# Can future observation of the living partner influence the past decayed state in entangled neutral K-mesons?

Jose Bernabeu, Antonio Di Domenico

Received Date: 20th February 20

The Einstein-Podolsky-Rosen (EPR) entanglement of a neutral K-meson (kaon) pair enjoys the peculiar quantum behaviour of mixing, charge-parity ${\cal CP}$ violation (${\cal C}$ - charge conjugation, ${\cal P}$ - parity) and two non-orthogonal eigenstates of definite time evolution $K_L$ and $K_S$ with very different lifetimes. The dynamics of this strange entanglement', experimentally accessible at the $\phi$-factory, makes possible the search for novel phenomena not accessible in any other system, i.e. at interference times and at decoherence times of the single partners after their disentanglement, in order to unveil the nature of the correlation between the two neutral kaons. Until now, the studies have been concentrated on the single kaon intensity distribution between the two decay times $t_1$ and $t_2$ with $\Delta t = t_2 - t_1 > 0$. Here we show that the entire two single time distributions, before each decay, are physical in both senses: "from past to future", leading to the state of the living partner at time $t_2$ from the observation of the first decay channel at $t_1$, and "from future to past", leading to the past state of the decayed kaon at time $t_1$ from the observation of the second decay channel at $t_2$. Our results thus demonstrate an affirmative answer to the title: it does, the past decayed state depends on the result of the future measurement for the living partner. This novel effect is truly observable through the first decay time distributions. Besides the implications for quantum physics for all $\Delta t$, at large decoherence times the resulting first decayed state is always $K_S$, providing a genuine tag of this kaon state in the decoherence region, and a unique and important experimental tool to prepare a pure $K_S$ beam.

Read in full at arXiv.

This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

### Nature Communications

Nature Research, Springer Nature