cavity light produced by a coherently driven nondegenerate three-level laser possessing an open cavity and coupled to a two-mode vacuum reservoir is presented. The normal ordering of noise operators associated with the vacuum reservoir is considered. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, the squeezing properties, entanglement amplification, and the normalized second-order correlation function of the cavity radiation are described. The three-level laser generates squeezed light under certain conditions, with maximum intracavity squeezing being 50% below the vacuum-state level. Moreover, it is found that the presence of spontaneous emission increases the quadrature squeezing and entanglement and decreses the mean photon number of the two-mode cavity radiation.

Investigations on quantum-memory-assisted entropic uncertainty relation between coupled qubits in squeezed vacuum reservoir

We investigate the quantum-memory-assisted entropic uncertainty relation between coupled qubits which are initially in entangled mixed states in squeezed vacuum reservoir. We find that the uncertainty of quantum system is dependent on the squeezing effect of optical field. In the squeezed vacuum reservoir, the smaller the squeezed amplitude parameter is, the smaller the entropic uncertainties and its lower bound are, the more favorable to improve the accuracy of quantum measurement. Through optimizing the parameters of the initial quantum state, the measurement precision of observable mechanical quantity can be improved. In particular, when the relative phase of the initial quantum state is an integer multiple of ⁡π, the lower bound of the entropic uncertainty reaches a minimum.

Enhancement of Squeezing and Entanglement in a Non-Degenerate Three-Level Cascade Laser with Coherently Driven Cavity

We study a nondegenerate three-level cascade laser coupled to a two-mode vacuum reservoir, by employing the stochastic differential equations associated with the normal ordering. The amplification of the properties of squeezing and entanglement of the cavity light is investigated. We have found that there is an entanglement between the states of the light generated in the cavity, due to the strong correlation of the light emitted, when the atom decays from the top level to the bottom level via the intermediate one. We have also obtained that the two cavity modes are strongly entangled, and the degree of entanglement is directly related to the two-mode squeezing.

Two-Level Atom with Squeezed Light from Optical Parametric Oscillators

The dynamics of a coherently driven two-level atom with parametric amplifier and coupled to a vacuum reservoir is analyzed. The combination of the master equation and the quantum Langevin equation is presented to study the quantum properties of light. By using these equations, we have determined the time evolution of the expectation values of the cavity mode and atomic operators. Moreover, with the aid of these results, the correlation properties of noise operators, and the large-time approximation scheme, we calculate the mean photon number, power spectrum, second-order correlation function, and quadrature variances for the cavity-mode light and fluorescence. It is found that the half-width of the power spectrum for the fluorescent light in the presence of a parametric amplifier increases, while it decreases for the cavity-mode light. Moreover, we have found the probability for the atom to be in the upper level in the presence of a parametric amplifier.

Quantum squeezing in a modulated optomechanical system.

Quantum squeezing, as a typical quantum effect, is an important resource for many applications in quantum technologies. Here we propose a scheme for generating quantum squeezing, including the ponderomotive squeezing and the mechanical squeezing, in an optomechanical system, in which the radiation-pressure coupling and the mechanical spring constant are modulated periodically. In this system, the radiation-pressure interaction can be enhanced remarkably by the modulation-induced mechanical parametric amplification. Moreover, the effective phonon noise can be suppressed completely by introducing a squeezed vacuum reservoir. This ultimately leads to that our scheme can achieve a controllable quantum squeezing. Numerical calculations show that our scheme is experimentally realizable with current technologies.

Enhanced photon-phonon cross-Kerr nonlinearity with two-photon driving.

We propose a scheme to significantly enhance the cross-Kerr (CK) nonlinearity between photons and phonons in a quadratically coupled optomechanical system (OMS) with two-photon driving. This CK nonlinear enhancement originates from the parametric-driving-induced squeezing and the underlying nonlinear optomechanical interaction. Moreover, the noise of the squeezed mode can be suppressed completely by introducing a squeezed vacuum reservoir. As a result of this dramatic nonlinear enhancement and the suppressed noise, we demonstrate the feasibility of the quantum nondemolition measurement of the phonon number in an originally weak coupled OMS. In addition, the photon-phonon blockade phenomenon is also investigated in this regime, which allows for performing manipulations between photons and phonons. This Letter offers a promising route towards the potential application for the OMS in quantum information processing and quantum networks.

Waveguide quantum electrodynamics in squeezed vacuum

We study the dynamics of a general multiemitter system coupled to the squeezed vacuum reservoir and derive a master equation for this system based on the Weisskopf-Wigner approximation. In this theory, we include the effect of positions of the squeezing sources which is usually neglected in the previous studies. We apply this theory to a quasi-one-dimensional waveguide case where the squeezing in one dimension is experimentally achievable. We show that while dipole-dipole interaction induced by ordinary vacuum depends on the emitter separation, the two-photon process due to the squeezed vacuum depends on the positions of the emitters with respect to the squeezing sources. The dephasing rate, decay rate, and the resonance fluorescence of the waveguide-QED in the squeezed vacuum are controllable by changing the positions of emitters. Furthermore, we demonstrate that the stationary maximum entangled NOON state for identical emitters can be reached with arbitrary initial state when the center-of-mass position of the emitters satisfies certain conditions.