The time qubit

TL;DR

This work reframes time as a quantum degree of freedom by introducing a time qubit that encodes forward versus backward evolution. It shows how a Mach-Zehnder interferometer with opposite magnetic fields realizes coherent superpositions of temporal orientations, producing time-parity interference and enabling Bell-type tests with a spin qubit. The Dirac equation is recast as a coupling between a spin qubit and a time qubit, with matter/antimatter corresponding to opposite temporal poles and zitterbewegung arising from time-qubit precession. Conceptually, this unifies interferometric, nonrelativistic, and relativistic aspects of temporal symmetry, and operationalizes temporal orientation as a quantum resource with potential metrological and foundational applications.

Abstract

A spin precessing in a magnetic field is often used as a quantum clock, for example in tunneling-time measurements. We show that such a clock can exist in a coherent superposition of opposite temporal orientations, treating the arrow of time as a quantum two-level system. A Mach-Zehnder interferometer with equal and opposite magnetic fields provides a simple implementation, enabling interference between forward and backward evolution and Bell-type tests of temporal coherence. Extending the framework to relativistic dynamics reveals that the Dirac Hamiltonian describes an intrinsic coupling between a spin qubit and a time qubit, with matter and antimatter corresponding to opposite poles on the temporal Bloch sphere.