Quantum Optics

We study the dynamics of a ∨-type three-level atom in the cavity employing the dressed state of the system. We consider a ∨-type three-level atom initially in a different state that interacts with two mode photons in a closed cavity. The initial state of the atom and Rabi frequency have a significant effect on the population exchange between excited and ground levels. The numerical results show that the atom-field coupling strength determines the fast and slow periodic oscillation of the probability between the upper and ground states. The highest probability of finding it in the upper and ground states is determined by the initial state conditions of the atom. In general, the initial state conditions of the atom and the atom-field coupling strength have a significant effect on population transfer between the upper and ground states of a ∨-type three-level atom.

Constructing an estimator for functional estimation is one of the problems in statistical inference. In this paper, the problem of constructing an estimator for a studentized sum is considered in the nonparametric set-up. In this set-up, data are used to infer to an unknown quantity while making as few assumptions as possible. This non-smooth functional lack some degree of properties traditionally relied upon in estimation. Smooth functionals converge at the rate of n 1 2 while non-smooth functionals converge at the rate slower than n 1 2 . This highlights the reason why standard techniques fail to give sharp results. A clear and accurate approximation is obtained by using an approximation that admits cumulant generating function; saddle point approximation. An optimal estimator is obtained using the MiniMax criterion where the lower and upper bounds are constructed. While working in the context of MiniMax estimation, the lower bounds are most important. The MiniMax lower bound is o...

We demonstrate an optical method to engineer optical Schrodinger cat states (SCSs) of large amplitude in the range from 2 to 3 with high fidelity close to 0.99. The approach uses the {\alpha}-representation of the SCSs in infinite Hilbert with base displaced number states characterized by the displacement amplitude {\alpha}. An arbitrary {\alpha}-representation of SCSs enables to manipulate the amplitudes in wider range of parameters that which greatly expands the possibilities for generation of the states. We consider a general optical scheme for implementation of the conditioned states close to SCSs with linear optics methods and detectors projecting unitarily transformed initial state onto target. Different input states (number and coherent states, Schrodinger kitten states) are selected as input.

I have classified motions into four types: Perfect Motion (PM), Normal motion (NM), Freefall Motion (FM) and Stubborn Motion (SM), and made three different formulas for those types of Motions: MV for Perfect Motion, n(MV) for Normal Motion and MV 2 for Freefall Motion and Stubborn Motion. E=MC 2 is the quantity of work required to accelerate a body of mass M to the speed C in Stubborn Motion, and not the Mass-Energy Equivalence Formula as Einstein claimed.

The methods of feedback control are widely used in the modern physics, but still they are not very popular in quantum optics. What is sufficient that very often this ”cybernetical” approach does not demand to involve a very complicated physical devices and can be arranged in ...

We presen a secure direct communication protocol by using step-split Einstein-Podolsky-Rosen (EPR) pair. In this communication protocol, Alice first sends one qubit of an EPR pair to Bob. Bob sends a receipt signal to Alice through public channel when he receives Alice's first qubit. Alice performs her encoding operations on the second qubit and sends this qubit to Bob. Bob

In this paper, we study a Hamiltonian system constituted by two coupled two-level atoms (qubits) interacting with a nonlinear generalized cavity field. The nonclassical two-qubit correlation dynamics are investigated using Bures distance entanglement and local quantum Fisher information under the influences of intrinsic decoherence and qubit–qubit interaction. The effects of the superposition of two identical generalized coherent states and the initial coherent field intensity on the generated two-qubit correlations are investigated. Entanglement of sudden death and sudden birth of the Bures distance entanglement as well as the sudden changes in local Fisher information are observed. We show that the robustness, against decoherence, of the generated two-qubit correlations can be controlled by qubit–qubit coupling and the initial coherent cavity states.

Optical tomography is investigated for time-dependent quantum states, which are generated from coherent even and odd coherent cavity fields interacting with a two-level system (qubit) in the presence of phase damping. The effects of the qubit-cavity coupling, detuning, and cavity phase damping on the optical tomography distribution are studied. The dynamics of the optical tomography is explored for an open cavity field. We show an aspect of the alteration of the optical tomography distribution.

