Scalable Entangled-Photon based Optical Quantum Computers

Project Information

sepoqc

Grant agreement ID: 190188855

DOI

10.3030/190188855

Project closed

EC signature date 19 December 2022

Start date 1 January 2023

End date 31 December 2024

Funded under

• The European Innovation Council (EIC)

Total cost

€ 3 570 000,00

EU contribution

€ 2 499 000,00

Coordinated by

QUANDELA
France

Periodic Reporting for period 2 - sepoqc (Scalable Entangled-Photon based Optical Quantum Computers)

Reporting period: 2024-01-01 to 2024-12-31

Summary of the context and overall objectives of the project

Quantum computers are one of the most promising technologies of the future, such devices should be capable of solving problems that are impossible even for the most powerful super computers nowadays. At Quandela, we chose to take this challenge using photons. In fact, photons, being chargeless and massless, are the ideal qubit materials since they are the only elementary particles with no decoherence, thus minimizing the loss of information. Based on over 25 years of research at the Center for Nanoscience and Nanotechnology, we demonstrated the world's first efficient emission of single photons powered by our unique semiconductor-based technology (Nature Photonics, 2016). In just a few years, we completed the design and construction of PROMETHEUS which is the first standalone and easy to use single photon source.
Based on this unique technology, we released MOSAIQ, the first full-stack photonic quantum computing platform in the world. MOSAIQ is designed and built to be modular, reconfigurable, interconnected and therefore scalable. It integrates state-of-the-art technologies such as PROMETHEUS, programmable photonic integrated circuits, efficient read-out devices and the associated operating system plus the software stack, such as PERCEVAL, an open-source framework to control and simulate hardware and algorithm layer.
The main objectives are:
- Improve the performances (brightness, purity, reproducibility) of the single photon sources in order to bring optical quantum computers into an unexplored regime, with near-deterministic flow of single and linearly entangled photons. Homogeneity of the semiconductor wafers will be improved in order to increase the fabrication volumes with a high reproducibility.
- Develop a new generation of opto-electronic modules that are at the core of our quantum computing platform for the efficient routing and manipulation of photons. The objective is to increase the number of quantum bits to several dozen by minimizing the optical losses, improving the speed of active elements and ensuring a high stability of the whole system.
- Develop a library of quantum algorithms and the next generation of software simulating and controlling Quandela quantum computer.
- Prepare the commercialization of quantum computers by creating market segmentation analysis to identify key customer groups and needed product feature.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

• During the first part of the project, we focused on the improvement of the fibered brightness of single photon sources and we enhanced the average brightness by a factor 2.
In parallel, we successfully demonstrated control over the spin of QDs for spin-photon and spin mediated photon-photon entanglement and. The preliminary results on wafer growth homogeneity pave the way to fabricate identical single-photon sources at scale as resources for a large optical quantum computer.
• We fabricated two proof-of-concept prototypes of an active demultiplexer system using fast electro-optics deflectors. We have designed optical systems, developed the electronic driver used to reach high speed and high amplitude deflection. With the first one, the resonant modulation demultiplexer, we have demonstrated the separation of one optical beam into 8 outputs with a high optical transmission. With the second prototype, we have demonstrated the routing of two pulses within 20 ns, with 98.5% separation efficiency.
• To achieve a robust and scalable simulation of photonic processors, the work was concentrated on extending the capability of linear optics simulation with the following goals:
- Assist hardware development by modeling noise and imperfections and comparing output of the simulator with hardware to simultaneously identify possible improvement in the models and possible flaws in the hardware implementation
- Assist development of quantum algorithms by providing realistic simulation capability beyond the capacity of current generation of hardware and providing support for development of a hybrid system,
- Go beyond physical observable features, provide quantum state manipulation and analysis features for development of theory.

• We have introduced a modular hybrid architecture designed for fault-tolerant quantum computing. This architecture fully exploits the main advantages of photons by exploiting the modularity and the connectivity through optical links.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We improved the quality of fabrication of sources in order to reach a greater brightness from pigtailed sources at the end of a single mode fiber. We have demonstrated the doubling of the fiber brightness from 9% to 18% while maintaining a high photon indistinguishability (greater than 95%) and high single-photon purity (greater than 98%).
By combining high fiber brightness, high single photon purity and high photon indistinguishability, the pigtailed sources represent the state-of-the-art as a quantum light emitter.

In 2023, Quandela received a first order of its quantum computing platform, MOSAIQ. It integrates PROMETHEUS including one bright pigtailed source. The source was integrated in the same cryostat chamber with efficient SNSPD detectors. Therefore, we demonstrated the feasibility and reliability of building compact and efficient, all-in-one platform dedicated to quantum computing which is compatible with data-center environment.
To our knowledge, this is the first demonstration of installation of a photonic quantum computer in an industrial datacenter.

In parallel, we maintained the operation of our first quantum computer in the cloud, Ascella. An availability of more than 90% has been demonstrated, proving the stability of the photonic platform.

During 2023, we also released many upgrades of Perceval, an open-source framework developed by Quandela.

We have introduced a novel encoding scheme in process to being patented enabling to reduce the use of probabilistic gates when compiling a gate-based circuit into a photonic circuit.
We have introduced a new method to compile a given unitary on a physical photonic chip allowing to increase fidelity of the implemented circuit represented by its unitary – this work is in the process of being published.

Additional work on the compilation of algorithm for Measurement Based Quantum Computer (MBQC) framework is in progress to implement a MBQC compilation through ZX calculus, as well as a simulator for graph state is being developed for Perceval.

This compilation process will define conversion protocol between quantum algorithms and a sequence of transformation and measurement on a photonic graph state with the possibility to take into account error mitigation.