Showing papers on "Atomic coherence published in 2021"

Quantum Entanglement and Modulation Enhancement of Free-Electron-Bound-Electron Interaction.

Abstract: The modulation and engineering of the free-electron wave function bring new ingredients to the electron-matter interaction. We consider the dynamics of a free-electron passing by a two-level system fully quantum mechanically and study the enhancement of interaction from the modulation of the free-electron wave function. In the presence of resonant modulation of the free-electron wave function, we show that the electron energy loss and gain spectrum is greatly enhanced for a coherent initial state of the two-level system. Thus, a modulated electron can function as a probe of the atomic coherence. We further find that distantly separated two-level atoms can be entangled through interacting with the same free electron. Effects of modulation-induced enhancement can also be observed using a dilute beam of modulated electrons.

Atomic population inversion and absorption dispersion-spectra driven by modified double-exponential quotient pulses in a three-level atom

Abstract: 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.

Superradiant lasing in inhomogeneously broadened ensembles with spatially varying coupling

Abstract: Theoretical studies of superradiant lasing on optical clock transitions predict a superb frequency accuracy and precision closely tied to the bare atomic linewidth. Such a superradiant laser is also robust against cavity fluctuations when the spectral width of the lasing mode is much larger than that of the atomic medium. Recent predictions suggest that this unique feature persists even for a hot and thus strongly broadened ensemble, provided the effective atom number is large enough. Here we use a second-order cumulant expansion approach to study the power, linewidth and lineshifts of such a superradiant laser as a function of the inhomogeneous width of the ensemble including variations of the spatial atom-field coupling within the resonator. We present conditions on the atom numbers, the pump and coupling strengths required to reach the buildup of collective atomic coherence as well as scaling and limitations for the achievable laser linewidth.

Four-wave mixing in a ladder configuration of warm 87Rb atoms: a theoretical study.

Abstract: We present a theoretical study of the four-wave mixing (FWM) spectra of 5S1/2 − 5P3/2 − 5D5/2 ladder-type transitions of 87Rb atoms. The density matrix equations are solved by considering all the magnetic sublevels to calculate the FWM signals in the atomic vapor cell. These results are subsequently compared with the experimental results. We observe that the FWM signal propagating exactly opposite to the driving field is measured experimentally. Additionally, we demonstrate the effects of optical depth, laser linewidths, and the coupling field power on the FWM spectra. Finally, the origin of the dispersive-like FWM signal is investigated by intentionally varying the intrinsic atomic properties.

Nonclassical atomic system dynamics time-dependently interacts with finite entangled pair coherent parametric converter cavity fields

Abstract: We consider a time-dependent model that describes a qubit time-dependently interacting with a cavity containing finite entangled pair coherent parametric converter fields. The dynamics of some quantum phenomena, as: phase space information, quantum entanglement and squeezing, are explored by atomic Husimi function, atomic Wehrl entropy, variance, and entropy squeezing. The influences of the unitary qubit-cavity interaction, the difference between the two-mode photon numbers, the initial atomic coherence, and the time-dependent qubit location are investigated. It is found that the regularity, the amplitudes and the frequency of the quantum phenomena can be controlled by the physical parameters. For the initial atomic pure state, the qubit-cavity entanglement, the qubit phase space information, and atomic squeezing can be generated strongly compared to those of the initial atomic mixed state. The time-dependent location parameters enhance the generated quantum phenomena, and their effect can be enhanced by the parameters of the two-mode photon numbers and the initial atomic coherence.

Experimental Observation of Partial Parity-Time Symmetry and Its Phase Transition with a Laser-Driven Cesium Atomic Gas

Abstract: Realization and manipulation of parity-time (PT) symmetry in multidimensional systems are highly desirable for exploring nontrivial physics and uncovering exotic phenomena in non-Hermitian systems. Here, we report the first experimental observation of partial PT (pPT) symmetry in a cesium atomic gas coupled with laser fields, where a two-dimensional pPT-symmetric optical potential for probe laser beam is created. A transition of the pPT symmetry from an unbroken phase to a broken one is observed through changing the beam-waist ratio of the control and probe laser beams, and the domains of unbroken, broken, and non-pPT phases are also discriminated unambiguously. Moreover, we develop a technique to precisely determine the location of the exceptional point of the pPT symmetry breaking by measuring the asymmetry degree of the probe-beam intensity distribution. The findings reported here pave the way for controlling multidimensional laser beams in non-Hermitian systems via laser-induced atomic coherence, and have potential applications for designing new types of light amplifiers and attenuators

Quantum properties of correlated emission laser with dephasing and phase fluctuation

Abstract: 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.

