Experimental nonclassicality of single-photon-added thermal light states

Alessandro Zavatta, Valentina Parigi, and Marco Bellini

Phys. Rev. A 75, 052106 – Published 10 May 2007

Abstract

We report the experimental realization and tomographic analysis of quantum light states obtained by exciting a classical thermal field by a single photon. Such states, although completely incoherent, possess a tunable degree of quantumness which is here exploited to put to a stringent experimental test some of the criteria proposed for the proof and the measurement of state nonclassicality. The quantum character of the states is also given in quantum information terms by evaluating the amount of entanglement that they can produce.

Received 17 March 2006

DOI:https://doi.org/10.1103/PhysRevA.75.052106

Authors & Affiliations

Alessandro Zavatta^1,2,*, Valentina Parigi^2,3, and Marco Bellini^1,3,†

¹Istituto Nazionale di Ottica Applicata (CNR), L.go E. Fermi, 6, I-50125, Florence, Italy
²Department of Physics, University of Florence, I-50019 Sesto Fiorentino, Florence, Italy
³LENS, Via Nello Carrara 1, 50019 Sesto Fiorentino, Florence, Italy

^*Electronic address: azavatta@inoa.it
^†Electronic address: bellini@inoa.it

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Issue

Vol. 75, Iss. 5 — May 2007

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Images

Figure 1
(Color online) Experimental setup. HR (HT) is a high reflectivity (transmittivity) beam splitter; SPCM is a single-photon-counting module; all other symbols are defined in the text. The mode-cleaning fiber used to inject the thermal state coming from the rotating ground glass disk (RD) into the parametric crystal is not shown here for clarity.Reuse & Permissions
Figure 2
(Color online) Experimentally reconstructed diagonal density matrix elements (reconstruction errors of statistical origin are of the order of 1%) and Wigner functions for thermal states (left) and SPATSs (right): (a) $\bar{n} = 0.08$ ; (b) $\bar{n} = 1.15$ . Filled circles indicate the density matrix elements calculated for thermal states and SPATSs with the expected efficiencies.Reuse & Permissions
Figure 3
(Color online) (a) Sections of the experimentally reconstructed Wigner functions for SPATSs with different $\bar{n}$ ; (b) experimental values for the minimum of the Wigner function $W (0)$ as a function of $\bar{n}$ for SPATSs (solid squares) and for single-photon Fock states (empty circles) obtained by blocking the injection; the values calculated from Eq. (8) for $η = 0.62$ (solid curves) are in very good agreement with experimental data and clearly show the appropriateness of the model. Negativity of the Wigner function is a sufficient condition for affirming the nonclassical character of the state.Reuse & Permissions
Figure 4
(Color online) Experimental characteristic functions involved in the RV nonclassicality criterion for the detected SPATSs: (a) first order; (b) second order (the inset shows a magnified view of the region where the state with $\bar{n} = 0.53$ is just slightly fulfilling the criterion).Reuse & Permissions
Figure 5
(Color online) (a) Experimental data (squares) and calculated values (solid curve) of $B (0)$ as a function of $\bar{n}$ ; negative values indicate nonclassicality of the state. (b) The same as above for the entanglement potential (EP) of the SPATSs; here nonclassicality is demonstrated by EP values greater than zero.Reuse & Permissions
Figure 6
Calculated regions of nonclassical behavior of SPATSs as a function of $\bar{n}$ and $η$ according to (a) the negativity of the Wigner function at the origin $W (0)$ ; (b) the Klyshko criterion $B (0)$ ; (c) the entanglement potential EP. White areas indicate classical behavior; gray areas indicate where a potentially nonclassical character is not measurable due to experimental reconstruction noise (estimated as the average error on the experimentally reconstructed parameters); black areas indicate regions where the nonclassical character is measurable given the current statistical uncertainties.Reuse & Permissions

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