F. Konig

Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber.

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber 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 is 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.

Bulk Er:Yb:glass soliton femtosecond laser

Summary form only given. A bulk solid state Er:glass laser can combine the advantages of existing Er:fiber lasers, i.e. femtosecond pulses, with pulse-width tunability and low phase noise. Moreover, the combination of low-cost glass and pumping-by a relatively low-power diode laser is competitive to other bulk gain materials, e.g. Cr:YAG crystals using a pump power of several Watts, working at the eyesafe and telecommunications wavelength around 1.5 gin. However, the shortest pulses reported for a bulk Er:glass laser were limited to 2.5 ps. To overcome the limitation to the picosecond regime we increased the intracavity self-phase modulation in order to achieve soliton modelocking. This was realized by the insertion of an additional Kerr medium in the focal region of the resonator.

Fibre-optic photon-number squeezing in the normal group-velocity dispersion regime

Abstract The nonlinear optical Kerr effect, acting on optical pulses in fibres, creates spectral sidebands and noise correlations between these sidebands. The reduction of photon-number fluctuations of these pulses below the shot-noise limit by spectral filtering is well established in the anomalous dispersion regime which allows for soliton formation. Here it is demonstrated that a significant quantum-noise reduction with spectral filtering can also be reached for pulses in the normal dispersion regime. The filter function was optimized and the power dependence of the noise reduction was investigated. The best squeezing result is (1.2 ± 0.2) dB (corresponding to (2.6 ± 0.7) dB inferred for 100% detection efficiency).

Soliton backaction-evading measurement using spectral filtering

We report on a backaction-evading (BAE) measurement of the photon number of fiber-optical solitons operating in the quantum regime. We employ a recently proposed different detection scheme based on spectral filtering of colliding optical solitons. The measurements of the BAE criteria demonstrate significant quantum state preparation and transfer of the input signal to the signal and probe outputs exiting the apparatus, displaying the quantum-nondemolition behavior of the experiment.

Quantum Solitons in Optical Fibres: Basic Requisites for Experimental Quantum Communication

Continuous variable quantum entanglement emerges from nonlinear interactions of: fibre optical solitons in combination with some linear operation. We describe the detection and characterization of bright EPR-entanglement and QND-entanglement produced in this way and discuss the prospects of bright-beam-based quantum communication.

Conditional measurement of the photon number optical pulse collision

Summary form only given. The optical Kerr effect of fibers produced unique nonclassical correlations through intensity-dependent phase shifts in a variety of quadrature-amplitude squeezing and quantum-nondemolition (QND) experiments. Later, a new squeezing mechanism was observed with spectral filtering of fiber-optical pulses. Our novel QND approach applies spectral filtering to two interacting pulses in order to obtain a QND readout that is immune to phase noise. In a pulse collision the spectral separation between the center frequencies of the pulses is transiently enhanced, with the spectral shift of one (meter) pulse depending on the photon number of the other (signal) pulse. Thus photon-number fluctuations of one pulse are transferred to frequency fluctuations of the other pulse which are directly detectable after a spectral filter. The maximum frequency shift occurs in the center of the collision, where the pulses are well separated in frequency space, even if there is a spectral overlap before the collision.

Spectral quantum noise correlations of fiber-optic solitons

Spectral filtering of optical solitons has been demonstrated to squeeze their photon-number uncertainty up to a measured value of 3.8 dB. The squeezing has been explained in terms of an uneven spectral distribution of photon-number noise caused by the Kerr nonlinearity of the fiber. Some indication for correlations among different frequency components has been found in a numerical analysis. We present the first experimental evidence for such spectral correlations. The experimental setup is shown. Pulses of 130 fs centered at 1.5 /spl mu/m are launched into a 2.9-m polarization-presenting single-mode optical fiber with energies close to the fundamental soliton energy.

Photon-number noise reduction from a nonlinear fiber-loop mirror

Nonlinear unbalanced antiresonant ring interferometers have been proposed to provide various optical functions. The nonlinear optical-loop mirror (NOLM) is such an unbalanced fiber interferometer for ultrafast all-optical processing. Recently, it was suggested that the nonlinear input-output behavior of this device might also deamplify photon-number noise of coherent pulses below the shot-noise limit. Here, we present experimental evidence for directly detectable squeezing from a NOLM.