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arXiv:2608.10604

Generating GKP states using quantum dots inside a strongly coupled cavity

Viswatma Kamath, Ravi Mehta, Biman Chattopadhyay, Sandeep K Goyal

quant-phSubmitted Aug 11, 2026• Announced Aug 12, 2026• 0 citations
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Abstract

GKP states enable fault-tolerant CV quantum computation, but their generation remains experimentally challenging due to their highly non-Gaussian and infinite-energy ideal structure. In this work, we present a realistic and scalable protocol for generating finite-energy resource states, specifically the qunaught state, using Schrodinger cat states generated in a strongly coupled quantum dot-cavity system. Our scheme combines deterministic squeezed cat-state generation, cat-breeding protocols, and homodyne measurements. Using numerical simulations, we analyze the role of various parameters of the quantum dot-cavity system in the generation of practical qunaught states. Furthermore, we quantify the trade-off between the fidelity and generation probability of these states and exploit the fact that accepting a structured set of homodyne outcomes can significantly enhance the overall success rate. The proposed approach is compatible with integrated photonics and telecom wavelengths, offering a promising route toward scalable CV quantum information processing.

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GKP states enable fault-tolerant CV quantum computation, but their generation remains experimentally challenging due to their highly non-Gaussian and infinite-energy ideal structure. In this work, we present a realistic and scalable protocol for generating finite-energy resource states, specifically the qunaught state, using Schrodinger cat states generated in a strongly coupled quantum dot-cavity system. Our scheme combines deterministic squeezed cat-state generation, cat-breeding protocols, and homodyne measurements. Using numerical simulations, we analyze the role of various parameters of the quantum dot-cavity system in the generation of practical qunaught states. Furthermore, we quantify the trade-off between the fidelity and generation probability of these states and exploit the fact that accepting a structured set of homodyne outcomes can significantly enhance the overall success rate. The proposed approach is compatible with integrated photonics and telecom wavelengths, offering a promising route toward scalable CV quantum information processing.
Hybrid bosonic codes combining bosonic codes with photon states offer a promising pathway for fault-tolerant quantum computation. However, the efficient generation of such states in optical setups remains technically challenging due to the requirement for complex non-Gaussian resources. In this paper, we propose a novel scheme to efficiently generate hybrid entangled states between a GKP qubit and a photon-number state using small-amplitude cat states as the primary resource. We apply a breeding process using small-amplitude cat states to increase the non-Gaussianity of the input states. This method requires only linear optical elements and homodyne measurements. Furthermore, we demonstrate that this protocol can be extended to generate hybrid qudit states. This scheme has the potential to provide a resource-efficient and experimentally attractive route toward implementing hybrid quantum error correction.
Gottesman-Kitaev-Preskill (GKP) states are a central resource for fault-tolerant optical continuous-variable quantum computing and communication. However, their realization in the optical domain remains to be demonstrated. Here we propose a method for preparing GKP states using a cavity QED system as the only non-Gaussian element. This system can be realized in several platforms such as trapped atoms, quantum dots or diamond color centers. We simulate the protocol with finite-cooperativity systems to evaluate the achievable quality of the produced GKP states in realistic noisy systems. We further combine the protocol with the previously proposed breeding protocol by Vasconcelos et al. to relax the demands on the quality of the QED system. We find that GKP states with more than 10 dB squeezing could be achieved in near-future experiments. Additionally, the approach can be made fully deterministic, thus providing a more scalable and hardware-efficient approach compared to probabilistic approaches based on photon counting.
Optical system is an appealing system for quantum computation as it has tremendous scalability over typical matter-based qubit. This is thanks to its rich degree of freedom that allows multiplexing. A particularly promising approach is the time-domain multiplexing approach where large-scale entangled resources and their usages have been demonstrated. To achieve quantum computation, these resources have to be combined with a type of states called non-Gaussian states. Non-Gaussian state generation requires strong nonlinearity which is challenging in optical system, compared to the matter-based system. In this work, we explain our recent work in the generation of the non-Gaussian states for optical quantum computer. In the first half, we discuss the demonstration of cat-breeding protocol for the generation of Gottesman-Kitaev-Preskill (GKP) qubit. In the second half, we show the demonstration of generation of cat states from broadband light source. In the future, by combining these two techniques, we can achieve high-rate high-quality GKP states crucial for optical quantum computer.
The generation of non-Gaussian quantum states is a key requirement for universal continuous-variable quantum information processing. We report the experimental generation of large-amplitude squeezed coherent-state superpositions (squeezed cat states) on free-space optical pulses, reaching an amplitude of α=2.47α= 2.47α=2.47, which, to our knowledge, exceeds all previously reported values. Our protocol relies on the controlled mixing of the Fock states ∣1⟩|1\rangle∣1⟩ and ∣2⟩|2\rangle∣2⟩ through a tunable beam splitter, followed by heralding via homodyne detection. The resulting state displays three well-resolved negative regions in its Wigner function and achieves a fidelity of 0.530.530.53 with the target state ∝S^(z)(∣α⟩−∣−α⟩)\propto \hat{S}(z)(|α\rangle - |-α\rangle)∝S^(z)(∣α⟩−∣−α⟩), with α=2.47α= 2.47α=2.47 and squeezing parameter z=0.56z = 0.56z=0.56. These results constitute a significant milestone for temporal breeding protocols and for the iterative generation of optical GKP states, opening new perspectives for scalable and fault-tolerant photonic quantum architectures.
Non-Gaussian states of light, such as Gottesman-Kitaev-Preskill states, are essential resources for optical continuous-variable quantum computing. The ability to efficiently produce these states would open up tremendous prospects for quantum technologies in general and fault-tolerant quantum computing in particular. This letter demonstrates a versatile method using a quantum-memory cavity to mitigate the consequences of the probabilistic nature of the breeding protocols and generate non-Gaussian states at high rates with scalability perspectives. The performances of our experimental setup are illustrated with the generation of squeezed cat states of amplitude α=1.63 with a fidelity of more than 60% at a generation rate in the kHz range, which is higher than the state of the art for such states.
We present an architecture for the generation of GKP states in which quadrature squeezing operations are used to control the average photon number statistics of probabilistic photon number measurements on Gaussian resource states. Specifically, we present an architecture employing a teleportation-based squeezing protocol and polynomial-gate applications integrated into a time-multiplexed multi-mode cluster state to generate cat states with high amplitudes, which are consequently used to generate GKP states with high quadrature effective squeezing. Compared to our previous work, in addition to using squeezing as a resource, the present architecture reduces damping and noise by minimizing the number of homodyne measurements required in GKP state generation. We demonstrate the effectiveness of these improvements - including dynamic input-state resetting and an improved breeding algorithm - by achieving a fault-tolerance threshold of 11.5 dB cluster squeezing using the RHG surface code for error correction, without requiring active switching or photon-number resource states.