Average Photon Number Research Articles

Continuous-variable entanglement in a two-mode lossy cavity: An analytic solution

Continuous-variable (CV) entanglement is a valuable resource in the field of quantum information. One source of CV entanglement is the correlations between the position and momentum of photons in a two-mode squeezed state of light. In this paper, we theoretically study the generation of squeezed states, via spontaneous parametric downconversion (SPDC), inside a two-mode lossy cavity that is pumped with a classical optical pulse. The dynamics of the density operator in the cavity is modelled using the Lindblad master equation, and we show that the exact solution to this model is the density operator for a two-mode squeezed thermal state, with a time-dependent squeezing amplitude and average thermal photon number for each mode. We derive an expression for the maximum entanglement inside the cavity that depends crucially on the difference in the losses between the two modes. We apply our exact solution to the important example of a microring resonator that is pumped with a Gaussian pulse. The expressions that we derive will help researchers optimize CV entanglement in lossy cavities.

Can we control the amount of useful nonclassicality in a photon added hypergeometric state?

Non-Gaussianity inducing operations are studied in the recent past from different perspectives. Here, we study the role of photon addition, a non-Gaussianity inducing operation, in the enhancement of nonclassicality in a finite dimensional quantum state, namely hypergeometric state with the help of some quantifiers and measures of nonclassicality. We observed that measures to characterize the quality of single photon source and anticlassicality lead to the similar conclusion, i.e. to obtain the desired quantum features one has to choose all the state parameters such that average photon numbers remains low. Wigner logarithmic negativity of the photon added hypergeometric state and concurrence of the two-mode entangled state generated at the output of a beamsplitter from this state show that nonclassicality can be enhanced by increasing the state parameter and photon number addition but decreasing the dimension of the state. In principle, decreasing the dimension of the state is analogous to holeburning and is thus expected to increase nonclassicality. Further, the variation of Wigner function not only qualitatively illustrates the same features as observed quantitatively through concurrence potential and Wigner logarithimic negativity, but illustrate non-Gaussianity of the quantum state as well.

Improved phase sensitivity in a quantum optical interferometer based on multiphoton catalytic two-mode squeezed vacuum states

The usage of non-Gaussian states to improve the phase sensitivity of interferometers has been studied before. In this paper, we introduce the multiphoton catalysis two-mode squeezed vacuum (MC-TMSV) state as an input of the Mach-Zehnder interferometer (MZI) and study its phase sensitivity with photon-number parity measurement and the influence of photon losses. We also study the statistical properties of the MC-TMSV state in terms of the average photon number, the Wigner function, and the Mandel-$Q$ parameter. Our results show that the MC-TMSV state can exhibit stronger nonclassical characteristics, thereby making the phase sensitivity more precise with either the increase of the photon-catalyzed number or the decrease of the transmissivity. Furthermore, we also consider the effects of photon losses involving external- and internal-loss processes of the MZI, and we find that in both cases the sensitivity with the MC-TMSV state can be significantly better than that with the TMSV state under the same parameters especially in the serious photon losses and small initial squeezing regimes. We also find that the multiphoton catalysis is more sensitive to the external photon losses compared with the internal ones. Our results here can find important applications in quantum metrology.

An average photon number measurement scheme based on balanced homodyne detection

<sec>Quantum key distribution (QKD) has become an alternative technology defensing the security threat resulting from quantum computing. Owing to its superiority in coexistence with optical infrastructures and cost-effective, continuous variable QKD (CV-QKD) is widely studied and developed towards the practical application stage. The standardized measurement of critical parameters of the system should be studied urgently.</sec><sec>In this work we propose a scheme based on balanced homodyne detection with phase-randomized local oscillator to realize the average photon number measurement. By controlling local oscillator phase positively, which obeys <inline-formula><tex-math id="M2">\begin{document}$ [0,\mathrm{ }2\mathrm{\pi }] $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20211216_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20211216_M2.png"/></alternatives></inline-formula> uniform distribution, a linear relationship between average photon numbers and the variance of detector output can be obtained in simulation and experiment. With high-accuracy (～0.1) photons/pulse and large range ～23 dB, this average photon number measurement scheme provides a great reference to evaluating the critical parameters of CV-QKD system in the practical process.</sec>

Full-waveform fast correction method for photon counting Lidar

The first photon bias of photon detection results in distortion of the photon waveform, which seriously affects the accurate acquisition of target information. A rapid universal recursive correction method is proposed, which is suitable for multi-trigger and single-trigger modes of photon detection. The calculation time is 2 to 3 orders of magnitude faster than that of Xu et al.’s method. In the experiment, we have obtained good correction results for area targets and targets with varying depths. When the average number of echo photons is 0.89, the correlation distance of the correction waveform is reduced by 85%.

