Coherent Optical Fields Research Articles

Isoentropic partially coherent optical fields that cannot be interconverted unitarily

Isoentropic partially coherent optical fields that cannot be interconverted unitarily

Twisted spatiotemporal optical vortex beams in dispersive media

We derive a closed-form expression for the mutual coherence function (MCF) of a twisted spatiotemporal optical vortex (STOV) beam after propagating a distance z in a linear dispersive medium. A twisted STOV beam is a partially coherent optical field that possesses a coherent STOV and a stochastic twist coupling its space and time dimensions. These beams belong to a special class of space–time-coupled light fields that carry transverse (to the direction of propagation) orbital angular momentum, making them potentially useful in numerous applications including quantum optics, optical manipulation, and optical communications. After presenting the derivation, we validate our new general MCF by showing that it simplifies to the MCFs for two example beams from the literature. Lastly, we present and analyze space–time beam profiles and complex arguments (phases) of the MCF at multiple z and differing amounts of material dispersion, field correlation or coherence, and beam twist to gain insight into how twisted STOV beams evolve in dispersive media. We conclude with a brief summary.

OPTICAL SPECKLE-FIELD VISIBILITY DIMINISHING BY REDUCTION OF A TEMPORAL COHERENCE

The paper is a report of an experimental study to suppress the speckle structure of a coherent optical field. The technique proposed is based on the reduction of the temporal coherence utilizing enriching the output spectrum of Nd:YVO4 laser with intra-cavity second harmonic generation by additional emission lines. Temperature-controlled simultaneous emission of two components at 1.063 mm and 1.066 mm with nearly equal intensities in IR is achived. In the second-harmonic output the emission lines 531.7 nm, 532.3 nm and 532.8 nm were recorded. The influence of the spectrum variation on the formation of a speckle field was checked. Successfully removed intensity zeros and reduced contrast (visibility) from 0.92 to 0.65 in a light scattered by a ground glass diffuser at the angle 35°. A simple consideration of the speckle field dumping mechanism is presented.

Macroscopic quantum entanglement between an optomechanical cavity and a continuous field in presence of non-Markovian noise

Probing quantum entanglement with macroscopic objects allows us to test quantum mechanics in new regimes. One way to realize such behavior is to couple a macroscopic mechanical oscillator to a continuous light field via radiation pressure. In view of this, the system that is discussed comprises an optomechanical cavity driven by a coherent optical field in the unresolved sideband regime where we assume Gaussian states and dynamics. We develop a framework to quantify the amount of entanglement in the system numerically. Different from previous work, we treat non-Markovian noise and take into account both the continuous optical field and the cavity mode. We apply our framework to the case of the Advanced Laser Interferometer Gravitational-Wave Observatory and discuss the parameter regimes where entanglement exists, even in the presence of quantum and classical noises. Published by the American Physical Society 2024

Locked entropy in partially coherent optical fields

Locked entropy in partially coherent optical fields

Single-Photon Level Dispersive Fourier Transform: Ultrasensitive Characterization of Noise-Driven Nonlinear Dynamics.

Dispersive Fourier transform is a characterization technique that allows directly extracting an optical spectrum from a time domain signal, thus providing access to real-time characterization of the signal spectrum. However, these techniques suffer from sensitivity and dynamic range limitations, hampering their use for special applications in, e.g., high-contrast characterizations and sensing. Here, we report on a novel approach to dispersive Fourier transform-based characterization using single-photon detectors. In particular, we experimentally develop this approach by leveraging mutual information analysis for signal processing and hold a performance comparison with standard dispersive Fourier transform detection and statistical tools. We apply the comparison to the analysis of noise-driven nonlinear dynamics arising from well-known modulation instability processes. We demonstrate that with this dispersive Fourier transform approach, mutual information metrics allow for successfully gaining insight into the fluctuations associated with modulation instability-induced spectral broadening, providing qualitatively similar signatures compared to ultrafast photodetector-based dispersive Fourier transform but with improved signal quality and spectral resolution (down to 53 pm). The technique presents an intrinsically unlimited dynamic range and is extremely sensitive, with a sensitivity reaching below the femtowatt (typically 4 orders of magnitude better than ultrafast dispersive Fourier transform detection). We show that this method can not only be implemented to gain insight into noise-driven (spontaneous) frequency conversion processes but also be leveraged to characterize incoherent dynamics seeded by weak coherent optical fields.

