Correlated Emission Laser Research Articles

Entanglement of mechanical modes in a doubly resonant optomechanical cavity of a correlated emission laser

We explore the extent of the induced entanglement of the mechanical modes that can be attributed to the transfer of coherence from two-mode cavity radiation in a doubly resonant optomechanical cavity. It is expected that this scheme can support a generation of mechanical oscillations with a robust degree of entanglement combined with significant controllability. The entanglement is found to be sensitive to the specific choices of the frequencies of the bichromatic drive laser. It also turns out that the degree of entanglement would be enhanced with increasing rates of injection of the atoms but with decreasing initial lengths of a doubly resonant cavity and atomic decay rates. In addition, the entanglement is found to behave qualitatively in the same way for the measures of entanglement we have applied. Since the scheme we considered can possibly be implemented with current technology and allows the quantum features of cavity radiation to be accessible for application, we anticipate that it can be utilized in the realization of continuous-variable quantum information processing.

Effects of a three-level laser on mechanical squeezing in a doubly resonant optomechanical cavity coupled to biased noise fluctuations

We address the behavior of squeezing in two movable mirrors coupled to a pumped correlated emission laser inside a doubly resonant optomechanical driven cavity in the presence of biased noise fluctuations. Aiming at generating controllable and robust mechanical squeezing that can be utilized in making the quantum features of radiation in the cavity accessible for application, we explore mechanical squeezing that can be induced as a result of the transfer of coherent superposition. We found that a coupled mechanical oscillator mode exhibits squeezing in the good cavity limit and adiabatic regime. It is also shown that the degree of mechanical squeezing is robust for large amplitudes of atomic pumping until maximum squeezing is achieved but weakens afterwards. The squeezing turns out to be powerful mainly for strong atom-field coupling, large atomic injection rates, and intense biased noise fluctuations. In light of the observed possibility of controlling the realizable degree of squeezing, we hope and expect that the considered system could be employed in applications such as quantum metrology.

Nonclassical Features of Intra-Cavity and Transmitted Fields in a Coherently-Pumped Correlated-Emission Laser with Injected Thermal Light†

Nonclassical Features of Intra-Cavity and Transmitted Fields in a Coherently-Pumped Correlated-Emission Laser with Injected Thermal Light†

Dynamics of the Cavity Radiation of a Correlated Emis-sion Laser Coupled to a Two-Mode Thermal Reservoir

In this paper, the quantum properties of the cavity light beam produced by a coherently driven nondegenerate three-level laser with an open cavity and coupled to a two-mode thermal reservoir are thoroughly analyzed. We have carried out our analysis by putting the noise operators associated with the thermal reservoir in normal order. Here we discussed more the effect of thermal light and the spontaneous emission on the dynamics of the quantum processes. It is found that the maximum degree of intracavity squeezing 43% below the vacuum-state level. Moreover, the presence of thermal light leads to decrease the degree of entanglement.

Quantum properties of correlated emission laser with dephasing and phase fluctuation

We consider a two-photon laser in a cascade configuration coupled to an ordinary vacuum reservoir via a partially transmitting mirror. The impacts of the dephasing and the phase fluctuation on the entanglement, two-mode squeezing, and the intensity of the intracavity radiation are studied at steady-state. It so happens that the initial atomic coherence is the cause for the quantum properties of the cavity radiation even in the presence of the decoherence. We show that the dephasing rates and the phase fluctuations hurt the amount of squeezing and entanglement of the intracavity radiation. However, the dephasing rate leads to an increase in the intensity of the cavity radiation. Moreover, the phase fluctuation degrades the intensity of the intracavity radiation near to the initial maximum atomic coherence and it enhances otherwise.

Tunable quantum and statistical features of the two-mode radiation generated by a correlated emission laser injected with squeezed radiation

The role of phase fluctuation on the quantum and statistical features of the two-mode radiation produced by a correlated emission laser which is externally injected with squeezed radiation is discussed. The considered atoms are prepared in the ground and excited states with equal probabilities before being injected into the laser cavity, and an external coherent field generates the atomic coherence that leads to the non-classical features in the quantum system. A non-degenerate parametric amplifier is also introduced into the laser cavity which is coupled to a two-mode squeezed environment. It is found that the quantum and statistical properties are very sensitive to and highly altered by the phase fluctuation when the strength of the external coherent field is weak. On the contrary, the external coherent field entirely overcomes the influence of phase fluctuation for the amplitude of the external coherent field that lies in the strong pumping regime so that the strength of squeezing and entanglement, and photon statistics of the two-mode radiation are not substantially affected by the phase fluctuation.

