arXiv subjects

Jan Perina Jr

Publications and source records attributed to Jan Perina Jr.

At least 19 recordsLinked to original sources

arXiv2025

Two- and three-mode squeezing in a three-qubit entangled system

The states of a three-mode bosonic system with the restricted Hilbert space are discussed in the context of quantum entanglement and squeezing of quantum fluctuations. The states exhibiting non-zero tripartite entanglement are considered. Mutual relations between the two- and three-mode entanglement quantified by the corresponding negativities and the squeezing described by the corresponding principal squeeze variances are revealed. Entangled three-qubit states exhibiting squeezing are identified.

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arXiv2023

Quantification of Quantum Correlations in Two-Beam Gaussian States Using Photon-Number Measurements

Identification, and subsequent quantification of quantum correlations, is critical for understanding, controlling, and engineering quantum devices and processes. We derive and implement a general method to quantify various forms of quantum correlations using solely the experimental intensity moments up to the fourth order. This is possible as these moments allow for an exact determination of the global and marginal impurities of two-beam Gaussian fields. This leads to the determination of steering, tight lower and upper bounds for the negativity, and the Kullback-Leibler divergence used as a quantifier of state nonseparability. The principal squeezing variances are determined as well using the intensity moments. The approach is demonstrated on the experimental twin beams with increasing intensity and the squeezed super-Gaussian beams composed of photon pairs. Our method is readily applicable to multibeam Gaussian fields to characterize their quantum correlations.

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arXiv2022

Quantum Liouvillian exceptional and diabolical points for bosonic fields with quadratic Hamiltonians: The Heisenberg-Langevin equation approach

Equivalent approaches to determine eigenfrequencies of the Liouvillians of open quantum systems are discussed using the solution of the Heisenberg-Langevin equations and the corresponding equations for operator moments. A simple damped two-level atom is analyzed to demonstrate the equivalence of both approaches. The suggested method is used to reveal the structure as well as eigenfrequencies of the dynamics matrices of the corresponding equations of motion and their degeneracies for interacting bosonic modes described by general quadratic Hamiltonians. Quantum Liouvillian exceptional and diabolical points and their degeneracies are explicitly discussed for the case of two modes. Quantum hybrid diabolical exceptional points (inherited, genuine, and induced) and hidden exceptional points, which are not recognized directly in amplitude spectra, are observed. The presented approach via the Heisenberg-Langevin equations paves the general way to a detailed analysis of quantum exceptional and diabolical points in infinitely dimensional open quantum systems.

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arXiv2022

Non-classicality criteria for N-dimensional optical fields detected by quadratic detectors

Non-classicality criteria for general N-dimensional optical fields are derived. They involve intensity moments, the probabilities of photon-number distributions or combinations of both. The Hillery criteria for the sums of the probabilities of even or odd photon numbers are generalized to N-dimensional fields. As an example, the derived non-classicality criteria are applied to an experimental 3-mode optical field containing two types of photon-pair contributions. The accompanying non-classicality depths are used to mutually compare their performance.

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arXiv2021

Compound twin beams without the need of genuine photon-number-resolving detection

The scheme for building stronger multi-mode twin beams from a greater number of identical twin beams sufficiently weak so that single-photon sensitive on/off detectors suffice in their detection is studied. Statistical properties of these compound twin beams involving the non-classicality are analyzed for intensities up to hundreds of photon pairs. Their properties are compared with those of the genuine twin beams that require photon-number-resolving detectors in their experimental investigations. The use of such compound twin beams for the generation of sub-Poissonian light and measurement of absorption with sub-shot-noise precision is analyzed. A suitable theoretical model for the compound twin beams is developed to interpret the experimental data.

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arXiv2021

Two-beam light with simultaneous anticorrelations in photon-number fluctuations and sub-Poissonian statistics

Two twin beams with a shared signal beam and separated idler beams are used together with the photon-number-resolving postselection in the signal beam to arrive at two coupled beams with anticorrelations in photon-number fluctuations. Moreover, the beams exhibit the sub-Poissonian photon-number statistics in their marginal distributions under suitable conditions. The postselected fields with the increasing mean photon numbers are reconstructed from the experimental photocount histograms by the maximum likelihood approach. Also a suitable Gaussian fit of both original twin beams and simulation of the postselection process are applied to arrive at the corresponding photon-number distributions. Their nonclassical properties are analyzed by suitable nonclassicality criteria and quantified by the corresponding nonclassicality depths. Determining the appropriate quasi-distributions of integrated intensities with negative values, the performance of different nonclassicality criteria is judged. Properties of the postselected fields reached both by the used and ideal photon-number-resolved detectors are mutually compared.

