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Quantum Measurements and Quantum Metrology

Intensity correlations from linear interactions

Matteo Bina, Stefano Olivares

Published Jan 30, 2014• 1 citation
Publisher

Abstract

Abstract We address the generation of intensity correlations arising from the interference between two optical states interacting through a beam splitter. We consider both phase insensitive and sensitive states and write the intensity correlations as functions of the mean number of photons and field quadratures of the input states. In particular we consider Fock number states and squeezed states as a paradigm of non-classical states and mixture of coherent states, which can be experimentally accessible. We show that, under certain conditions on the input states, intensity correlations may vanish or turn into anticorrelations.

DOI
10.2478/qmetro-2014-0004

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Abstract We address the generation of intensity correlations arising from the interference between two optical states interacting through a beam splitter. We consider both phase insensitive and sensitive states and write the intensity correlations as functions of the mean number of photons and field quadratures of the input states. In particular we consider Fock number states and squeezed states as a paradigm of non-classical states and mixture of coherent states, which can be experimentally accessible. We show that, under certain conditions on the input states, intensity correlations may vanish or turn into anticorrelations.
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Abstract In this paper, we investigate the creation of quantum correlations such as entanglement, the Gaussian quantum discord and quantum steering in a quantum system under consideration via the linear beam splitter with squeezed thermal and a single-mode Gaussian states at the inputs. This quantum system generates bright entangled output two-mode light. Specifically, the quantum entanglement can be enhanced through increasing the purity of the Gaussian state and the squeezing parameter at the input states. The quantum correlations reveal similar characteristics for each case. That means when we increase the non-classicality, purity and squeezing parameter, the quantum correlations show enhanced profile. On the other hand, upon increasing the mean thermal photon number at the input, the quantum correlations indicate inverse relation.
It has been known for a while that coherent high-intensity photon number eigenstate fields can be generated through nonlinear optical parametric processes,1 the same ones that give rise to quadrature squeezing.2,3 In contrast to quadrature squeezing which is essentially a single-mode phenomenon, although it is widely misunderstood that it is a two-mode phenomenon, the generation of single-mode number states through three- or four-wave mixing depends on two separate signal and idler modes that are perfectly correlated in photon numbers, in other words a twin beam. The nature of such twin beams is elucidated in both the Schrodinger and the Heisenberg pictures. In particular, it is shown that strong photon number correlation in a twin beam can still be obtained in an amplifier rather than an oscillator configuration, another widely missed point.
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We report preparation and characterization of coherent superposition states t[0>+alpha]1> of the electromagnetic field by conditional measurements on a beam splitter. This state is generated in one of the beam splitter output channels if a coherent state [alpha> and a single-photon Fock state [1> are present in the two input ports and a single photon is registered in the other beam splitter output. The single photon thus plays a role of a "catalyst:" it is explicitly present in both the input and the output channels of the interaction yet facilitates generation of a nonclassical state of light.
The second-order coherence of optical fields at output ports of a beam splitter is investigated. The properties of the second-order coherence are not only strongly dependent on the input states but also quite involved with the nature of the beam splitter. When parameters of both the input states and the beam splitter are chosen appropriately, the fields at the output ports will exhibit quantum behaviour. Between the two output modes, there stands mode–mode correlation which can even be anticorrelation. Some nonclassical properties, such as the photon antibunching effect of the input fields, may be destroyed by the beam splitter.