Prototype chip.
Quantum simulator on a single chip Effective quantum simulators could enable researchers to gain deeper insights into unresolved questions in physics. Researchers in the EPIQUS project are working to develop a quantum simulator on a single silicon chip, bringing together electronic, photonic and quantum components, as Dr Mher Ghulinyan explains. The energy of a given quantum system can be described by a set of equations called a Hamiltonian, which become extremely difficult to solve using classical or standard computers as the system complexity grows. This is where quantum simulators could play an important role, as they allow researchers to build an architecture which will work with ions, photons, semiconductor qubits or other quantum particles. “You can then design an architecture which is formally described by the same set of equations as your real system of interest,” explains Dr Mher Ghulinyan, a Senior Researcher at the Fondazione Bruno Kessler in Trento, Italy. The system of interest itself could be a low temperature physics problem, a chemical
reaction, or even a set of financial transactions, in fact anything that can be described by quantum rules. “You run your simulator and collect statistical data. You can run millions of simulations within few minutes and then reach a statistical result,” continues Dr Ghulinyan.
EPIQUS project As the coordinator of the EU-funded EPIQUS project, Dr Ghulinyan is part of a team working to develop a quantum simulator, which could prove to be an important tool across many fields of research. This research is still at a fairly early stage however, with Dr Ghulinyan and his colleagues exploring new ideas and novel concepts in their research. “We want to
bring together, on a single silicon chip, all the different components that we need to run an integrated, miniaturised quantum simulator operating at room temperature,” he outlines. A source of single photons is required for this, as well as a photonic integrated circuit that can be used to manipulate the photons and a detector to register their arrival, all on a single, portable chip. “On one side of the chip single photons are generated in silicon nitride (Si3N4) waveguides. This is done by a strong optical pump that comes from outside – it enters the waveguide as an intense laser pulse, which then interacts with the material,” says Dr Ghulinyan. This leads to a non-linear optical process called four wave mixing, and the generation of
Analog chip
A conceptual sketch of a quantum photonic chip.
Phase shifters
Si SPADs
Pulsed NIR DL
SiN waveguides
Coherent pump splitting
www.euresearcher.com
Scalable photon sources
Qubit manipulation
Photo-Detection & quenching circuits
45
Photonic chip testing set-up.
two new photons at two different wavelengths. These photons are entangled, as they have been created through the same unique process. “They are correlated with respect to their properties. You cannot have one without the other,” explains Dr Ghulinyan. Getting these photons to a detector is a significant technical challenge, for which researchers have developed a new process. “We have developed a very simple technological process, through which we are able to geometrically tilt the optical waveguide down towards the detector,” says Dr Ghulinyan. “This coupling between the photonic circuit and the electronic part – the detection – is essential. This is because we don’t lose photons like you would if you took them from a chip and used a fibre to go into an external detector. We go directly to the detector, which has already been fabricated in the substrate. These detectors operate at room temperature which in terms of cost-efficiency is a huge advantage over other detecting technologies which require cryogenic temperatures.” The waveguides themselves are pieces of silicon nitride with a width of around 600 nanometres and a height of 150 nanometres,
and they effectively guide the photons. Waveguides can have loops or corners with different angles, while Dr Ghulinyan and his team are also using a novel technology to realize phase shifters which can be used to manipulate photons and guide them in a certain direction. “A phase shifter modifies the phase of the optical wave, or the photon. This changes its properties so that it interacts with
This allows researchers to reconfigure the integrated optical circuit by running different currents through the phase shifters, thus changing the conditions of an experiment within a fraction of a second. The output of these experiments is collected through an array of Single Photon Avalanche Diodes (SPADs) – the detectors, which are then saved to the computer. “The computer can then plot a histogram of experiments, so you see a statistical distribution of the output of the waveguides. You can run millions of experiments a second,” says Dr Ghulinyan. This is a potentially powerful system, as Dr Ghulinyan explains. “Quantum simulators don’t do precise calculations, rather they predict a possible outcome of a quantum system. You can run millions of simulations and then gain a statistical result,” he outlines. “For example, you might be interested in a chemical reaction involving different raw materials, and you don’t know maybe what the result will be. You can then simulate this reaction using photons which interfere within waveguiding circuitries following the same governing rules as the electrons do in your real reaction.”
We want to bring together, on a single silicon chip, all the different components that we need to run an
integrated, miniaturised quantum simulator. the circuit in a different way,” he outlines. A phase shifter is a resistor, a tiny piece of metal, and when current flows through the material it heats up, causing a change in the refractive index. “When you change the refractive index, you change the refraction of the light and the path of the photon,” continues Dr Ghulinyan. “For example, if you have a y-junction you can use the phase shifters to direct the photons into one or the other arm differently and manipulate photons in that way.”