The Role of Phase-Dependent Atomic Coherence on Refractive Index of Atomic Medium for Energy Harvesting Systems

Abstract: Quantum enhancement of the optical behavior for V −type open atomic system is examined analytically. With consideration of the system which contain N number of atoms, it is derived that the evolution of the atomic variable evolution with respect to time. At steady state, the optical properties of the system have been analyzed. The phase between the upper doublet levels is influencing the optical parameters change in the system. It is observed that for small values of the phase between the upper doublet energy states, the better refractive index of the atomic medium. The refractive index gets the peak value near to the resonance frequency of the probe field. The properties of the re-emitted light from ensemble of three-level atoms have been analyzed in details. In this regard, it is observed that the height of the power spectrum increased while the number of atoms are large in the sample.

Strongly-Entangled Twin Beams Produced by a Coherent Beat Laser Coupled to Thermal Reservoir

Abstract: Applying the combination of the master and stochastic differential equations, we investigate in detail a continuous-variable entanglement of the twin beam generated by the coherent beat laser containing a parametric amplifier and coupled to thermal light of an external environment. The dipole-forbidden transition of the three-level atoms are coupled by the initial coherent superposition and classical pumping light emerging from the parametric oscillator. The atomic coherence induced by the classical pumping field and the initial coherent superposition induce a strong correlation between the two-mode radiation, which results in a high degree of the photon entanglement. In addition, the parametric amplifier enhances the achievable degree of entanglement of the two-mode fields. On the other hand, thermal light appears to degrade entanglement but a strong photon entanglement can be generated by managing the amount of thermal noise entering into the laser cavity through the output mirror.

Transport of light in a moving photonic lattice via atomic coherence.

Abstract: In this Letter, we have investigated experimentally the photonic realization of a moving lattice with an instantaneously tunable transverse velocity in a three-level Λ-type warm 85Rb atomic medium. The dynamic photonic lattice moving along the direction of its spatial periodicity was constructed by introducing a frequency difference (determining the velocity) between two coupling beams, whose interference pattern could optically induce a (spatial) periodic refractive index change inside the atomic vapor under electromagnetically induced transparency. When a Gaussian probe field is launched into this optically induced lattice, the output diffraction patterns can shift along the transverse direction, indicating dynamical features of induced photonic structures. The realization of this effectively controllable moving photonic lattice provides a new platform for guiding the transport of light.

Quantum enhancement of the optical behavior for V−type open atomic system

Abstract: In this paper, the non-classical modification of optical behavior for V−type open atomic system is analyzed analytically. With consideration of the system contains N number of atoms, it is obtained that the evolution of the atomic variable with respect to time. At steady state, the optical natures of the system have been discussed. It is observed that the phase between the upper doublet levels is influencing the optical parameters of the system. It is also obtained that for small values of the phase angle between the upper doublet energy states, it is possible to attain better refractive index of the atomic medium. The refractive index gets the peak value near to the resonance frequency of the probe field. The properties of the re-emitted light from ensemble of three-level atoms have been also analyzed in details. In this regard, it is observed that the height of the power spectrum increased while the number of atoms are large in the sample.

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

Abstract: 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.

Laser interferometry based on atomic coherence

Abstract: We demonstrate laser interferometry based on phase difference between the two arms of an interferometer. The experiments are done with a Cs atomic vapor cell at room temperature and use atomic coherence. The interference can be tuned from constructive to destructive by tuning the relative phase between the two arms. It is similar to the Michelson interferometer, but differs in the important aspect of allowing interference when the polarizations in the two arms are orthogonal. This would be a novel method for interfering two independent lasers, which can even allow interfering two independent lasers of completely different wavelengths. © 2021 Institute of Physics Publishing. All rights reserved.

Testing quantum gravity with interactive information sensing

Abstract: We suggest a test of a central prediction of perturbatively quantized general relativity: the coherent communication of quantum information between massive objects through gravity. To do this, we introduce the concept of interactive quantum information sensing, a protocol tailored to the verification of dynamical entanglement generation between a pair of systems. Concretely, we propose to monitor the periodic wavefunction collapse and revival in an atomic interferometer which is gravitationally coupled to a mechanical oscillator. We prove a theorem which shows that, under the assumption of time-translation invariance, this collapse and revival is possible if and only if the gravitational interaction forms an entangling channel. Remarkably, as this approach improves at moderate temperatures and relies primarily upon atomic coherence, our numerical estimates indicate feasibility with current devices.

The different behaviors of thermal noise in collective quantum steering and genuinely tripartite steering induced by atomic coherence

Abstract: Multipartite quantum steering has important application in quantum information processing. Here we study the influence of thermal noise on the collective quantum steering and genuine tripartite steering in a system of four-level inverted Y-type atoms, in which the atomic coherence is initially prepared and the cavity is coupled to a thermal reservoir. It is found that for the cases of the balanced and unbalanced cavity losses, the thermal noise plays a positive role in realizing the collective steering. However the case is different for the genuine tripartite steering effect. For the case of either balanced or unbalanced cavity losses, the thermal noise would destroy genuine tripartite steering effect and reduce the parameter region of genuine tripartite steering. The thermal noise plays a negative role in realizing genuine tripartite steering. Specially, it is verified that the genuine tripartite steering does not reject the bipartite steering, which is very different from the collective quantum steering requiring no bipartite steering. The present scheme may provide some help for potential applications such as quantum communication.

