The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We use ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect, the blue-shifting of light at a white-hole horizon. We also show by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fibre interferometer. The Kerr nonlinearity in the fibre is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures are measured to be 4.0 ± 0.2 (4.0 ± 0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80 ± 0.03 < 2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64 ± 0.08) is well below the EPR limit of unity.Since the original proposal of a Gedankenexperiment intending to show the incompleteness of quantum mechanics in 1935 [1], a number of schemes for generating the Einstein-Podolsky-Rosen (EPR) entanglement have been realized. The schemes range from the production of gamma-ray pairs from positron-electron annihilations [2], to proton pairs [3], to pairs of low-energy photons from atomic radiative cascade [4] and more recently to schemes involving optical parametric processes [5]. Most of these initial experiments utilized the entanglement as originally intended: to test the validity of quantum mechanics via either the violation of Bell inequality [4] or the demonstration of the EPR paradox [6]. Following the proposals of a myriad of quantum information schemes in recent years where entanglement is regarded as a basic requisite, the subject matter has experienced a resurgence of interest. The purposes of entanglement generation are now shifting to that of quantum information applications. Amongst these applications are the realization of quantum teleportation, the implementation of dense coding, quantum cryptography and other quantum communication schemes [7]. In view of these changing needs, it is desirable to explore simpler and more reliable alternatives for the generation of EPR entanglement.In this letter, we report on what is to our knowledge the first generation of EPR entanglement of photons that does not rely on any pair production process, such as those in the above-mentioned examples. Instead, the Kerr (χ (3) ) nonlinearity of an optical fibre is utilized to produce two amplitude squeezed beams, with the nonlinear interaction on each beam uncoupled to the other. To create the EPR entanglement, no additional nonlinear interaction is required. Instead, the amplitude squeezed beams are made to interfere at a 50/50 beam splitter [8]. In this vein sum squeezing is obtained for the amplitude quadratures and difference squeezing for the phase quadratures. The signs of these correlations are interchanged compared to those achieved in other systems. This fact may be of importance in applications involving the opto-mechanical coupling of radiation pressure [9]. Apart from the simplicity of our scheme, it also has the potential advantage of being integrable into existing fibre-optics communication networks.

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Optical solitons or solitonlike states shed light to blueshifted frequencies through a resonant emission process. We predict a mechanism by which a second propagating mode is generated. This mode, called negative resonant radiation, originates from the coupling of the soliton mode to the negative-frequency branch of the dispersion relation. Measurements in both bulk media and photonic-crystal fibers confirm our predictions.