Yusuf Turek

We introduce a programmable optical parametric amplifier (OPA) synthesizer that, under a heralded photon-number-resolving framework, generates high-fidelity cubic phase states (CPSs) and amplifies Schrödinger cat states. By systematically exploring both the catalytic configuration, where the idler input and output contain the same number of photons ( m = n ), and non-catalytic configurations ( m ≠ n ), we discover two qualitatively different functionalities. First, with a coherent-state signal input, our protocol generates CPSs with fidelity exceeding 0.99 across a broad range of ( m , n ) configurations. Second, using a Schrödinger cat state as the signal input, the same framework amplifies the cat state: an input cat with amplitude α in ⩽ 1 is transformed into an output squeezed cat with α out ⩾ 2 while maintaining fidelity above 0.99 . The catalytic configuration preserves the input parity and restores the idler state, whereas non-catalytic configurations enable parity-flipping amplification with higher success rates. Moreover, the amplified output can serve as a seed for subsequent amplification rounds, offering a self-seeding pathway to progressively larger cat states. Our protocol requires only moderate-gain OPA operation and low-order photon-number-resolving detection, providing a flexible and experimentally accessible platform for CPS preparation and amplified squeezed cat state generation.

The practical value of non-Gaussian states for quantum computation, metrology, and networking is currently limited by the intrinsically low success rates of conventional generation methods like photon addition and subtraction. We introduce a scalable protocol that overcomes this bottleneck using postselected von Neumann measurements beyond the weak-coupling regime. Applied to standard Gaussian inputs, our method efficiently generates a suite of critical resources—including large-amplitude Schrödinger cat states, Gottesman–Kitaev–Preskill-like states, and two-mode entangled states—with considerably higher success probabilities. Quantitative analysis of Wigner negativity and entanglement confirms their high quality. This work establishes postselected von Neumann measurement as a general and scalable principle for quantum resource generation, moving beyond a fundamental limitation in quantum state engineering.

The question of when the Kirkwood-Dirac quasiprobability serves as the most appropriate description for quantum measurements has remained unresolved, particularly across different measurement strengths. While known to generate anomalous weak values in the weak measurement regime and to reduce to classical probabilities under projective measurement, the physical mechanism governing its continuous transformation has been lacking. Here we demonstrate that the KD quasiprobability provides a general framework for all measurement regimes by identifying pointer-induced decoherence as the universal mechanism controlling this transition. We show that the decoherence factor F(t) simultaneously quantifies the loss of quantum coherence and interpolates the measurement strength from weak to strong. Within this framework, the KD quasiprobability naturally deforms from its full complex form-governing weak values-to the real, non-negative Wigner formula describing projective measurements, while maintaining informational completeness throughout the transition. Our work resolves the fundamental question of the KD distribution's applicability by establishing it as the universal framework that seamlessly connects all quantum measurement regimes through a physically transparent decoherence pathway.