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arXiv2021

Ideal pairing of the Stokes and anti-Stokes photons in the Raman process

A quantum model of the Raman process with the independent Stokes and anti-Stokes nonlinear interactions is developed to study nonclassical correlations between the photons in the Stokes and anti-Stokes fields. The role of the laser pump amplitude, the ratio of the Stokes and anti-Stokes coupling constants and the population and losses of the vibrational mode in forming the correlations is elucidated. The $ g^{(2)} $ intensity cross-correlation function, noise-reduction-factor, two-mode principal squeezing variance, logarithmic negativity, non-classicality depth, steering parameter and the Bell parameter are analyzed side-by-side to shed light to the correlations between the Stokes and anti-Stokes fields. Conditions for having the Stokes and anti-Stokes fields composed of only photon pairs, similarly as it occurs in twin beams in parametric down-conversion, are revealed. They allow for nonzero mean thermal phonon numbers.

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arXiv2020

Non-classicality and entanglement criteria for bipartite optical fields characterized by quadratic detectors II: Criteria based on probabilities

Numerous non-classicality criteria based on the probabilities of experimental photocount or theoretical photon-number distributions are derived using several approaches. Relations among the derived criteria are revealed and the fundamental criteria are identified. They are grouped into parametric systems that allow the analysis of the non-classicality from different points of view ('local' non-classicality, pairwise character of photon correlations, etc.). Considering their structure, the criteria may be divided into groups that differ in the power to resolve the non-classicality. Quantification of the non-classicality using the Lee non-classicality depth and the non-classicality counting parameter is discussed. The used number of field's modes is identified as an important parameter that may cause unexpected results. An appropriate linear transformation of a photocount (photon-number) distribution into its s-ordered form, needed for the determination of the non-classicality depth, is derived. For comparison, the derived criteria are applied both to an experimental photocount histogram of a twin beam and the reconstructed photon-number distributions with different levels of the noise.

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arXiv2020

Waves in intensity coherence of evolving intense twin beams

Strong correlations between the signal and idler beams imprinted during their generation dominantly determine the properties of twin beams. They are also responsible for the waves in intensity coherence observed in the wave-vector space of a twin beam propagating in a nonlinear crystal in the regime with pump depletion. These waves start to develop at certain twin-beam intensity and move from the signal and idler beam centers towards their tails. They manifest themselves via the change of coherence volume monitored in the far field by the measurement of local modified $ \bar{g}^{(2)} $ function, which acts as a sensitive and stable tool for investigating field intensity coherence.

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arXiv2018

Reconstruction of joint photon-number distributions of twin beams incorporating spatial noise reduction

A method for reconstructing joint photon-number distributions of twin beams from the experimental photocount histograms is suggested and experimentally implemented. Contrary to the standard reconstruction methods, it incorporates spatial noise reduction based on spatial pairing of photons. Superior performance of the method above the usual one for the maximum-likelihood approach is demonstrated.

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arXiv2017

Noise reduction in photon counting by exploiting spatial correlations

Joint photocount distributions of a weak twin beam acquired by an iCCD camera are analyzed with respect to the beam spatial correlations. A method for extracting these correlations from the experimental joint photocount distributions is suggested using a suitable statistical model that quantifies the contribution of spatial correlations to the joint photocount distributions. In detail, the profile of twin-beam intensity spatial cross-correlation function is revealed from the curve that gives the genuine mean photon-pair number (both photons from a pair are detected) as a function of the extent of the detection area. Also, the principle of reducing the noise in photon-number-resolving detection by using spatial correlations is experimentally demonstrated.

