High-gain Regime Research Articles

Limitations in fluorescence-detected entangled two-photon-absorption experiments: Exploring the low- to high-gain squeezing regimes

Limitations in fluorescence-detected entangled two-photon-absorption experiments: Exploring the low- to high-gain squeezing regimes

Generating superposition of squeezed states and photon-added squeezed states

The scheme of an arrangement is considered for the preparation of some non-classical superposed states from squeezed states by using the optical parametric amplifier (OPA) apparatus, which is based on an idea recently proposed to generate photon-added states from the coherent states of light. This technique allows one to obtain linear combinations of squeezed vacuum states (SVSs) and n-photon-added squeezed vacuum states (n-PASVSs), that can enrich the non-classicality of the SVSs and n-PASVSs and improve their performances in quantum information protocols. Their characteristics are greatly affected by the gain of the OPA and the coherent field amplitude (or, mean number of photons). For this purpose, a comprehensive analysis of the non-classical features of these states has been presented in four different behavioral regimes, i.e. low- and high-gain regimes in the presence of weak and strong coherent fields. Finally, the role of the gain parameter of the light state from OPA as one of the input states of the Mach–Zehnder interferometer (MZI) apparatus in phase sensitivity optimization is discussed.

Quantum imaging beyond the standard-quantum limit and phase distillation

Quantum sensing using non-linear interferometers (NLIs) offers the possibility of bicolour imaging, using light that never interacted with the object of interest, and provides a way to achieve phase supersensitivity, i.e. a Heisenberg-type scaling of the phase uncertainty. Such a scaling behaviour is extremely susceptible to noise and only arises at specific phases that define the optimal working point (WP) of the device. While phase-shifting algorithms are to some degree robust against the deleterious effects induced by noise they extract an image by tuning the interferometer phase over a broad range, implying an operation beyond the WP. In our theoretical study, we investigate both the spontaneous and the high-gain regime of operation of an NLI. In fact, in the spontaneous regime using a distillation technique and operating at the WP leads to a qualitatively similar behaviour. In the high-gain regime, however, typical distillation techniques inherently forbid a scaling better than the standard-quantum limit, as a consequence of the photon statistics of squeezed vacuum. In contrast, an operation at the WP still may lead to a sensitivity below shot noise, even in the presence of noise. Therefore, this procedure opens the perspective of bicolour imaging with a better than shot-noise phase uncertainty by working in the vicinity of the WP. Our results transfer quantum imaging distillation in a noisy environment to the high-gain regime with the ultimate goal of harnessing its full potential by combining bicolour imaging and phase supersensitivity.

Frequency-domain engineering of bright squeezed vacuum for continuous-variable quantum information.

Multimode bright squeezed vacuum is a non-classical state of light hosting a macroscopic photon number while offering promising capacity for encoding quantum information in its spectral degree of freedom. Here, we employ an accurate model for parametric down-conversion in the high-gain regime and use nonlinear holography to design quantum correlations of bright squeezed vacuum in the frequency domain. We propose the design of quantum correlations over two-dimensional lattice geometries that are all-optically controlled, paving the way toward continuous-variable cluster state generation on an ultrafast timescale. Specifically, we investigate the generation of a square cluster state in the frequency domain and calculate its covariance matrix and the quantum nullifier uncertainties, that exhibit squeezing below the vacuum noise level.