Atomic population transfer for single- and N-photon wavepackets

We investigate the most energy-efficient way to transfer population in a three-level atom in the lambda configuration, under conditions of very strong coupling to a one-dimensional waveguide. We start with the ideal situation in which a single-photon pulse can yield a perfect transfer, through the process known as “single-photon Raman interaction,” and then consider how to improve the transfer probability by adding as few photons as possible when these ideal conditions are not met. We find that under a broad range of conditions, the failure probability can be made to decrease exponentially with the average number of photons in a coherent-state wavepacket. We also find that, in general, under these conditions, it is preferable to increase the number of photons in the single “pump” pulse than to add a second (“Stokes”) pulse on the second leg of the lambda configuration.

Intense green upconversion emission by photon avalanche process from Er3+/Yb3+ co-doped NaBi(WO4)2 phosphor

The Er3+/Yb3+ co-doped NaBi(WO4)2 (NBW) phosphor has been synthesized by conventional solid state reaction technique. The XRD analysis confirms the tetragonal crystal structure of NaBi(WO4)2. An intense green upconversion (UC) emission by photon avalanche (PA) process has been observed under excitation with 980 nm laser at room temperature. The observed green emission is due to 2H11/2, 4S3/2→4I15/2 (523, 548 nm) transitions of Er3+ ion. The green emission dominate because the intensities of other peaks are very small. The average number of photons involved in the UC process is 8.4 for 523 nm emission, the rise time of 2H11/2 level decreases with increasing the laser power and the power versus emission intensity plot is concave type. These are the characteristics of PA process. The PA process has been explained by looping energy transfer mechanism. In the present case, the PA appeared at very low power (<30 mW). This material may be applicable in intense green emission, finger printing, green component of white light and other optical devices.

Geant4 quartz fiber simulations as part of luminometer development for CMS

Measurements of luminosity are required to be exceedingly accurate for the new upcoming era of the LHC with higher energies and a more complex structure of the beam (HL-LHC). A new device is being developed for the CMS experiment to fulfill demands of being stand-alone and precise. The paper describes the design, main components and physics behind the new quartz fiber based luminometer (QFL). Via simulations of a single quartz fiber, we were able to calculate an average number of photons reaching the end of the fiber after a single particle hit.

Multiphoton-Absorption-Excited Up-Conversion Luminescence in Optical Fibers

We experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation.

Ultrafast carrier dynamics in double perovskite Cs2AgBiBr6 nanocrystals

The photon flux-dependent transient absorption spectroscopy is employed to investigate the carrier dynamics of Cs2AgBiBr6 nanocrystals (NCs), exhibiting that the hot carrier cooling, the self-trapping process, the surface defect capture and the carrier recombination together participate in the carrier relaxation process after photoexcitation. The evolution of their lifetimes as a function of 〈N〉 (average photon number per nanocrystal) all show two stages. Moreover, the role of HC in the subsequent carrier dynamics is also discussed. These results can help explain the carrier dynamics in the double perovskite NCs for designing and optimizing the perovskite-based optoelectronic devices with high performance.

Characterization of quantum squeezing generated from the phase-sensitive and phase-insensitive amplifiers in the ultra-low average input photon number regime.

We give the general expressions of intensity-difference squeezing (IDS) generated from two types of optical parametric amplifiers [i.e. phase-sensitive amplifier (PSA) and phase-insensitive amplifier (PIA)] based on the four-wave mixing process, which clearly shows the IDS transition between the ultra-low average input photon number regime and the ultra-high average input photon number regime. We find that both the IDS of the PSA and the IDS of the PIA get enhanced with the decrease of the average input photon number especially in the ultra-low average input photon number regime. This result is substantially different from the result in the ultra-high average input photon number regime where the IDS does not vary with the average input photon number. Moreover, under the same intensity gain, we find that the optimal IDS of the PSA is better than the IDS of the PIA in the ultra-low average input photon number regime. Our theoretical work predicts the presence of strong quantum correlation in the ultra-low average input photon number regime, which may have potential applications for probing photon-sensitive biological samples.

