An entanglement analogue in light cones

The four-vector formalism is commonly used in Minkowski spacetime, but there exists an alternative formalism with spinors. We revisit the spinor formalism in the context of quantum information and establish an unexpected connection between directions in light cones and the notion of entanglement. This allows us to interpret that timelike directions correspond to entangled states of two imaginary qubits, whereas null directions correspond to separable states. With the correspondence, the speed of a particle can be expressed in terms of the amount of entanglement in concurrence. Furthermore, the entanglement also leads to a novel interpretation of the fact that moving clocks run slowly.