Theory of two-photon absorption with broadband squeezed vacuum

We present an analytical quantum theoretic model for nonresonant molecular two-photon absorption (TPA) of broadband, spectrally multimode squeezed vacuum, including low-gain (isolated entangled photon pairs) and high-gain (bright squeezed vacuum or BSV) regimes. The results are relevant to the potential use of entangled-light TPA as a spectroscopic and imaging method. We treat the scenario that the exciting light is spatially single mode and is nonresonant with all intermediate molecular states. In the case of high gain, we find that in the case that the linewidth of the final molecular state is much narrower than the bandwidth of the exciting light, bright squeezed vacuum is found to be equally (but no more) effective in driving TPA as is a quasimonochromatic coherent-state (classical) pulse of the same temporal shape, duration, and mean photon number. Therefore, in this case the sought-for advantage of observing TPA at extremely low optical flux is not provided by broadband bright squeezed vacuum. In the opposite case that the final-state linewidth is much broader than the bandwidth of the BSV exciting light, we show that the TPA rate is proportional to the second-order intensity autocorrelation function at zero time delay ${g}^{(2)}(0)$, as expected. We derive and evaluate formulas describing the transition between these two limiting cases, that is, including the regime where the molecular linewidth and optical bandwidth are comparable, as is often the case in experimental studies. We also show that for ${g}^{(2)}(0)$ to reach the idealized form ${g}^{(2)}(0)=3+1/\overline{n}$, with $\overline{n}$ being the mean number of photons per temporal mode, it is required to compensate the dispersion inherent in the nonlinear-optical crystal used to generate the BSV.

Beyond photon pairs—nonlinear quantum photonics in the high-gain regime: a tutorial

Integrated optical devices will play a central role in the future development of nonlinear quantum photonics. Here we consider the generation of nonclassical states of light within them with a focus on Gaussian states beyond the low-gain, single photon pair regime accurately described by perturbation theory. Starting from the solid foundation provided by Maxwell’s equations, we then move to applications by presenting a unified formulation that allows for a comparison of stimulated and spontaneous experiments in ring resonators and nanophotonic waveguides and leads directly to the calculation of the quantum states of light generated in high-gain nonlinear quantum photonic experiments.

The energy spread effects of an electron beam on the evolution of Cherenkov free-electron lasers

An analytical approach is presented to calculate the growth rate coefficient which describes the intensity evolution of a Cherenkov Free—Electron Laser (CFEL) operating in the linear high—gain regime. The effects of the energy spread on the growth rate of a CFEL are addressed by introducing a relaxation time in our analysis. The relaxation process is associated with a deviation of electron velocities from the average value due to an energy spread whatever its source. Therefore, the relaxation time can present a unified point of view to describe the gain deterioration caused by the inhomogeneous broadening of energy spread effects. In this study, the plasma fluid and Maxwell formulations are used to describe the dynamics of electrons. It is found that the growth rate coefficient is saturated at a maximum value when the interaction time is approximately five times the relaxation time. When the electron relaxation is neglected (i.e., the relaxation time is infinitely long), the gain expression derived by our approach agrees adequately with those reported in other studies. It is shown that our gain expression is generalized and simple enough to provide fast and reliable assessment of the performance of CFEL devices.

Quantum spatial dynamics of high-gain parametric down-conversion accompanied by cascaded up-conversion

Quantum cascaded up-conversion (CUpC) of parametric down conversion (PDC) in a finite nonlinear ${\ensuremath{\chi}}^{(2)}$ crystal is studied theoretically within parametric approximation. The exact solution for creation and annihilation operators presented in the form of Bogoliubov transformation is valid for the high-gain regime and explicitly includes the nonzero wave-vector mismatch both for PDC and CUpC. Characteristic equation is used to analyze parametric amplification and oscillating regimes for degenerate, three- and four-mode cases. We show that the parametric amplification exists under the fulfillment of the cascaded phase-matching conditions while both the PDC and CUpC processes are separately non-phase-matched. The influence of CUpC on quadrature squeezing of degenerate PDC is estimated.

Three-Dimensional, Time-Dependent Analysis of High- and Low-Q Free-Electron Laser Oscillators

Free-electron lasers (FELs) have been designed to operate over virtually the entire electromagnetic spectrum, from microwaves through to X-rays, and in a variety of configurations, including amplifiers and oscillators. Oscillators can operate in both the low and high gain regime and are typically used to improve the spatial and temporal coherence of the light generated. We will discuss various FEL oscillators, ranging from systems with high-quality resonators combined with low-gain undulators, to systems with a low-quality resonator combined with a high-gain undulator line. The FEL gain code MINERVA and wavefront propagation code OPC are used to model the FEL interaction within the undulator and the propagation in the remainder of the oscillator, respectively. We will not only include experimental data for the various systems for comparison when available, but also present, for selected cases, how the two codes can be used to study the effect of mirror aberrations and thermal mirror deformation on FEL performance.