In this work, we examine a nonlinear version of the Tavis–Cummings model for two two-level atoms interacting with a single-mode field within a cavity in the context of power-law potentials. We consider the effect of the particle position that depends on the velocity and acceleration, and the coupling parameter is supposed to be time-dependent. We examine the effect of velocity and acceleration on the dynamical behavior of some quantumness measures, namely as von Neumann entropy, concurrence and Mandel parameter. We have found that the entanglement of subsystem states and the photon statistics are largely dependent on the choice of the qubit motion and power-law exponent. The obtained results present potential applications for quantum information and optics with optimal conditions.

Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity and charge density wave to, possibly, high temperature superconductivity. Their measurement in solids is subject of an intense scientific debate focused on the research of a methodology capable of establishing a direct link between the variance of the ionic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise limited regime. The variance of the time dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interactions between photonic and phononic fields unveils evidences of squeezing of thermal phonons in $\alpha-$quartz.

In this study, we control a three-level atomic system using a typical strong control field with a modified quotient double exponential form (modified QEXP). The considered atomic configuration is a V-type three-level system in which QEXP is applied between the ground and excited states. Atomic population inversion can be achieved by selecting specific shaped pulses. In addition, we control the temporal atomic coherence of the system for a spectrum of waveforms and derive both absorption and dispersion spectra. Compared to a continuous wave control field, the proposed modified QEXP pulse achieves an electromagnetically induced transparency window in the absorption spectrum.

In this work, we introduce the standard Tavis-Cummings model to describe two-qubit system interacting with a single-mode field associated to power-law (PL) potentials. We explore the effect of the time-dependent interaction and the Kerr-like medium. We solve the Schrödinger equation to obtain the density operator that allows us to investigate the dynamical behaviour of some quantumness measures, such as von Neumann entropy, negativity and Mandel’s parameter. We provide how these entanglement measures depend on the system parameters, which paves the way towards better control of entanglement generation in two-qubit systems. We find that the enhancement and preservation of the atoms-field entanglement and atom-atom entanglement can be achieved by a proper choice of the initial parameters of the field in the absence and presence of the time-dependent interaction and Kerr medium. We examine the photons distribution of the field and determine the situations for which the field exhibits super-poissonian, poissonian or sub-poissonian distribution.

We explore a superconducting charge qubit interacting with a dissipative microwave cavity field. Wigner distribution and its non-classicality are investigated analytically under the effects of the qubit–cavity interaction, the qubit–cavity detuning, and the dissipation. As the microwave cavity field is initially in an even coherent state, we investigate the non-classicality of the Wigner distributions. Partially and maximally frozen entanglement are produced by the qubit–cavity interaction, depending on detuning and cavity dissipation. It is found that the amplitudes and frequency of the Wigner distribution can be controlled by the phase space parameters, the qubit–cavity interaction and the detuning, as well as by the dissipation. The cavity dissipation reduces the non-classicality; this process can be accelerated by the detuning.

By using the Born Markovian master equation, we study the relationship among the Einstein–Podolsky–Rosen (EPR) steering, Bell nonlocality, and quantum entanglement of entangled coherent states (ECSs) under decoherence. We illustrate the dynamical behavior of the three types of correlations for various optical field strength regimes. In general, we find that correlation measurements begin at their maximum and decline over time. We find that quantum steering and nonlocality behave similarly in terms of photon number during dynamics. Furthermore, we discover that ECSs with steerability can violate the Bell inequality, and that not every ECS with Bell nonlocality is steerable. In the current work, without the memory stored in the environment, some of the initial states with maximal values of quantum steering, Bell nonlocality, and entanglement can provide a delayed loss of that value during temporal evolution, which is of interest to the current study.

