Unitary-accessible coherence-erasure distance: Exact qubit solution and a tight qutrit bound
The unitary-accessible coherence-erasure distance measures the minimum unitary control cost to turn a quantum state into an incoherent state while keeping its spectrum unchanged. For qubits, this distance depends on eigenbasis orientation, not eigenvalues. For qutrits, a tight universal bound was found. This new measure provides an operational meaning for coherence erasure under physical unitary driving.