Periodic Reporting for period 1 - CLUSTEC (Scalable Continuous Variable Cluster State Quantum Technologies)
Periodo di rendicontazione: 2022-11-01 al 2024-04-30
CLUSTEC is a pioneering EU Horizon Europe initiative aimed at unlocking the potential of optical cluster states for scalable quantum technologies. Despite rapid advancements in quantum computing, scalability remains a key challenge. CLUSTEC addresses this by leveraging continuous variable (CV) cluster state technology to build a universal, fault-tolerant, and network-compatible quantum computer. The project seeks to answer fundamental questions related to scalability, computational universality, quantum error-correction, and quantum advantage certification.
The initiative brings together the expertise of eight international partners from Germany, France, Switzerland, the Czech Republic, and Denmark, uniting leading researchers and industry partners in quantum technology, photonic integration, mathematics, computer science, and quantum information theory. CLUSTEC aims to demonstrate critical steps towards CV quantum computing and quantum networking. To achieve this, CLUSTEC has set four primary objectives:
(i) Developing experimental platforms for CV cluster state generation based on fiber optics and the lithium niobate on insulator platform.
(ii) Exploring CV cluster states of different network topologies to understand the role of entanglement structures in practical quantum technologies.
(iii) Developing and executing quantum protocols and near-term quantum algorithms with certified quantum advantage using CV cluster states.
(iv) Exploring new quantum error correction schemes towards fault-tolerant CV cluster state quantum computing and networking.
The project's outcomes are expected to significantly advance quantum computing by overcoming current limitations and providing a clear pathway towards scalable, fault-tolerant quantum technologies. By addressing these critical challenges, CLUSTEC aims to pave the way for the next generation of quantum computing and networking, with substantial impacts on the quantum technology landscape and society at large.
The initiative brings together the expertise of eight international partners from Germany, France, Switzerland, the Czech Republic, and Denmark, uniting leading researchers and industry partners in quantum technology, photonic integration, mathematics, computer science, and quantum information theory. CLUSTEC aims to demonstrate critical steps towards CV quantum computing and quantum networking. To achieve this, CLUSTEC has set four primary objectives:
(i) Developing experimental platforms for CV cluster state generation based on fiber optics and the lithium niobate on insulator platform.
(ii) Exploring CV cluster states of different network topologies to understand the role of entanglement structures in practical quantum technologies.
(iii) Developing and executing quantum protocols and near-term quantum algorithms with certified quantum advantage using CV cluster states.
(iv) Exploring new quantum error correction schemes towards fault-tolerant CV cluster state quantum computing and networking.
The project's outcomes are expected to significantly advance quantum computing by overcoming current limitations and providing a clear pathway towards scalable, fault-tolerant quantum technologies. By addressing these critical challenges, CLUSTEC aims to pave the way for the next generation of quantum computing and networking, with substantial impacts on the quantum technology landscape and society at large.
The project made significant progress toward fulfilling the four primary project objectives, resulting in 18 published manuscripts (6 preprints). Notably, developments in Work Packages 3 and 4 have resulted in the following accomplishments: We have successfully fabricated a ring resonator designed to generate squeezed light through modal phase matching. To date, we have achieved a squeezing measurement of -0.5 dB. To improve the squeezing measurement, we developed both 3D couplers and grating couplers for fiber-to-chip coupling. The 3D couplers exhibited a coupling loss of -1.4 dB/facet. For the grating couplers, we achieved a coupling loss of -2.2 dB/coupler without a metal back reflector and -1.4 dB/coupler with a metal back reflector. Results on the fiber-to-chip coupling are summarized in Deliverable D4.1. Currently, we are investigating the feasibility of generating two squeezed light outputs using a single ring resonator. The next phase of our research involves performing entanglement measurements using two squeezed light sources produced by a single ring resonator as the squeezing source. In addition, we established periodic poling for quasi-phase matching and first second harmonic generation measurements yield a normalized conversion efficiency of up to 2000%/Wcm². Translating the results into a ring resonator and testing the capabilities of the theoretically more suitable platform of MgO-doped lithium niobate is currently under process.
On the theoretical edge, activities in Work Package 2 and 5 have focused on exploring higher-dimensional cluster states beyond universal 2D lattices and potentially fault-tolerant 3D cluster states, including new 4D architecture, preparation of magic states and use of GKP states and systematic and rigorous identification of genuine multipartite Gaussian entanglement up to 16 parts. Additionally, the work included a systematic study on different linear-optical topologies with the realistic input Gaussian squeezed states up to 500 to reliably build the cluster states and other related applications. The work has resulted in several new proposals including: (i) generation of cluster states, rotation invariant codes and more general graph states when the nodes are GKP qubits solely employing passive linear optics with an initial supply of single-mode GKP states, (ii) autonomously generating quantum non-Gaussian states with a negative Wigner function, (iii) a new certification scheme for CV graph states as the universal resource for quantum information and computation, (iv) algorithms to perform efficient quantum simulations of symmetry-breaking nonlinear interaction based on a collision approach suitable for many experimental platforms. Activities in Work Package 5 have contributed towards Objective 3 by developing a new quantum algorithm for Gaussian Boson Samplers, which in a broad range of cases, can provide exponential speed up over Monte Carlo simulation. In addition, various applications of the new GBS algorithm have been explored, such as computing prices of various financial instruments, computing marginal distribution/likelihood in statistical machine learning and in general stochastic optimization.
On the theoretical edge, activities in Work Package 2 and 5 have focused on exploring higher-dimensional cluster states beyond universal 2D lattices and potentially fault-tolerant 3D cluster states, including new 4D architecture, preparation of magic states and use of GKP states and systematic and rigorous identification of genuine multipartite Gaussian entanglement up to 16 parts. Additionally, the work included a systematic study on different linear-optical topologies with the realistic input Gaussian squeezed states up to 500 to reliably build the cluster states and other related applications. The work has resulted in several new proposals including: (i) generation of cluster states, rotation invariant codes and more general graph states when the nodes are GKP qubits solely employing passive linear optics with an initial supply of single-mode GKP states, (ii) autonomously generating quantum non-Gaussian states with a negative Wigner function, (iii) a new certification scheme for CV graph states as the universal resource for quantum information and computation, (iv) algorithms to perform efficient quantum simulations of symmetry-breaking nonlinear interaction based on a collision approach suitable for many experimental platforms. Activities in Work Package 5 have contributed towards Objective 3 by developing a new quantum algorithm for Gaussian Boson Samplers, which in a broad range of cases, can provide exponential speed up over Monte Carlo simulation. In addition, various applications of the new GBS algorithm have been explored, such as computing prices of various financial instruments, computing marginal distribution/likelihood in statistical machine learning and in general stochastic optimization.
The project progressed beyond state of the art by enhancing the technical capabilities of the experimental setup and advancing numerous theoretical aspects. These key results have been disseminated through 18 published manuscripts, including 6 preprints. Several highlights are summarized under "work performed and main achievements".