Quantum Simulation with Universal Nonlinear optics

Project Information

QSun

Grant agreement ID: 101063763

DOI

10.3030/101063763

Project closed

EC signature date 9 June 2022

Start date 1 October 2022

End date 30 June 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 230 774,40

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 1 - QSun (Quantum Simulation with Universal Nonlinear optics)

Reporting period: 2022-10-01 to 2025-06-30

Summary of the context and overall objectives of the project

Devices that exploit the laws of quantum physics provide fundamentally new opportunities and computational advantages with respect to conventional or classical hardware. By exploiting an inherently new way to encode and process information, quantum technologies promise multiple disruptive applications: enormous computational speed-ups via quantum computers and simulators, unconditionally secure communication networks, and quantum-enhanced sensors.

Amongst the leading quantum platforms, photons offer unique advantages as quantum information carriers: low noise, long-distance transmission, high-speed, and high manufacturability of quantum photonic circuits. Recent advances for near-term industrially relevant applications for photonic simulators, as well as resource-efficient fault-tolerant linear-optical quantum computing architectures, have opened exciting new prospects for photonic quantum technologies, spurring large investments in quantum photonic companies (e.g. PsiQuantum, Xanadu, Photonic Inc.). However, an important hurdle currently limits the scaling up of quantum photonic devices: the lack of near-deterministic nonlinearities in quantum photonic circuits for quantum simulators and scalable generation of multi-photon entanglement.

The aim of this project is to develop a technology to address this central limitation, nonlinear quantum photonics, enabling transformative quantum technologies for photonic quantum simulation, computing, and networking. In particular, the proposed project aims at addressing scientific gaps by introducing nonlinear quantum operations through light-matter interactions in quantum dots embedded in photonic nanostructures. These devices are then integrated in programmable linear-optical circuitry to build a scalable platform for developing multi-mode nonlinear quantum photonic. The action involves technology developments targeting applications in near-term devices, focusing on molecular quantum dynamics simulation, as well as progress towards hardware for longer-term general-purpose quantum computers. The goals represent significant scientific breakthroughs, outlined in the following key objectives:

(O1) Demonstration of universal nonlinear photonic circuits interconnecting nonlinear operations and programmable linear optics.
(O2) Implementation of anharmonic molecular dynamics quantum simulation in a programmable nonlinear interferometer.

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

The activities in “QSUN” have focused on three main aspects required to achieve its goals: 1) development of technologies for building complex nonlinear quantum photonic devices by interfacing photonic circuits with quantum emitters; 2) investigation of theoretical schemes for implementing scalable quantum computing and simulation applications with such technology; and 3) proof-of-principle demonstration of anharmonic molecular quantum dynamics through a programmable nonlinear photonic quantum simulator.

The project started by focusing on developing high-quality quantum emitters through InAs quantum dots embedded in GaAs photonic crystal waveguides, which represent the building block mediating the photon-photon nonlinearity, and interfacing them with programmable photonic circuits. The methods developed included investigating ways to reduce errors in such quantum emitters due to noises in the magnetic and electrical environments surrounding the solid-state quantum dots, tailoring control pulse sequences, and reducing optical losses in the system to improve photon counts.

Once these techniques were well established, I proceeded to experimentally test the building block for quantum photonic operations. In particular, I interfaced the quantum dot deterministic photon emitter with programmable integrated photonic circuits in two emerging platforms: Silicon Nitride (SiN) and Lithium Niobate on insulator (LNOI) chips. These materials were chosen due to their several advantages: they are compatible with the quantum dots' emission wavelengths, have extremely low loss, and are compatible with large-scale circuit integration. Furthermore, LNOI can integrate ultra-fast on-chip modulators enabling chip reprogramming at GHz speed. These were the first demonstrations of a solid-state quantum emitter interfaced with a SiN and LNOI integrated circuits.

By using the photonics circuits described above and additional fiber-based operations, I proceeded experimentally testing building blocks for quantum photonic operations between multiple photonic states generated with our quantum emitters: fusion gates. In these tests, I demonstrated a successful fusion of resource state from a quantum emitter: a first with this hardware platform and a key step towards the final goal of this project.

Complementing hardware development, the theoretical activities have focused on developing schemes to perform photonic operations specifically tailored for implementations with quantum emitters, a topic that was largely unexplored prior to this project. I investigated several aspects, including tools to analyze photonic quantum computing, the physical hardware requirements to reach fault-tolerance and enable practical applications for our photonic technology, and architectures that can ultimately enable photonic quantum computing suitable for quantum emitters.

Hardware development proceeded steadily and culminated in successfully implementing a key milestone for this project: the first programmable nonlinear quantum photonic circuit and its use in a proof-of-concept demonstration of quantum simulation of molecular quantum dynamics. The experiment demonstrated the capability to reprogram the nonlinear photonic circuits and implement protocols where strong nonlinearities are required. The usability of the programmable nonlinear photonic circuits is then used for one exemplary application of quantum simulation of the anharmonic molecular dynamics in the water molecule, successfully achieving the key goal of the project.

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)

Major results of the project, which surpassed the state of the art, are:

• The first interface between a quantum emitter and a low-loss programmable photonic chips in SiN and LNOI – enabling the developed technology to scale to complex circuits.
• The first demonstration of a photonic fusion with a quantum emitter – a key building block for photonic quantum computing.
• The first theoretical architectures for building photonic quantum computers with the developed technology.
• The first demonstration of programmable nonlinear quantum photonic circuits with quantum emitters and their use for quantum simulation of molecular dynamics.

These achievements represent significant progress in addressing target key barriers in the development of scalable quantum photonic hardware: a robust technology for implementing photon-photon interactions. Scaling this technology requires engineering the circuits to a large number of modes: an engineering problem which is now being targeted by companies that, following the exciting results produced in this project, are basing their technologies on the platform developed in QSUN (Sparrow Quantum in Denmark and ORCA Computing in UK).

Picture of the photonic chip interfaced with the quantum emitter