Quantum simulator The project consortium is working to make this a reality, with each of the partners bringing their own expertise to bear on the challenge of developing an effective quantum simulator. The consortium as a whole has all the expertise and technological skills required to build a fully integrated system, so Dr Ghulinyan says there is no need to bring in external partners. “We have access to a silicon microfabrication facility at FBK and the SPADs are a highly
EPIQUS Electronic-photonic integrated quantum simulator platform
Project Objectives
EPIQUS aims to demonstrate a cheap, easyto-use, performant Quantum Simulator (QS) based on full integration of silicon nitride photonics with silicon electronics. The core objective of EPIQUS is to set a cornerstone technology – demonstrate the first breakthrough device – which will simulate quantum mechanical problems in a compact device operating at ambient temperature.
Project Funding
EPIQUS has received funding from the European Commission - H2020 research and innovation programme under grant agreement No 899368. Integrated photonic circuit.
https://epiqus.fbk.eu/partners
sophisticated technology, the result of 30 years of development. We don’t need to send wafers to someone else to make integrated photonic circuits, and another for the single photon detectors. Everything involved with the chip is being fabricated here through a monolithic integration process,” he stresses. Alongside developing the integrated circuits and the electronics, researchers in the project are also considering the types of problems that could be studied using the fabricated chip. Some of the project partners provide ideas on what could be simulated, while the teams at the University of Vienna and University of Rostock are validating some ideas on different types of chips. “They do an experiment, a quantum simulation using laser written optical waveguide circuits and fibernetwork setups, and say; ‘ok, this architecture or this concept works. Let’s see if you can miniaturise it and put it on a single chip, with tiny waveguides’,” says Dr Ghulinyan. “We transfer these kinds of ideas to a very small, dense integrated circuit. We do the same experiment that was done on a fiber-network setup and validated as a concept, but this time we do it on a single chip.”
The project team is working to develop a demonstrator at a TRL of 4-5, although some of the individual components are closer to practical application. “Some of the FBK’s SPADS have been used on the international space station and CERN experiments, so they have a TRL of 8 or 9. We also do other integrated photonics for SMEs. We do small volume fabrications for some industrial contracts,” outlines Dr Ghulinyan. This is a highly complex area of research, with the partners working on different concepts and technologies which then need to be brought together. This can be a lengthy process, with researchers bringing together electronic, photonic and quantum technologies, yet Dr Ghulinyan says progress is being made. “We have produced some chips and are currently characterising them,” he outlines. There are also plans for a successor project, building on the progress that has been achieved so far in EPIQUS. “We hope to continue this research and conduct further experiments. We plan to work on the software to improve the performance of the system, and also explore new ideas on the quantum side of the concept,” continues Dr Ghulinyan. An optical image of a 1 cm wide photonic circuit.
46
EU Research
Project Partners
www.euresearcher.com
Contact Details
Project Coordination and Management Dr Mher Ghulinyan Fondazione Bruno Kessler via Sommarive, 18 38123 Trento, Italy T: +39 0461 314 676 E: ghulinyan@fbk.eu W: https://epiqus.fbk.eu M. Bernard, F. Acerbi, G. Paternoster, G. Piccoli, L. Gemma, D. Brunelli, A. Gola, G. Pucker, L. Pancheri, and M. Ghulinyan. Topdown convergence of near-infrared photonics with silicon substrate-integrated electronics. Optica 8, 1363-1364 (2021). https://doi.org/10.1364/OPTICA.441496 G Piccoli, M Sanna, M Borghi, L Pavesi, M Ghulinyan. Silicon oxynitride platform for linear and nonlinear photonics at NIR wavelengths. Optical Materials Express 12(9), 3551-3562 (2022). https://doi.org/10.1364/OME.463940 Neef, V., Pinske, J., Klauck, F., Teuber, L., Kremer, M., Ehrhardt, M., Heinrich, M., Scheel, S. and Szameit, A. Three-dimensional nonAbelian quantum holonomy. Nature Physics,19(1), pp.30-34 (2023). https://doi.org/10.1038/s41567-022-01807-5 Schiansky, P., Kalb, J., Sztatecsny, E., Roehsner, M.C., Guggemos, T., Trenti, A., Bozzio, M. and Walther, P. Demonstration of quantum-digital payments. Nature Communications 14, p. 3849 (2023). https://doi.org/10.1038/s41467-023-39519-w
Dr. Mher Ghulinyan
Dr. Mher Ghulinyan received the MS in 1995 and PhD in physics in 1999 from the Yerevan State University (Armenia). His early-career research at the University of Trento (2002-2006) focused on optical cavities and superlattices leading to first-time demonstrations of Bloch oscillations, Zener tunneling and Anderson localization of light. Moving to FBK in 2006, since then he works in the field of integrated classical and quantum photonics. Since 2020, he is coordinating the EU-funded research project “Electronic-photonic integrated quantum simulator platform” (EPIQUS).
47