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Conference on Lasers and Electro-Optics

Conditional measurement of the photon number optical pulse collision

Friedrich König, T. Rechtenwald, M. Zielonka, R. Steidl, Gerd Leuchs, Andreas Sizmann

Published Aug 29, 2005• 0 citations

Abstract

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.

DOI: 10.1109/iqec.2000.907785

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The collision of two optical solitons, one a probe and the other a signal, writes out the energy of the signal soliton as a phase shift of the probe soliton. Consequently, a readout of the probe phase shift gives the photon number of the signal soliton. If the collision takes place in a low-loss optical fiber with the usual Kerr nonlinearity, the photon number of the signal soliton is preserved, and the measurement can be a quantum nondemolitional (QND) measurement. We describe experimental progress towards soliton collision QND measurements. We have collided two solitons at 1.460 nm (probe) and 1.463 nm (signal) and with the help of a delayed reference soliton (identical to the probe) in a homodyne detector system, we have measured the resulting probe soliton phase shifts. Toward a QND measurement, we correlate the shot noise fluctuations of the signal soliton with the corresponding phase noise fluctuations written on the probe. We present our current results.

Summary form only given. Quantum-nondemolition (QND) measurements are those that do not disturb the quantum distribution of the variable being measured. It has been experimentally demonstrated that QND measurement of the photon number an be achieved by use of wavelength-multiplexed soliton collisions. A quantum analysis of the experiment has also been developed. It was found that the phase spreading of the probe as a result of self-phase modulation can contribute significant noises. In this paper we propose a new and better QND scheme using cross-polarized soliton collisions in a fiber loop interferometer. The scheme requires only a single wavelength laser source and can be fully fiber-integrated, and, most importantly, the noise caused by self-phase modulation is automatically suppressed by detection of the squeezed quadrature of the probe soliton.

Summary form only given. Recent experiments have demonstrated more than 50% of photon number squeezing of optical pulses by spectral filtering method in nonlinear optical fibers. For such squeezing quantum correlations between the spectral components of the pulses play a crucial role. The intermode correlations in the squeezed pulses are mainly induced by the second-order dispersion and the third-order nonlinearity (the self-phase modulation (SPM) effect) of fibers. We numerically study the dependence of the initial pulse waveform on spectral filtering squeezing and the optimization of pulses to obtain the further squeezing. Calculations are performed by solving the quantum nonlinear Schrodinger equation (QNLSE) in the positive P representation.

We analyze schemes for performing quantum nondemolition (QND) measurements in optical cavities. We consider three schemes: (1) measurement of a quadrature phase amplitude using a parametric process, (2) measurement of a quadrature phase amplitude using the optical Kerr effect in a nonlinear fiber, and (3) measurement of the photon number also using the Kerr effect in a fiber. We show that in the second scheme an enhancement of the QND effect may be obtained by making the cavity finesse for the signal larger than that for the probe.