Causal Architecture in Hidden Quantum Markov Models
This paper introduces causal hidden quantum Markov models (cHQMMs) where emissions precede hidden state transitions, demonstrating that this causal order generally produces distinct, distinguishable quantum processes compared to conventional models, while proving that the two architectures converge only when derived from entangled liftings of classical hidden Markov models, thereby establishing a clear boundary between classical and genuine quantum memory effects.