Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

A strong loophole-free test of local realism



Lynden K. Shalm, Evan Meyer-Scott, B. G. Christensen, Peter L. Bierhorst, Michael A. Wayne, Deny Hamel, Martin J. Stevens, Thomas Gerrits, Scott C. Glancy, Michael S. Allman, Kevin J. Coakley, Shellee D. Dyer, Adriana E. Lita, Varun B. Verma, Joshua C. Bienfang, Alan L. Migdall, Yanbao Zhang, William Farr, Francesco Marsili, Matthew D. Shaw, Jeffrey Stern, Carlos Abellan, Waldimar Amaya, Valerio Pruneri, Thomas Jennewein, Morgan Mitchell, P. G. Kwiat, Richard P. Mirin, Emanuel H. Knill, Sae Woo Nam


We present a loophole-free violation of local realism using entangled photon pairs. We ensure that all relevant events in our Bell test are spacelike separated by placing the parties far enough apart and by using fast random number generators and high-speed polarization measurements. A high-quality polarizationentangled source of photons, combined with high- efficiency, low-noise, single-photon detectors, allows us to make measurements without requiring any fair-sampling assumptions. Using a hypothesis test, we compute p values as small as 5.9 x 10−9 for our Bell violation while maintaining the spacelike separation of our events. We estimate the degree to which a local realistic system could predict our measurement choices. Accounting for this predictability, our smallest adjusted p value is 2.3 x 10−7. We therefore reject the hypothesis that local realism governs our experiment.
Physical Review Letters


Bell inequality, local realism, entanglement


Shalm, L. , Meyer-Scott, E. , Christensen, B. , Bierhorst, P. , Wayne, M. , Hamel, D. , Stevens, M. , Gerrits, T. , Glancy, S. , Allman, M. , Coakley, K. , Dyer, S. , Lita, A. , Verma, V. , Bienfang, J. , Migdall, A. , Zhang, Y. , Farr, W. , Marsili, F. , Shaw, M. , Stern, J. , Abellan, C. , Amaya, W. , Pruneri, V. , Jennewein, T. , Mitchell, M. , Kwiat, P. , Mirin, R. , Knill, E. and , S. (2015), A strong loophole-free test of local realism, Physical Review Letters, [online], (Accessed May 9, 2021)
Created December 16, 2015, Updated November 10, 2018