Preparation of nonclassical states by displacement-based quantum scissors

We theoretically study the statistical properties of non-Gaussian states generated by inputting coherent state, single-mode squeezed vacuum state and thermal state to the displacement-based single-side quantum scissor. Compared to the case without the displacement, it is shown that the displacement-based single-side quantum scissor with large coherent amplitudes can not only effectively enhance the success probability of quantum state preparation in the high-transmittance range, but also improve the statistical properties of the generated states involving the average photon number, the signal to noise ratio and the nonclassicality. These results indicate that the usage of the displacement-based single-side quantum scissor may have potential applications for the optical interferometry.

Integrated-Photonic Characterization of Single-Photon Detectors for Use in Neuromorphic Synapses

We show several techniques for using integrated-photonic waveguide structures to simultaneously characterize multiple waveguide-integrated superconducting-nanowire detectors with a single fiber input. The first set of structures allows direct comparison of detector performance of waveguide-integrated detectors with various widths and lengths. The second type of demonstrated integrated-photonic structure allows us to achieve detection with a high dynamic range. This device allows a small number of detectors to count photons across many orders of magnitude in count rate. However, we find a stray light floor of -30 dB limits the dynamic range to three orders of magnitude. To assess the utility of the detectors for use in synapses in spiking neural systems, we measured the response with average incident photon numbers ranging from less than $10^{-3}$ to greater than $10$. The detector response is identical across this entire range, indicating that synaptic responses based on these detectors will be independent of the number of incident photons in a communication pulse. Such a binary response is ideal for communication in neural systems. We further demonstrate that the response has a linear dependence of output current pulse height on bias current with up to a factor of 1.7 tunability in pulse height. Throughout the work, we compare room-temperature measurements to cryogenic measurements. The agreement indicates room-temperature measurements can be used to determine important properties of the detectors.

Cascaded Second Harmonic Generation with a Half-Order Periodical Orientation

We demonstrate theoretically cascaded fourth and second harmonics generation in a periodically oriented nonlinear crystal with a half-order of the periodical orientation. We consider a cascaded process in which four photons of the fundamental harmonic are initially converted into an intermediate photon of the fourth harmonic, which parametrically decays at the second stage into two photons of the second harmonic. We show that fractional phase matching can be achieved by using an asymmetric periodically poled grating. To describe the propagation and transformation of light inside a nonlinear crystal, the quantum spatial Heisenberg equations have been applied, using which the average numbers of photons of the fourth and second harmonics have been calculated as functions of the nonlinear crystal length.

Equivalence of approximate Gottesman-Kitaev-Preskill codes

The Gottesman-Kitaev-Preskill (GKP) quantum error correcting code attracts much attention in continuous variable (CV) quantum computation and CV quantum communication due to the simplicity of error correcting routines and the high tolerance against Gaussian errors. Since the GKP code state should be regarded as a limit of physically meaningful approximate ones, various approximations have been developed until today, but explicit relations among them are still unclear. In this paper, we rigorously prove the equivalence of these approximate GKP codes with an explicit correspondence of the parameters. We also propose a standard form of the approximate code states in the position representation, which enables us to derive closed-from expressions for the Wigner functions, the inner products, and the average photon numbers in terms of the theta functions. Our results serve as fundamental tools for further analyses of fault-tolerant quantum computation and channel coding using approximate GKP codes.

