Experimental Proof of Nonlocal Wavefunction Collapse for a Single Particle Using Homodyne Measurement

TL;DR

This experiment demonstrates nonlocal wavefunction collapse for a single photon by violating an EPR-steering inequality, confirming Einstein's spooky action at a distance without loopholes.

Contribution

First experimental demonstration of nonlocal wavefunction collapse for a single particle using homodyne measurements and EPR-steering inequality violation.

Findings

Violates EPR-steering inequality by 0.042 ± 0.006

Verifies entanglement of split single photon even with untrusted side

Confirms nonlocal wavefunction collapse without efficiency loopholes

Abstract

A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances, but it is never detected in two (or more) places. This strange phenomenon is explained in quantum theory by what Einstein repudiated as "spooky action at a distance": the instantaneous nonlocal collapse of the wavefunction to wherever the particle is detected. We demonstrate this single-particle spooky action, for the first time with no efficiency loophole, by splitting a single photon between two laboratories and experimentally testing if the choice of measurement in one lab really causes a change in the local quantum state in the other lab. To this end, we use homodyne measurements with six different measurement settings and quantitatively verify Einstein's spooky action by violating an Einstein-Podolsky-Rosen-steering inequality by $0.042 \pm 0.006$. Our experiment also verifies the entanglement of the split single photon even when one side is untrusted.