Understanding High-Gain Twin-Beam Sources Using Cascaded Stimulated Emission

We present a new method for the spectral characterization of pulsed twin beam sources in the high gain regime, using cascaded stimulated emission. We show an implementation of this method for a ppKTP spontaneous parametric down-conversion source generating up to 60 photon pairs per pulse, and demonstrate excellent agreement between our experiments and our theory. This work enables the complete and accurate experimental characterization of high gain effects in parametric down conversion, including self and cross-phase modulation. Moreover, our theory allows the exploration of designs with the goal of improving the specifications of twin beam sources for application in quantum information, computation, sampling, and metrology.

Optical coherence tomography with a nonlinear interferometer in the high parametric gain regime

We demonstrate optical coherence tomography based on an SU(1,1) nonlinear interferometer with high-gain parametric downconversion. For imaging and sensing applications, this scheme promises to outperform previous experiments working at low parametric gain, since higher photon fluxes provide lower integration times for obtaining high-quality images. In this way, one can avoid using single-photon detectors or CCD cameras with very high sensitivities, and standard spectrometers can be used instead. Other advantages are higher sensitivity to small loss and amplification before detection so that the detected light power considerably exceeds the probing one.

Fusion energy

This paper presents an overview of the main challenges that fusion research is facing on the road to a demonstration power plant. The focus is on magnetic confinement fusion. Most of the challenges are being addressed in the context of the ITER construction and exploitation. These include the demonstration of high fusion gain regimes of operation, the management of high heat and particle loads and the integration of the main technologies of a fusion power plant. In preparation of DEMO, reliable solutions for the breeding blanket and neutron resistant materials have to be developed.

On the Performance of Quantum Key Distribution FSO Systems Under a Generalized Pointing Error Model

In this letter, the performance of a quantum key distribution (QKD) free-space optical (FSO) system is analyzed while taking a generalized pointing error model into account. More specifically, closed-form expressions for the average received powers at both the legitimate receiver and eavesdropper are derived. In addition, their corresponding asymptotic results valid in the high telescope gain regime are also presented. To capture the secure performance, we also investigate the ratio of received powers at the eavesdropper and at the legitimate receiver. Further, in some special cases, we find the optimal telescope gains for the received powers at both the legitimate receiver and eavesdropper, as well as the power ratio, which is important and useful for a secure QKD FSO system design. Finally, some selected numerical results are presented to illustrate the mathematical formalism and validate the accuracy of the derived analytical expressions.

Analytical approach to calculate the gain of Brillouin fiber amplifiers in the regime of pump depletion.

We provide an accurate analytic expression for the Brillouin fiber amplifiers (BFAs) gain in the regime of pump depletion. The solutions are divided into three parts. In the first part, we review the weak pump regime where the highly accurate second-order corrected undepleted-pump-approximation-based solution is adopted; in the high-gain regime where both the fiber loss and nonlinear term are nonnegligible effects and need to be accounted for along with the pump depletion; and in the saturation regime where the Stokes power is at the rear end exceeds critical power. We provide an accurate analytic expression for the BFA gain and show results of experimental validation. The presented analysis can be used to accurately predict the performance of Brillouin fiber amplifiers working in any regime.

Maximizing expected terminal utility of an insurer with high gain tax by investment and reinsurance

This paper investigates optimal investment and proportional reinsurance policies for an insurer who subjects to pay high gain tax. The surplus process of the insurer and the return process of the financial market are both modulated by the external macroeconomic environment. The dynamic of the external macroeconomic environment is specified by a Markov chain with finite states. Once the insurer’s accumulated profits attain a new maximum, they have to pay high gain tax. The objective of the insurer is to maximize the expected terminal utility by investment and reinsurance. The controlled wealth process of the insurer turned out to be a controlled jump diffusion process with reflections and Markov regime switching. By the weak dynamic programming principle (WDPP), we prove that the value function is the unique viscosity solution to the coupled Hamilton-Jacob-Bellman (HJB) equations with first derivative boundary constraints. By the Markov chain approximating method for the HJB equations, we construct a numerical scheme for approximating the viscosity solution to the coupled HJB equations. Two numerical examples are presented to illustrate the impact of both high gain tax and regime switching on the optimal policies.

