Demonstration that Einstein-Podolsky-Rosen steering requires more than one bit of faster-than-light information transmission

TL;DR

This paper demonstrates that Einstein-Podolsky-Rosen steering requires transmitting more than one bit of information faster than light, challenging local hidden state explanations and supporting nonlocal quantum effects.

Contribution

It introduces loss-tolerant EPR-steering inequalities with multiple measurement settings and shows experimental violation with only one bit of classical communication, closing key loopholes.

Findings

Violation observed with 3 measurement settings and 2-bit classical message

Experiment closes efficiency and locality loopholes

More than one bit of FTL information transmission is required

Abstract

Schr\"odinger held that a local quantum system has some objectively real quantum state and no other (hidden) properties. He therefore took the Einstein-Podolsky-Rosen (EPR) phenomenon, which he generalized and called `steering', to require nonlocal wavefunction collapse. Because this would entail faster-than-light (FTL) information transmission, he doubted that it would be seen experimentally. Here we report a demonstration of EPR steering with entangled photon pairs that puts--in Schr\"odinger's interpretation--a non-zero lower bound on the amount of FTL information transmission. We develop a family of $n$-setting loss-tolerant EPR-steering inequalities allowing for a size-$d$ classical message sent from Alice's laboratory to Bob's. For the case $n=3$ and $d=2$ (one bit) we observe a statistically significant violation. Our experiment closes the efficiency and locality loopholes, and we address the freedom-of-choice loophole by using quantum random number generators to independently choose Alice's and Bob's measurement basis settings. To close the efficiency and locality loopholes simultaneously, we introduce methods for quickly switching between three mutually unbiased measurement bases and for accurately characterizing the efficiency of detectors. From the space-time arrangement of our experiment, we can conclude that if the mechanism for the observed bipartite correlations is that Alice's measurement induces wave-function collapse of Bob's particle, then more than one bit of information must travel from Alice to Bob at more than three times the speed of light.