Generating GKP states using quantum dots inside a strongly coupled cavity

Research Context and Motivation

Continuous-variable (CV) quantum information processing requires non-Gaussian resource states to achieve universal quantum computation and fault tolerance. The Gottesman-Kitaev-Preskill (GKP) state is a primary candidate for this, as it encodes logical qubits into periodic grid structures in phase space. While ideal GKP states are unphysical due to their infinite energy, finite-energy approximations—specifically the qunaught state—are essential for practical architectures. Current optical methods for generating these states often suffer from low success probabilities, motivating the search for more efficient, scalable generation protocols.

The Proposed Protocol

This paper introduces a hybrid approach that leverages the deterministic nature of cavity quantum electrodynamics (QED). The protocol consists of three main stages:

1. Deterministic Cat-State Generation: A quantum dot embedded in a strongly coupled optical cavity is used to generate squeezed Schrödinger cat states via spin-dependent reflection of optical pulses.
2. Cat-Breeding: These cat states are processed through a multi-round breeding protocol, where interference on a beam splitter and subsequent homodyne measurements convert them into grid-like structures.
3. Relaxed Post-Selection: Instead of strictly post-selecting on a single homodyne measurement outcome, the authors utilize a structured set of outcomes. This significantly increases the overall success probability of the state generation while maintaining high fidelity.

The proposed scheme bridges the gap between high-quality bosonic encodings and industry-relevant quantum technologies. By utilizing quantum dot-cavity systems, the protocol is compatible with telecom wavelengths and integrated photonics, offering a path toward scalable, room-temperature-compatible quantum networks. The numerical analysis provided in the paper demonstrates that this approach can achieve higher success rates than existing bulk-optical or photon-subtraction-based methods, providing a concrete roadmap for experimental implementation.