QI
In the literature: open
Bell test for temporal order using a mass in superposition
In plain words
If a heavy mass is in a superposition of two positions, nearby clocks tick at superposed rates, which can put the order of two events in superposition. A proposed Bell-type test would show this order is not fixed in advance by hidden variables.
Precise statement
Zych, Costa, Pikovski and Brukner (Nature Communications 2019) proposed a Bell-type inequality for the temporal order of events controlled by a massive body in spatial superposition. Using the weak-field proper-time difference $\Delta \tau \sim G M \Delta x t / (c^{2} d^{2})$, determine the minimal mass, separation and coherence time for a violation, and demonstrate it.
What would settle it
Observation of the predicted violation with a source mass in spatial superposition.
See also
- Related Observe entanglement created only by gravity between two masses
- Related Can causal inequalities be violated when spacetime itself is superposed?
- Related Measure quantum time dilation of a clock in a momentum superposition
- Related Do laboratory quantum switches realize genuinely indefinite causal order?