Efficient two-dimensional Fraunhofer diffraction pattern via electron spin coherence

In this letter, we have discussed the two-dimensional diffraction pattern via electron spin coherence in a GaAs quantum dot. Impulsive stimulated Raman excitation utilizing coherent optical fields is employed for the purpose of regulating the electron spin coherence within a charged ensemble of GaAs quantum dots, by means of an intermediate charged exciton (trion) state. We show that for the coupling two-dimensional standing wave (SW) field in the x and y directions, the two-dimensional Fraunhofer pattern can be formed for a weak probe light. By using the experimental parameters and controlling the Rabi frequency of the SW field and relative phase between applied lights, the symmetry and asymmetry diffraction pattern are obtained for the weak probe light due to the four-wave mixing mechanism. Our proposed model may have potential applications in high-capacity optical communications and quantum information technologies.

Analysis of laser-induced transient population gratings by different types of exciting pulse

Motivated by atomic response to different initial coherent optical fields, we comparatively studied transient population grating (TPG) induced by successive pulse train. Time delay and pump pulse duration dependence of TPG is achieved by numerically solving the density matrix equations. Results reveal that the creation and erasure of TPG is possible by choosing the appropriate pulse parameters, which is illustrated by Bloch sphere model and quantitative validation. To obtain desired large grating amplitude for rectangular pulse, the allowed pulse duration can be extended to one order wider than that of Gaussian pulse. Population grating can be erased to near zero by a third pulse with time delay by an odd multiple of half the pulse width, and it also can be erased further to recover atom assembly back to the initial state by a fourth pulse with time delay equal to an integer multiple of pulse width. Atomic behaviors excited by different types of pulse presented here may be significant to manipulate TPG during coherent light-matter interaction.

Acousto-optical camera for super-resolution imaging

I will present a hybrid acousto-optical imaging system that probes the environment with acoustic waves, converts the back-scattered sound into a coherent optical field on an aperture using an acousto-optical metasurface, and focuses the latter into an image with existing optical lenses. Preliminary theoretical analysis and experiments show that this approach can produce images of significantly higher resolution than possible with conventional methods, thus enabling high quality images produced with low frequency probing sound. Our imaging approach takes advantage of the best properties of optic and acoustic waves, namely, (1) the high image quality produced by existing optical systems and (2) the ability of low frequency acoustic waves to penetrate most materials. An additional advantage of our method is that it puts essentially no constraints on the sound source. For example, the source could have low directivity and may consist of a single transducer or it could even miss when imaging noisy environments. In the latter scenarios, our imaging method becomes purely passive.

Optical bistability and multistability via electron injection rate in an imperfect cavity

In this letter, we investigate the electron injection rate-based optical bistability (OB) and optical multistability (OM) features in an imperfect cavity. Coherent optical fields interact with the open four-level quantum system that makes up the ring cavity. We have discovered that the threshold of OB and OM as well as the length of the hysteresis loop can be changed by varying the length of the quantum system, reflection and transmission coefficient of cavity mirrors. Our findings further show that the electronic exit rate from the cavity and the electron injection rates have a significant impact on the threshold of OB and OM. It is discovered that transitioning from OB to OM or vice versa is achievable by adjusting the controllable parameters. The impact of the cooperation parameter on the properties of the OB and OM is then addressed. The findings demonstrate that the OB features are simple to manipulate. Our suggested model might be used to develop an all-optical device for use in upcoming quantum information processing.