Two-mode Gaussian states as resource of secure quantum teleportation in open systems

For secure quantum teleportation (SQT) of coherent states two conditions are necessary to be fulfilled: Gaussian-state resources with two-way steering and teleportation fidelity higher than 2/3. We investigate and compare squeezed thermal states and squeezed vacuum states as initial resource states for SQT in an open quantum system, consisting of two uncoupled harmonic oscillators interacting with a thermal environment. The evolution of the open system is obtained in terms of the covariance matrix, by using the Gorini-Kossakowski-Lindblad-Sudarshan master equation. The SQT conditions are satisfied in a longer period of time in the case of initial squeezed vacuum states, therefore these states are better resource states for SQT than squeezed thermal states. We show that the admissible time for SQT decreases by increasing temperature, dissipation coefficient and average number of thermal photons, while for greater values of the squeezing parameter, SQT conditions are satisfied in a longer period of time.

Inclusive probability of particle creation on classical backgrounds

The quantum theories of boson and fermion fields with quadratic nonstationary Hamiltoanians are rigorously constructed. The representation of the algebra of observables is given by the Hamiltonian diagonalization procedure. The sufficient conditions for the existence of unitary dynamics at finite times are formulated and the explicit formula for the matrix elements of the evolution operator is derived. In particular, this gives the well-defined expression for the one-loop effective action. The ultraviolet and infrared divergencies are regularized by the energy cutoff in the Hamiltonian of the theory. The possible infinite particle production is regulated by the corresponding counterdiabatic terms. The explicit formulas for the average number of particles N_D recorded by the detector and for the probability w(D) to record a particle by the detector are derived. It is proved that these quantities allow for no-regularization limit and, in this limit, N_D is finite and w(D)in [0,1). As an example, the theory of a neutral boson field with stationary quadratic part of the Hamiltonian and nonstationary source is considered. The average number of particles produced by this source from the vacuum during a finite time evolution and the inclusive probability to record a created particle are obtained. The infrared and ultraviolet asymptotics of the average density of created particles are derived. As a particular case, quantum electrodynamics with a classical current is considered. The ultraviolet and infrared asymptotics of the average number of photons are derived. The asymptotics of the average number of photons produced by the adiabatically driven current is found.

Chaotic state as an output of vacuum state evolving in diffusion channel and generation of displaced chaotic state for quantum controlling* *Project supported by the Natural Science Fund of the Education Department of Anhui Province, China (Grant No. KJ2016A590), the Talent Foundation of Hefei University, China (Grant No. 15RC11), the Science Fund of Hefei University, China (Grant No. 2016dtr02), the

We show that chaotic state can be produced as an output of vacuum state evolving in diffusion channel, while displaced chaotic state is output of a coherent state evolving in diffusion channel. We also introduce the thermo vaccum state for the displaced chaotic state and evaluate the average photon number. The displaced chaotic state may be used exhibiting quantum controlling.

Criticality in two-mode interferometers

To achieve the optimal phase sensitivity in two-mode interferometers, one key problem is how to distribute photons between the two input ports, given a fixed total average photon number. In both the $\text{SU}(2)$ and $\text{SU}(1,1)$ interferometers with a product of coherent and Fock states as inputs, we find there exists a critical value of the total photon number, below which the optimal phase sensitivity can be achieved with the second port being the vacuum state. The critical points can be analytically fixed. We further consider a more general input state as a product of coherent and squeezed Fock states. Then we analytically identify three regions in the parameter space, similar to a phase diagram, and find that critical phenomena occur in two regions. If the total average input photon number is less than the critical value, the optimal distribution tends to minimize the average photon number in the second port. Our finding indicates that, in order to get interferometers with high sensitivity, one must carefully choose the photon number distribution according to the value of the input total average photon number. This central result will be useful in theoretical studies in the field of quantum parameter estimation.

Generation of Entanglement between Two Two-Level Atoms Coupled to a Microtoroidal Cavity Via Thermal Field

We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole interacting atoms coupled to a microtoroidal resonator. Each atom is individually coupled with the two counter-propagating whispering gallery modes of the resonator through their evanescent fields. The atom-atom entanglement shown for several parameter sets of the system was obtained using the negativity. For ideal resonators, it is seen that the entanglement is correlated to the dipole-dipole interaction and the average number of photons when the modes of the resonator are prepared in a thermal state even at high temperatures. Further, for the non-ideal resonator case, where there is a small structural deformation of the microtoroidal structure that allows a direct coupling between the modes, a counter-intuitive result is presented. The imperfections also offer the advantage of generating maximally entangled states for a two-atom subsystem with maximum fidelity.