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arXiv2017

Nonclassicality and entanglement criteria for bipartite optical fields characterized by quadratic detectors

Numerous inequalities involving moments of integrated intensities and revealing nonclassicality and entanglement in bipartite optical fields are derived using the majorization theory, non-negative polynomials, the matrix approach, as well as the Cauchy-Schwarz inequality. Different approaches for deriving these inequalities are compared. Using the experimental photocount histogram generated by a weak noisy twin beam monitored by a photon-number-resolving iCCD camera the performance of the derived inequalities is compared. A basic set of ten inequalities suitable for monitoring the entanglement of a twin beam is suggested. Inequalities involving moments of photocounts (photon numbers) as well as those containing directly the elements of photocount (photon-number) distributions are also discussed as a tool for revealing nonclassicality.

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arXiv2017

Higher-order sub-Poissonian-like nonclassical fields: Theoretical and experimental comparison

Criteria defining higher-order sub-Poissonian-like fields are given using five different quantities: moments of (I) integrated intensity, (II) photon number, (III) integrated-intensity fluctuation, (IV) photon-number fluctuation, and (V) elements of photocount and photon-number distributions. Relations among the moment criteria are revealed. Performance of the criteria is experimentally investigated using a set of potentially sub-Poissonian fields obtained by post-selection from a twin beam. The criteria based on moments of integrated intensity and photon number and those using the elements of photocount distribution are found as the most powerful. States nonclassical up to the fifth order are experimentally reached in the former case, even the ninth-order non-classicality is observed in the latter case.

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arXiv2016

Coherent light in intense spatio-spectral twin beams

Intense spatio-spectral twin beams generated in the regime with pump depletion are analyzed applying a suggested quantum model that treats the signal, idler and pump fields in the same way. The model assumes the signal and idler fields in the form of the generalized superposition of signal and noise and reveals nonzero signal coherent components in both fields, contrary to the models developed earlier. The influence of coherent components on the properties of intense twin beams is elucidated. The interference pattern formed in the process of sum-frequency generation and that of the Hong-Ou-Mandel interferometer are shown to be able to experimentally confirm the presence of coherent components.

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arXiv2016

Spatial, spectral and temporal coherence of ultra-intense twin beams

Using the model of parametric interaction based on the spatio-spectral Schmidt modes and generalized parametric approximation, we analyze coherence and mode structure of ultra-intense twin beams generated in the regime with pump depletion. We show that the increase of spatial and spectral coherence with the increasing pump power observed for moderate powers is replaced by the decrease for the pump powers at which pump depletion occurs. This behavior of coherence is opposed to that exhibited by the number of spatio-spectral modes effectively constituting the twin beam. The conditions for maximal coherence are analyzed considering pump-beam parameters (spectral width, transverse radius). The existence of additional coherence maxima occurring at even higher pump powers is predicted and explained by the oscillatory evolution of the modes' populations.

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arXiv2015

Coherence and dimensionality of intense spatio-spectral twin beams

Spatio-spectral properties of twin beams at their transition from low to high intensities are analyzed in parametric and paraxial approximations using the decomposition into paired spatial and spectral modes. Intensity auto- and cross-correlation functions are determined and compared in the spectral and temporal domains as well as the transverse wave-vector and crystal output planes. Whereas the spectral, temporal and transverse wave-vector coherence increases with the increasing pump intensity, coherence in the crystal output plane is practically independent on the pump intensity owing to the mode structure in this plane. The corresponding auto- and cross-correlation functions approach each other for larger pump intensities. Entanglement dimensionality of a twin beam is determined comparing several approaches.

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arXiv2015

Coherence and mode decomposition of weak twin beams

Properties of weak spatio-spectral twin beams in paraxial approximation are analyzed using the decomposition into appropriate paired modes. Numbers of paired modes as well as numbers of modes in the signal (or idler) field in the transverse wave-vector and spectral domains are analyzed as functions of pump-beam parameters. Spatial and spectral coherence of weak twin beams is described by auto- and cross-correlation functions. Relation between the numbers of modes and coherence is discussed.

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arXiv2013

Optimal sub-Poissonian light generation from twin beams by photon-number resolving detectors

We generate nonclassical conditional states by exploiting the quantum correlations of multi-mode twin-beam states endowed with a sizeable number of photons. A strong relation between the sub-shot-noise correlations exhibited by twin beams and the sub-Poissonian character of the conditional states is experimentally revealed. It determines optimal conditions for sub-Poissonian light generation.

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