Tuning Wave-Particle Duality of Quantum Light by Generalized Photon Subtraction

Abstract

Wave--particle duality is a hallmark of quantum mechanics. For bosonic systems, there exists a continuum of intermediate states bridging wave-like Schrödinger cat states and particle-like Fock states. Such states have recently been recognized as valuable resources for enhancing fault-tolerant quantum computation (FTQC) with propagating light. Here we experimentally demonstrate tunable generation of these intermediate states by employing generalized photon subtraction (GPS). By detecting up to three photons from squeezed-light sources with a photon-number-resolving detector, we continuously control the balance between wave- and particle-like features. This approach allows us to construct a spectral family of quantum states with high generation rates, optimized according to the required fault-tolerance threshold. Our results establish GPS as a versatile toolbox for tailoring non-Gaussian resources, opening a pathway to efficient Gottesman--Kitaev--Preskill (GKP) qubit generation and addressing a central bottleneck in optical quantum computing.

Figures (3)

• Figure 1: Simulation and applications of generalized photon subtraction (GPS). (a) Phase-resolved quadrature marginal distributions, showing the continuous transition from wave-like (phase-sensitive), through intermediate, to particle-like (phase-insensitive) states. (b) Conceptual overview of the role of GPS in optical quantum computing: a tunable state generator based on GPS produces intermediate states that serve as inputs for a breeding protocol, yielding logical (GKP) states for an optical FTQC takase2024.
• Figure 2: Experimental setup. Two broadband squeezed-vacuum sources (OPAs) are interfered with on a variable beam splitter (PBS--HWP--PBS). Conditional detection of up to three photons with SNSPDs, after spectral filtering with the bandwidth of 15MHz, heralds intermediate non-Gaussian states, which are then characterized by homodyne detection (HD).
• Figure 3: Reconstructed quantum states generated by GPS. Top row (a - c): Wigner functions of representative cases---(a) Fock-like state ($s_0=0.11, R=50\%$), (b) intermediate state ($s_0=0.5, R=40\%$), and (c) cat-like state ($s_0=1.2, R=30\%$). All states exhibit negativity, confirming their strong nonclassicality. Bottom row (d - f): Phase-resolved quadrature marginal distributions $p(x;\theta)$. The cat-like and intermediate states display phase-dependent oscillatory features, while the Fock-like state remains nearly phase-insensitive, illustrating the tunable transition from wave- to particle-like behavior, respectively.