Quantum Pulse Scattering Theory



Single-Photon Detection Using Quantum Phase Transitions

We propose a single-photon detector by exploiting the universal first-order quantum phase transition (QPT) in interacting spin systems. We utilize a time-dependent theoretical framework to study the absorption of a single photon pulse by an engineered defect (i.e., a nitrogen-vacancy center) which nucleates the single shot quantum measurement. This concept of a single-shot detection event (“click”) is different from parameter estimation which requires repeated measurements. The crucial step of amplifying the weak quantum signal occurs by coupling the defect to a system of interacting spins biased close to a QPT point. The macroscopic spin-order change during the QPT generates an amplified signal, which can be read out by a classical device. Our amplification scheme is based on the giant sensitivity of the first-order QPT, which fundamentally originates from the diverging higher-order spin-spin correlation at the phase transition point.


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