In the framework of time-varying coupling and power-law potentials, we investigate quantum entanglement and quantum Fisher information in a system that consists of a three-level atom interacting with a quantized field. The results illustrate that the quantum entanglement and quantum Fisher information's temporal evolution depend critically on the physical properties of the field and its coupling to the atom. It is noteworthy to notice that the quantifiers are sensitive to the exponent parameter of the potential with and without time-varying coupling. Considerable nonlocal correlation with the accuracy of parameter estimation can be achieved through the proper control of physical parameters.

The amplitude of the electric field of a mode of the electromagnetic field is not a fixed quantity: there are always quantum mechanical fluctuations. The amplitude, having both a magnitude and a phase, is a complex number and is described by the mode annihilation operator a. It is also possible to characterize the amplitude by its real and imaginary parts which correspond to the Hermitian and anti-Hermitian parts of a, X sub 1 = 1/2(a(sup +) + a) and X sub 2 = i/2(a(sup +) - a), respectively. These operators do not commute and, as a result, obey the uncertainty relation (h = 1) delta X sub 1(delta X sub 2) greater than or = 1/4. From this relation we see that the amplitude fluctuates within an 'error box' in the complex plane whose area is at least 1/4. Coherent states, among them the vacuum state, are minimum uncertainty states with delta X sub 1 = delta X sub 2 = 1/2. A squeezed state, squeezed in the X sub 1 direction, has the property that delta X sub 1 is less than 1/2....

The Wigner quasi-probability distribution function is an important tool for estimating the quantumness of quantum states. The Wigner distribution function (WDF) is related monotonically to the coherent field state density operator and their probability distributions. In this paper, we analyze the time-dependent resonator coherent field states produced by a flux qubit's interaction with a resonator-field through a two-photon coupling. The WDF dynamics of the coherent field states is investigated under the effects of the qubitresonator detuning and the intrinsic decoherence. The WDF non-classicality associated with the mixedness resonator entropy dynamics can be controlled by varying the qubit-resonator interaction, detuning as well as the decoherence. The intrinsic decoherence clearly affects the WDF non-classicality, identified by the negative values of the WDF. Finally, by fixing one or both of the complex phase space components, we are able to explore the dynamics of the Wigner-distribution functions.

In this paper, we explore the squeezing effect generated by two coupled optical cavities. Each cavity contains a second-order nonlinear material and coherently pumped by a laser. Our results show that light intensity is strongly improved due to the presence of the nonlinearities and mainly depends on the detunings between external laser frequencies and cavity modes. More interestingly, the proposed scheme could enhance light squeezing for moderate coupling between cavities : the squeezing generated by one cavity is enhanced by the other one. For resonant interaction, highest squeezing effect is obtained near resonance. When fields are non resonant, squeezing increases near resonance of the considered cavity, but decreases for large detunings relative to the second cavity. Further, when the dissipation rate of the second cavity is smaller than the first, the squeezing could be improved, attaining nearly the perfect squeezing. While the temperature elevation has a negative impact overall on the nonclassical light, squeezing shows an appreciable resistance against thermal baths for appropriate parameter sets.

Teleported noise does not depend on the particular outcomes of the homodyne measurements when Gaussian states, operations and channels are employed. Covariance matrix (CM) of the teleported state (to Bob) is a given and deterministic function of the CM of Allice's state. It depends only on the measurement setup. Therefore, Bob can extract the noise (classical information) Alice has encoded in her state (as squeezing) by measuring the noise in his own state, vice versa. The two share the information about the measurement setup (Gaussian operations) only one time. Each of the copies teleported to Bob has a different displacement (state is not cloned) so Bob cannot measure his noise by performing a noise distribution around a given mean quadrature. However, Bob can convert the encoded squeezing into two-mode entanglement and employ it in a work-extraction process where the extracted work depends solely on the CM. Therefore, Alice can encode classical information as squeezing and Bob can read it from the amount of the extracted work in his port without further need for a classical channel. We show that the protocol does not conflict with the no-cloning and no-communication theorems. We could not manage to find a phenomenon avoiding the physical realization of the protocol. If it indeed works, it will allow communication of two ships under electromagnetic jamming or two submarines while they are in deep sea.