EXPERIMENTAL TEST OF NONLOCAL REALISM USING A NEW FIBER-BASED,

POLARIZATION-ENTANGLED PHOTON-PAIR SOURCE

Matthew D. Eisaman, Elizabeth Goldschmidt, Jingyun Fan, and Alan Migdall

*Optical Technology
Division, National Institute of Standards and Technology*

*100 Bureau Drive,
Mail Stop 8441, Gaithersburg. MD 20899-8441*

*and*

*Joint Quantum
Institute, University of Maryland, MD 20742*

The success of many quantum-information applications demands entangled photon pairs emitted at a high rate, and in a single spatial mode with narrow spectral bandwidth to allow low-loss coupling and propagation in optical-fiber networks. We describe the realization of a high spectral brightness, broad wavelength coverage, single-spatial mode source of polarization-entangled photon pairs operated at room temperature. The source takes advantage of single-mode fiber optics, large two-photon production probability in a nonlinear microstructure fiber, low single-photon noise level, and the inherent stability provided by a Sagnac interferometer. With a modest average pump power (300 mW), we create all four Bell states with a detected two-photon coincidence rate of 7 kHz per bandwidth of 0.5 THz (0.9 nm) over a spectral range of more than 10 nm. We perform quantum-state tomography to reconstruct the density matrices of the states, with the fidelity of each Bell state measuring 95% or more.

In addition to being useful for quantum-information applications, this high-fidelity source of entangled photons can also be used for fundamental tests of quantum mechanics. Using polarization-entangled two-photon singlet states, we compare our measurements of two-photon polarization correlations to the predictions of quantum mechanics, and also to the predictions of certain local realistic and non-local realistic theories. Our measurements are consistent with quantum-mechanical predictions, resulting in a violation of Bell’s inequality in the Clauser-Horne-Shimony-Holt form by 15 standard deviations (thus excluding local hidden-variable theories) and a violation of a Leggett-type non-local hidden-variable inequality by 3 standard deviations (thus excluding a certain class of non-local hidden-variable theories.)

AUTHOR INFORMATION

**Name:** Matthew D. Eisaman, **Division:** 844.03, **Lab:**
Physics, **Building / Room:** 221 / B212, **Mailstop: **8441,

**Phone: **301-975-8419, **Fax: **301-869-5700 , **Email:** matthew.eisaman@nist.gov, **Sigma Xi Member:** Yes,

**Mentor:** Alan Migdall (221/A213, x2331, alan.migdall@nist.gov), **Poster category:** Physics