Superposition Trap: An Interferometric Mechanism to Monitor Quantum State Collapse in Real Time

The measurement problem in quantum mechanics raises the question of whether wavefunction collapse is a physical dynamical process or an effective description arising from environmental decoherence. Experimental access to collapse dynamics is challenging, since direct measurement of a quantum system typically induces collapse itself.

We present an experimental concept—the superposition trap—that circumvents this difficulty by spatially confining only coherent superposition states, while allowing decohered or collapsed components to escape and be detected. The mechanism exploits the continuity equation of quantum mechanics: destructive interference is engineered at the boundaries of a trapping geometry, producing nodal surfaces with vanishing probability current. As long as coherence is preserved, the wavefunction remains trapped; loss of coherence lifts the destructive interference, resulting in leakage from the trap.

The escaped population provides a non-invasive, real-time signal of collapse or decoherence events, without requiring direct measurement of the trapped coherent state. We outline optical and atom-interferometric realizations of the superposition trap, with particular emphasis on an implementation using strontium atom interferometry and internal-state-selective removal of decohered atoms.

The superposition trap offers a new experimental handle on quantum state reduction, enabling controlled studies of decoherence dynamics and providing a potential platform for testing objective collapse models. Beyond foundations, this mechanism may also find applications in quantum control and error filtering, where preserving coherence is essential.