Integrated Generation and Purification of Entangled Coherent States for Non-Gaussian Teleportation

Abstract

Entangled coherent states (ECS) provide a powerful non-Gaussian resource for continuous-variable quantum communication, but their generation in scalable architectures remains challenging. We propose an integrated photonic scheme that creates high-fidelity ECS from a two-mode squeezed vacuum via photon subtraction in a symmetric waveguide trimer. The resulting non-Gaussian entanglement is further enhanced by single-photon catalysis, which purifies the distributed state after transmission through lossy channels. Using these purified ECS resources, we analyze a photon-number-based teleportation protocol and demonstrate high-fidelity transfer of both coherent states and Schrodinger cat states. In particular, the teleportation fidelity for cat states exceeds the classical threshold of 2/3 over a broad range of realistic channel and squeezing parameters, whereas Gaussian resources fail to do so. Our results show that integrated photon subtraction and catalysis enable practical, chip-compatible generation of non-Gaussian entanglement suitable for advanced quantum teleportation and continuous-variable quantum networks.

Figures (8)

• Figure 1: (a) Schematic setup of the entanglement distribution protocol where a source located midway between Alice and Bob, separated by a distance $L$, emits an entangled state $\hat{\rho}$ that is shared between them. (b) Main building blocks of the protocol, including the trimer-based state-generation module, the purification stage, and the photon-number–based teleportation module.
• Figure 2: Average teleportation fidelity $F^{(\mathrm{cat})}_{\mathrm{TMSVS}}$ for teleporting a cat state using TMSVS as the entangled resource, plotted as a function of the channel loss $\eta$ and the squeezing amplitude $|r|$, for $\beta=0.55$.
• Figure 3: Average teleportation fidelity $F^{(\gamma)}_{\mathrm{ECS}}$ for teleporting a coherent state $\ket{\gamma}$ using unpurified quasi-ECS entangled resources as a function of the coherent-state amplitude $\gamma$ and the squeezing amplitude $|r|$, for $z = 1.25$, $N = 1$, and $\eta=1$. The black contour line corresponds to $F^{(\gamma)}_{\mathrm{ECS}} = 2/3$, which represents the classical fidelity limit for teleporting a qubit using a purely classical strategy.
• Figure 4: Fidelity of quasi-ECS showing the dependence on the propagation distance $z$ and squeezing amplitude $|r|$ for different values of the ECS amplitude $\alpha$ and number of subtracted photons $N$.
• Figure 5: Fidelity and purity of the quasi-ECS as functions of the channel loss $\eta$ and squeezing parameter $|r|$, for $z = 1.25$ and $N = 1$. The fidelity plots (top row) correspond to $\alpha = 0.5$: (a) before and (b) after purification using single-photon catalysis implemented via a directional coupler with transmission coefficient $T = 0.1$. The bottom row presents the corresponding purity (c) before and (d) after purification.