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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Observation of strong continuous-variable Einstein-Podolsky-Rosen entanglement using shaped local oscillators

Ami Shinjo, Naoyuki Hashiyama, Akane Koshio, Yujiro Eto, Takuya Hirano

Published Oct 24, 2016• 2 citations
Publisher

Abstract

The continuous-variable (CV) Einstein-Podolsky-Rosen (EPR) paradox and steering are demonstrated using a pulsed light source and waveguides. We shorten the duration of the local oscillator (LO) pulse by using parametric amplification to improve the temporal mode-matching between the entangled pulse and the LO pulse. After correcting for the amplifier noise, the product of the measured conditional variance of the quadrature-phase amplitudes is 0.74 < 1, which satisfies the EPR-Reid criterion.

DOI
10.1117/12.2241297

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The continuous-variable (CV) Einstein-Podolsky-Rosen (EPR) paradox and steering are demonstrated using a pulsed light source and waveguides. We shorten the duration of the local oscillator (LO) pulse by using parametric amplification to improve the temporal mode-matching between the entangled pulse and the LO pulse. After correcting for the amplifier noise, the product of the measured conditional variance of the quadrature-phase amplitudes is 0.74 < 1, which satisfies the EPR-Reid criterion.
We report an experimental demonstration of the continuous-variable Einstein-Podolsky-Rosen (EPR) paradox and quantum steering using a pulsed light source and nonlinear optical waveguides. In this pulsed light source experiment, time-domain measurements were performed in which one measured value of the quadrature phase amplitude of the light field was independently obtained for each pulse. This independence is useful for application to quantum information processing and fundamental physics. To realize time-domain measurements, in-house built homodyne detectors were used to detect individual pulses. In addition, to improve the temporal-mode matching between the local oscillator (LO) and entangled pulse, the duration of the LO pulse was shortened by single-pass optical parametric amplification. The product of the conditional variances of the quadrature amplitudes was 0.82 ± 0.09 < 1, which satisfies the condition for realization of the EPR paradox and quantum steering.
We demonstrated time-domain measurement and frequency domain measurement of continuous-variable (CV) entanglement with pulsed light source and waveguides. The experiment with pulsed light source has difficulty in temporal mode matching between the entangled beams and local oscillator (LO) beams. To break through this difficulty, we shorten the duration of LO pulse by optical parametric amplification (OPA) in a waveguide. We generated entanglement that satisfied EPR-Reid criterion in the time domain measurement.
A generalization of the 1935 Einstein-Podolsky-Rosen (EPR) argument for measurements with continuous variable outcomes is presented to establish criteria for the demonstration of the EPR paradox, for situations where the correlation between spatially separated subsystems is not perfect. Two types of criteria for EPR correlations are determined. The first type are based on measurements of the variances of conditional probability distributions and are necessary to reflect directly the situation of the original EPR paradox. The second weaker set of EPR criteria are based on the proven failure of (Bell-type) local realistic theories which could be consistent with a local quantum description for each subsystem. The relationship with criteria sufficient to prove entanglement is established, to show that any demonstration of EPR correlations will also signify entanglement. It is also shown how a demonstration of entanglement between two spatially separated subsystems, if not able to interpreted as a violation of a Bell-type inequality, may be interpreted as a demonstration of the EPR correlations. In particular it is explained how the experimental observation of two-mode squeezing using spatially separated detectors will signify not only entanglement but EPR correlations defined in a general sense.
Over the past three decades, numerous demonstrations of the violation of Bell’s inequalities have been reported in optical experiments based upon observations of polarization correlations for photon pairs. Without exception, these measurements as well as those in other systems have involved discrete variables for which the Bell inequalities are applicable. By contrast, an experiment to demonstrate the original proposal by Einstein, Podolsky, and Rosen (EPR)1 for a system of observables with a continuous spectrum has not previously been realized. From many possible theoretical avenues, we have followed the suggestion of Reid and Drummond2 to achieve a demonstration of the EPR paradox for continuous variables by employing a subthreshold optical parametric oscillator (OPO) operated in a frequency-degenerate but polarization-nondegenerate mode.