A primary radiation standard based on quantum nonlinear optics

The spectrum of vacuum fluctuations of the electromagnetic field is determined solely from first physical principles and can be seen as a fundamental property that qualifies as a primary radiation standard. We demonstrate that the amplitude of these quantum fluctuations triggering nonlinear optical processes can be used as a reference for radiometry. In the spontaneous regime of photon pair generation, the shape of the emitted spectrum is nearly independent of laboratory parameters. In the high-gain regime, where spontaneous emission turns to stimulated emission, the shape of the frequency spectrum is uniquely determined by the number of created photons. Both aspects allow us to determine the quantum efficiency of a spectrometer over a broad range of wavelengths without the need of any external calibrated source or detector.

Optimal investment and dividend for an insurer under a Markov regime switching market with high gain tax

<p style='text-indent:20px;'>This study examines the optimal investment and dividend problem for an insurer with CRRA preference. The insurer's goal is to maximize the expected discounted accumulated utility from dividend before ruin and the insurer subjects to high gain tax payment. Both the surplus process and the financial market are modulated by an external Markov chain. Using the <i>weak dynamic programming principle</i> (WDPP), we prove that the value function of our control problem is the unique viscosity solution to coupled <i>Hamilton-Jacobi-Bellman</i> (HJB) equations with first derivative constraints. Solving an auxiliary problem without regime switching, we prove that, it is optimal for the insurer in a multiple-regime market to adopt the policies in the same way as in a single-regime market. The regularity of the viscosity solution on its domain is proved and thus the HJB equations admits classical solution. A numerical scheme for the value function is provided by the Markov chain approximation method, two numerical examples are given to illustrate the impact of the high gain tax and regime switching on the optimal policies.

Analytical approach of Brillouin amplification over threshold.

We report on an accurate closed-form analytical model for the gain of a Brillouin fiber amplifier that accounts for material loss in the depleted pump regime. We determined the operational model limits with respect to its relevant parameters and pump regimes through both numerical and experimental validation. As such, our results enable accurate performance prediction of Brillouin fiber amplifiers operating in the weak-pump, high-gain, and saturation regimes alike.

RF Energy Harvesting Based Multiple Access Relay Systems: A DMT Perspective

A multiple-access relay system, where the relay node is powered by radio frequency radiation is analyzed in this paper. Specifically, the focus is on the time-switching-based scheme in which the intermediate relay switches between the energy harvesting (EH), information decoding (ID), and the information re-transmission (TX). For this system, we have characterized the diversity-multiplexing trade-off (DMT) for two variants of the EH-based dynamic decode-and-forward (DDF) protocols: without feedback (EH-DDF) and with limited feedback (EH-DDF-LF). Analysis of the protocols reveals that the diversity gain of EH-DDF scheme is inferior to that of the traditional non-EH-based DDF protocol. Furthermore, the impact of energy harvesting duration on the DMT performance has been extensively investigated. Consequently, it is observed that the achievable diversity gain of the EH-DDF improves with the reduction in energy harvesting interval. However, there exists a performance difference between the classical non-EH-based DDF and EH-DDF even for the minute harvest duration. On the other hand, in the case of EH-DDF-LF, the performance approaches the diversity upper bound in the high multiplexing gain regime. Finally, a detailed comparison of the proposed EH-based schemes has been presented.

Generation of two-temporal-mode photon states by vector four-wave mixing

Photon pair states and multiple-photon squeezed states have many applications in quantum information science. In this paper, Green functions are derived for spontaneous four-wave mixing in the low- and high-gain regimes. Nondegenerate four-wave mixing in a strongly-birefringent medium generates signal and idler photons that are associated with only one pair of temporal (Schmidt) modes, for a wide range of pump powers and arbitrary pump shapes. The Schmidt coefficients (expected photon numbers) depend sensitively on the pump powers, and the Schmidt functions (shapes of the photon wavepackets) depend sensitively on the pump powers and shapes, which can be controlled.