Continuous-Variable Entanglement Adjustable by Phase Fluctuation and Classical Pumping Field in a Correlated Emission Laser Seeded with Squeezed Light

We present the influence of phase fluctuations on the entanglement and intensity of the radiation produced by a correlated-emission laser. The three-level atoms are initially prepared in a partial coherent superposition of the ground and exited states, and the driven radiation field incoming via the input mirror induces the atomic coherence that leads to the entanglement in the quantum system. The laser cavity also contains a nondegenerate parametric amplifier and is seeded by a two-mode squeezed light. The entanglement is analyzed by applying the Duan–Giedke–Cirac–Zoller (DGCZ) and logarithmic negativity inseparability criteria for a continuous variable system. We find that the phase fluctuation remarkably reduces the amount of entanglement in the weak driving field. On the other hand, the driven field completely overcomes the influence of phase fluctuations in the strong driving field, so that the entanglement remains in its highest degree (97%) in this regime.

A Bright Entanglement and Squeezing Generated by an External Pumping Radiation in a Correlated Emission Laser

The quantum and statistical properties of light generated by an external classical field in a correlated emission laser with a parametric amplifier and coupled to a squeezed vacuum reservoir are investigated using the combination of the master and stochastic differential equations. First, the solutions of the cavity-mode variables and correlation properties of noise forces associated to the normal ordering are obtained. Next, applying the resulting solutions, the mean photon number of the separate cavity modes and their crosscorrelation, smallest eigenvalue of the symplectic matrix, mean photon number, intensity difference fluctuation, photon number variance, and intensity correlation are derived for the cavity-mode radiation. The entanglement produced is studied employing the logarithmic negativity criterion. It is found that pumping atoms from the lower energy state to excited state, introducing the nonlinear crystal into the cavity and coupling the system to a biased noise fluctuation, generate a bright and strong squeezing and entanglement with enhanced statistical properties although the atoms are initially in the ground state.

Dynamics of a Nondegenerate Three-Level Laser with Parametric Amplifier and Coupled to a Two-Mode Squeezed Vacuum Reservoir

In this paper, the effect of a squeezed parameter and parametric amplifier on squeezing and entanglement of a correlated emission laser is thoroughly analyzed. The combination of the master equation and stochastic differential equation is presented to study the quantum features of the light. Moreover, with the aid of the resulting solutions together with the correlation properties of noise operators, the quadrature squeezing and entanglement and the mean number of photon pairs of the cavity light are determined. It is found that a large amplitude of the classical driving radiation induces a strong correlation between the top and bottom states of three-level atoms to produce a high degree of squeezing and entanglement. Furthermore, the presence of parametric amplifier and squeezed parameter is found to enhance the degree of squeezing and entanglement of the cavity light.

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.

One-way Einstein–Podolsky–Rosen steering with the aid of the thermal noise in a correlated emission laser

We present to use the thermal noise as an effective way to manipulate the direction of Einstein–Podolsky–Rosen (EPR) steering. In particular, a system of three-level cascade laser is under our consideration, in which the atoms are prepared in an initial superposition of the upper excited level and ground level and the cavity modes are damped by the thermal bath. It is found that the thermal noise plays a constructive role in realizing the one-way EPR steering and expanding the parameter region of the steady-state asymmetric steering. In the absence of the thermal noise, two-way steering mainly occurs due to the injected atomic coherence that is quite helpful for entanglement enhancement. Surprisingly, when the thermal noise is involved, the one-way steering substitutes for two-way steering and it can be obtainable in most parameter region. Actually, the thermal noise significantly increases the mean number of the emitted photon pairs and enlarges the intensity difference between two cavity modes, which leads to the striking asymmetry in the mean photon numbers and then induces the unidirectional steerability from the mode generated by the upper transition to the mode in the low transition. The present scheme may provide a resource in a long-distance quantum network for quantum secret sharing protocol.

Correlated Emission Laser and Quenching of Spontaneous Emission

Correlated Emission Laser and Quenching of Spontaneous Emission

OUTPUT ENTANGLEMENT IN A FOUR-LEVEL CORRELATED EMISSION LASER

The continuous-variable (CV) entanglement of the output fields is investigated in a four-level correlated emission laser system. The atomic coherence is introduced using two external classical driving fields. Based on the input–output theory, it is shown that the output entanglement and the entangled photons of the system can be achievable under certain conditions. Moreover, it is found that the two-mode entanglement has a close relation with the intensities of two external driving fields.

Entanglement of movable mirrors in a correlated emission laser via cascade-driven coherence

Entanglement of movable mirrors in a correlated emission laser via cascade-driven coherence

Entanglement of movable mirrors in a correlated-emission laser

We propose an experimental scheme for entangling two macroscopic mechanical resonators (movable mirrors) by their coupling to the two-mode fields of a correlated-emission laser inside a doubly resonant cavity. With this aim we investigate the quantum Langevin equations that describe the interaction of the field-mirror system in conjuction with the master equation of the correlated-emission laser. We show that the steady-state entanglement of two mirrors as well as that of two-mode fields can be obtained in the regime of strong field-mirror coupling when the input lasers are scattered at the anti-Stokes sidebands. Remarkably, the degree of entanglement for both the mirror pair and the field pair can be controlled by an external field driving the gain medium. Our scheme is able to entangle two macroscopic objects with current state-of-the-art experimental apparatus.