Few-cycle excitation of atomic coherence: A closed-form analytical solution beyond the rotating-wave approximation

Abstract: Developing an analytical theory for atomic coherence driven by ultrashort laster pulses has proved to be challenging due to the breakdown of the rotating wave approximation (RWA). In this paper, we present an approximate, closed-form solution to the Schrodinger equation that describes a two-level atom under the excitation of a far-off-resonance, few-cycle pulse of arbitrary shape without invoking the RWA. As an example of its applicability, an analytical solution for Gaussian pulses is explicitly given. Comparisons with numerical solutions validate the accuracy our solution within the scope of the approximation. Finally, we outline an alternative approach that can lead to a more accurate solution by capturing the nonlinear behaviors of the system.

Atomic magnetometer system

Abstract: An atomic magnetometer system is disclosed that includes a variable magnetic field source (14) configured to provide an oscillating primary magnetic field to cause a sample (16) to produce a secondary magnetic field. The atomic magnetometer system also includes an atomic magnetometer for detecting the secondary magnetic field. The atomic magnetometer includes an atomic specimen, a pump and probe subsystem configured to pump the atomic specimen to create a polarisation and to probe atomic coherence precession within the atomic specimen with a probe beam, a detector configured to detect the probe beam to produce a detection signal. The system is configured to drive the variable magnetic field source (14) in dependence on the detection signal with a frequency tuned to rf resonance. A method of operating an atomic magnetometer is also disclosed.

Attosecond optical and Ramsey-type interference

Abstract: Molecular or atomic coherence generated with the irradiation of ultrashort optical pulses should make a significant role for realizing the control of quantum states in a matter. By virtue of the advancement of the ultrashort light sources towards the short wavelength region, the energy range of the quantum states that could be coherently generated reached much more than 15 eV at the present [1] . In particular, Ramsey-type interference fringes observed by scanning the delay between a pair of phase-locked XUV femtosecond pulses unveiled spectral information of the atomic states [2] - [4] . The time ranges of the delay scans in such preceding studies were long enough to finely resolve the spectral features, while the XUV pulse pairs could not temporally overlap because the light sources were split into two before generating the XUV pulses. The near 0 delay control of the XUV pulse pair is important for investigating the dynamics of a cationic system entangled with an ionized continuum electron [5] . In this paper, we performed the delay scan of the XUV pulse pair starting from the complete temporal overlap to show that the optical interference seamlessly continued to the Ramsey-type atomic interference as a prototype of such study.

Quantum interference between photons and single quanta of stored atomic coherence

Abstract: Quantum networks largely rely on beamsplitters to linearly mix identical photons from independent sources. The essential indistinguishability of these source photons is revealed by their bunching and the associated coincidence dip in the Hong-Ou-Mandel interferometer. However, indistinguishability is not limited only to the same type of bosons. For the first time, we hereby observe in an atom-light beamsplitter interface, quantum interference between flying photons and a single quantum of stored atomic coherence (magnon), which can be transformed reversibly to a single photon for use in quantum memories. We demonstrate experimentally that the Hermiticity of this interface determines the type of quantum interference between photons and atoms. Not only bunching that characterizes bosons is observed, but, counterintuitively, fermion-like antibunching as well. The hybrid nature of the demonstrated magnon-photon quantum interface can be applied to versatile memory platforms and leads to controllable photon distribution in linear network which is fundamentally different from boson sampling.

Superradiant lasing in inhomogeneously broadened ensembles with spatially varying coupling

Abstract: Background : Theoretical studies of superradiant lasing on optical clock transitions predict a superb frequency accuracy and precision closely tied to the bare atomic linewidth. Such a superradiant laser is also robust against cavity fluctuations when the spectral width of the lasing mode is much larger than that of the atomic medium. Recent predictions suggest that this unique feature persists even for a hot and thus strongly broadened ensemble, provided the effective atom number is large enough. Methods : Here we use a second-order cumulant expansion approach to study the power, linewidth and lineshifts of such a superradiant laser as a function of the inhomogeneous width of the ensemble including variations of the spatial atom-field coupling within the resonator. Results : We present conditions on the atom numbers, the pump and coupling strengths required to reach the buildup of collective atomic coherence as well as scaling and limitations for the achievable laser linewidth. Conclusions : We show how sufficiently large numbers of atoms subject to strong optical pumping can induce synchronization of the atomic dipoles over a large bandwidth. This generates collective stimulated emission of light into the cavity mode leading to narrow-band laser emission at the average of the atomic frequency distribution. The linewidth is orders of magnitudes smaller than that of the cavity as well as the inhomogeneous gain broadening and exhibits reduced sensitivity to cavity frequency noise.