Large-bandwidth Transduction Between an Optical Single Quantum Dot Molecule and a Superconducting Resonator

Quantum transduction between the microwave and optical domains is an outstanding challenge for long-distance quantum networks based on superconducting qubits. For all transducers realized to date, the generally weak light-matter coupling does not allow high transduction efficiency, large bandwidth, and low noise simultaneously. Here we show that a large electric dipole moment of an exciton in an optically active self-assembled quantum dot molecule (QDM) efficiently couples to a microwave resonator field at a single-photon level. This allows for transduction between microwave and optical photons without coherent optical pump fields to enhance the interaction. With an on-chip device, we demonstrate a sizeable single-photon coupling strength of 16 MHz. Thanks to the fast exciton decay rate in the QDM, the transduction bandwidth between an optical and microwave resonator photon reaches several 100s of MHz.

Optical computing of quantum revivals.

Interference is the mechanism through which waves can be structured into the most fascinating patterns. While for sensing, imaging, trapping, or in fundamental investigations, structured waves play nowadays an important role and are becoming the subject of many interesting studies. Using a coherent optical field as a probe, we show how to structure light into distributions presenting collapse and revival structures in its wavefront. These distributions are obtained from the Fourier spectrum of an arrangement of aperiodic diffracting structures. Interestingly, the resulting interference may present quasiperiodic structures of diffraction peaks on a number of distance scales, even though the diffracting structure is not periodic. We establish an analogy with revival phenomena in the evolution of quantum mechanical systems and illustrate this computation numerically and experimentally, obtaining excellent agreement with the proposed theory.

Quantum treatment of cavity-assisted entanglement of three-level atoms and two fields in an electromagnetically-induced-transparency configuration

We examine the field-field and field-atom entanglements generated by \ensuremath{\Lambda}-type three-level atoms placed in an optical cavity driven above threshold by two coherent input optical fields. It is shown that under realistic experimental conditions entanglement between the two output cavity fields as well as between the fields and the atoms can be achieved when the two cavity fields are both one- and two-photon (Raman) resonant with the atomic transitions, as in the configuration for electromagnetically induced transparency (EIT). The entanglement has similar features to pump-signal-idler three-color entanglement in an above-threshold optical parametric oscillator [Villar et al., Phys. Rev. Lett. 97, 140504 (2006)]. This cavity-enhanced atom-field cooperative coupling could enable convenient and efficient generation of bright, nondegenerate, narrow-band entangled fields, which may find potential applications in realistic quantum communications and networking protocols.

Special correlation model sources producing a self-focusing field.

We evaluate the modes for non-Schell-model sources whose degrees of spectral coherence depend on the difference of the special function values of the position coordinated of two points. It is shown that such sources modulated by various function possess different spatial coherence properties, and cause them to produce the self-focusing fields with different characteristics. The results suggest a convenient method for modeling novel classes of partially coherent self-focusing optical fields.

Numerical studies of the saturated absorption resonances in a nonlinear spectroscopy of the degenerate atomic transitions

The physical processes forming the saturated absorption resonance spectra at a number of degenerate atomic transitions at their interaction with coherent optical fields and incoherent ield of spontaneous radiation of excited atoms are studied numerically. The features of behavior of nonlinear resonance spectra depending on the degree of degeneration and relaxation parametersof level transitions, character of polarizations and intensities, as well as direction of propagation of optical fields are analyzed.

Unitary learning for diffractive deep neural network

Realization of deep learning with coherent diffraction has achieved remarkable development nowadays, which benefits on the fact that matrix multiplication can be optically executed in parallel with high band-with and low latency. Coherent optical field in the form of complex-valued entity can be manipulated into a task-oriented output. In this paper, a modulation mechanism is established by implementing the equivalence between a digital deep unitary neural network and optical coherent diffraction. We present a unitary learning avenue on diffractive deep neural network, meeting the physical unitary prior in coherent diffraction. The Unitary learning is a Backpropagation serving to unitary weights update through the gradient translation from Euclidean to Riemannian space. The temporal-space evolution characteristics in unitary learning are formulated and elucidated. And a compatible condition on how to select the nonlinear activation in complex space is unveiled, encapsulating the fundamental sigmoid, tanh and quasi-ReLu in complex space available in a single channel training. The performance of phase-ReLu is particularly emphasized. As a preliminary application, diffractive deep neural network with unitary learning is tentatively implemented on the 2D classification and verification tasks.