Continuous variable quantum discord in a correlated emission laser

A detailed analysis of the nonclassical features of the cavity radiation of a nondegenerate correlated emission laser is presented. Closed mathematical relation that describes the quantum discord in terms of the involved auto- and cross-correlations is provided. It is found that the quantum discord increases with the linear gain coefficient and initially prepared atomic coherent superposition. Although the overall trend of the forward and backward quantum discords turns out to be similar, it is also unequivocally observed that the forward quantum discord is greater or equal to the backward quantum discord. Moreover, comparison of the quantum discord with entanglement shows that there is a very wide range of parameters for which an overlap in capturing the nonclassical nature of the radiation can be observed. However, when the atoms are initially prepared in a maximum coherent superposition, the quantum discord is found to capture the quantumness even when Duan–Giedke–Cirac–Zoller entanglement criterion failed.

Effect of phase fluctuation and dephasing on the dynamics of entanglement generation in a correlated emission laser

A detailed study of the effects of phase fluctuation and dephasing on the dynamics of the entanglement generated from a coherently pumped correlated emission laser is presented. It is found that the time evolution of the entanglement significantly depends on the phase fluctuation and dephasing, particularly, at early stages of the lasing process. In the absence of the external driving radiation, the degree of entanglement turns out to attain a maximum value just before starting to exhibit oscillation that dies at a longer time scale. However, in case the driving mechanism is on, the oscillatory nature disappears due to the additional induced coherent superposition and the degree of entanglement can be larger at steady state. Moreover, the degree of entanglement as predicted by the logarithmic negativity and the Duan-Giedke-Cirac-Zoller criteria exhibits a similar nature when there is no driving radiation, although such a trend is eroded with increasing strength of the pumping radiation at a longer time scale. It is also observed that the phase fluctuation and dephasing can increase the time at which the maximum entanglement is detected.

Dynamics of the cavity radiation of a correlated emission laser initially seeded with a thermal light

A detailed analysis of the time evolution of the two-mode squeezing, entanglement and intensity of the cavity radiation of a two-photon correlated emission laser initially seeded with a thermal light is presented. The dependences of the degree of two-mode squeezing and entanglement on the intensity of the thermal light and time are found to have a more or less similar nature, although the actual values differ, especially in the early stages of the process and when the atoms are initially prepared with nearly 50:50 probability to be in the upper and lower energy levels. Seeding the cavity degrades the nonclassical features significantly, particularly in the vicinity of t=0. It is also shown that the mean photon number in a wider time span has a dip when mode b is seeded but a peak when mode a is seeded. Moreover, it turns out that the effect of the seed light on the nonclassical features and intensity of the cavity radiation decreases significantly with time, an outcome essentially attributed to the pertinent emission–absorption mechanism. This can be taken as an encouraging aspect in the practical utilization of this model as a source of a bright entangled light.

Coherently prepared nondegenerate Y-shaped four-level correlated emission laser: A source of tripartite entangled light

A detailed derivation of the master equation of the cavity radiation of a coherently prepared $Y$-shaped four-level correlated emission laser is presented. The outline of the procedures that can be employed in analytically solving the stochastic differential equations and the rate equations of various correlations are also provided. It is shown that coherently preparing the atoms in the upper two energy levels and the lower, initially, can lead to a genuine continuous variable tripartite entanglement. Moreover, preparing the atoms in the coherent superposition, other than the possible maximum or minimum, of the upper two energy levels, leaving the lower unpopulated, may lead to a similar observation. With the possibility of the atom at the intermediate energy level to take three different transition roots guided by the induced coherence, this system in general is found to encompass versatile options for practical utilization. In particular, coupling at least one of the dipole forbidden transitions by an external radiation is expected to enhance the degree of detectable entanglement.

Dependence of the evolution of the cavity radiation of a coherently pumped correlated emission laser on dephasing and phase fluctuation

Analysis of the dynamics of the cavity radiation of a coherently pumped correlated emission laser is presented. The phase fluctuation and dephasing are found to affect the time evolution of the two-mode squeezing and intensity of the cavity radiation significantly. The intensity and degree of the two-mode squeezing increase at early stages of the process with time, but this trend changes rapidly afterwards. It is also shown that they increase with phase fluctuation and dephasing in the strong driving limit, however the situation appears to be opposite in the weak driving limit. This essentially suggests that the phase fluctuation and dephasing weaken the coherence induced by a strong driving mechanism so that the spontaneous emission gets a chance. The other important aspect of the phase fluctuation, in this regard, is the relaxation of the time at which the maximum squeezing is manifested as well as the time in which the radiation remains in a squeezed state.