Quantum vampire: collapse-free action at a distance by the photon annihilation operator

TL;DR

This paper demonstrates a nonlocal quantum action-at-a-distance where applying a photon annihilation operator to one part of an entangled light state removes a photon from the entire state without local collapse, challenging classical intuitions.

Contribution

It introduces a method to remove a photon from a distributed quantum state nonlocally without collapsing the local state, revealing new aspects of quantum nonlocality.

Findings

Photon subtraction affects the entire mode nonlocally

Homodyne tomography confirms mode jumps to lower Fock state

No shadow observed when applying annihilation operator to part of the mode

Abstract

A nonclassical state of light is distributed, via a beam splitter, between two remote parties. One of the parties applies the photon annihilation operator to its portion of the state. Surprisingly, this local intervention removes a photon from the entire initial state, leaving its mode as well as the spatial and temporal structure undisturbed. In this way, nonlocal quantum action-at-a-distance occurs without local state collapse by either party. This leads to curious consequences, such as the absence of a shadow when the annihilation operator is applied to a part of the spatial cross-section of the initial optical mode. In the experiment, we subtract a single photon from a part of an optical mode initially prepared in the one- or two-photon Fock state. Subsequent homodyne tomography reveals that the whole mode has jumped to the next lower Fock state, with no change in the mode shape.