Photoacoustic detection of low duty cycle gratings through optically opaque layers

We report on the use of ultra-high frequency photoacoustics to detect gratings with linewidths as narrow as 75 nm, buried underneath optically opaque metal layers. Our results show that buried gratings can be detected by observing diffraction from the spatially periodic acoustic replica of the buried grating at the glass/metal interface and from replicas of the acoustic wave inside the glass substrate. The measured diffraction signals show a linear dependence on grating duty cycle rather than the expected quadratic one. We find that this is due to the presence of a coherent background optical field, which interferes with and coherently amplifies the weaker fields diffracted off the grating-shaped acoustic waves. Our measurements show that ultra-high frequency photoacoustics is a promising technique for detection of sub-wavelength periodic nanostructures.

Optical lock-in camera for gravitational wave detectors.

Knowledge of the intensity and phase profiles of spectral components in a coherent optical field is critical for a wide range of high-precision optical applications. One of these is interferometric gravitational wave detectors, which rely on the optical beats between these fields for precise control of the experiment. Here we describe an optical lock-in camera and show that it can be used to record optical beats at MHz or greater frequencies with higher spatial and temporal resolution than previously possible. This improvement is achieved using a Pockels cell as a fast optical switch to transform each pixel on a sCMOS array into an optical lock-in amplifier. We demonstrate that the optical lock-in camera can record fields with 2 Mpx resolution at 10 Hz with a sensitivity of -62 dBc when averaged over 2s.

Statistical Aspects and Dynamical Entanglement for a Two-Level Atom Moving on Along Cavity Length of x-Direction: Atomic Position Distribution

In this work, the problem of the quantum optical model is considered where an one-mode quantized radiation field interacts with a two-level atom (TLA). Also, the atomic position distribution is taken into account, i.e., the atom passing through the length of the optical cavity. We believe that the atomic position affects the matter-field interaction and can be realized in several multiple experiments, such as ultracold atoms and trapped ions. We take into consideration the atom is moving along the cavity field in the x-direction so that the time-position Schrodinger equation for the atom in the x-direction is obtained. We suppose that the field is initially prepared in a coherent state optical field and the atom is initially prepared in an excited state. Also, the atomic motion along the cavity length vanishes in the cavity wall. By using the Laplace transformation method, an exact analytical solution for the coupled partial differential Schrodinger equation for the wave function is calculated. Some non-classical statistical aspects such as the atomic inversion and the photon distributions are discussed in detail. The collapses-revivals, the Poissonian distributions of the photon by Mandel Q parameter, the degrees of the entanglement, and the fidelity have been investigated. The effect of the atomic position distribution in the x-direction on these phenomena is examined. We observed that the atomic position distribution along the cavity has an effective effect on the quantum statistical properties of these phenomena. Minutely, the influence of the atom location distribution on the amount of quantum entanglement has been obtained.

Full Counting Statistics of Electrons through Interaction of the Single Quantum Dot System with the Optical Field.

In this paper, using the particle-number-resolved master equation, the properties of full counting statistics (FCS) are investigated for a single quantum dot (QD) system interacting with optical fields in the thermal state, Fock state, coherent state, and coherent state with random phase. In these diverse quantum states of optical fields, average tunneling currents have different step shoulder heights at a lower bias voltage with the same light intensity, and a staircase-shaped current can be induced unexpectedly in vacuum state optical field. The characteristics of the Fano factor and skewness in the coherent state differ from those in all of the other cases. For avalanche-like transport at a lower bias voltage, the mechanism is a dynamical channel blockade in a moderate electron–photon interaction regime. There is a pronounced negative differential conductance that results from tuning the phase of the coherent state optical field in a symmetric QD system.