Only the size of a coin! Scientists demonstrate first fully integrated entangled quantum light source
Recently, an international research team from Leibniz University Hannover (Germany), the University of Twente (Netherlands) and the startup QuiX Quantum demonstrated for the first time an entangled quantum light source fully integrated on a chip.
The results of the study were published in the journal Nature Photonics.
Quantum bits (qubits) are the fundamental building blocks of quantum computers and the quantum Internet. Quantum light sources produce light qubits (photons) that can be used as quantum bits. Today, on-chip photonics has become the leading platform for handling the quantum state of light because it is compact and robust and can hold and arrange many elements on a single chip.
Today, light is guided on a chip through extremely compact structures that are used to build optical quantum computing systems. These are already available today through cloud computing.
Integrated photonics has recently emerged as a leading platform for implementing and processing optically entangled quantum states in compact, robust and scalable chip formats for applications in long-range quantum-secure communication, quantum-accelerated information processing and non-classical metrology.
However, the quantum light sources developed to date rely on external bulky excitation lasers, making them impractical prototype devices that cannot be reproduced - which hinders their scalability and movement out of the lab into real-world applications.
The key is "hybrid technology," which combines a laser made of indium phosphide, a filter and a cavity made of silicon nitride, and brings them together in a chip. On the chip, two photons are generated from a laser field in a spontaneous, nonlinear process. Each photon spans a range of colors at the same time, which is called "superposition," and the colors of the two photons are correlated, meaning that the photons are entangled and can store quantum information.
This time, the experimental team demonstrated a fully integrated quantum light source that overcomes these challenges by integrating a laser cavity, an efficient tunable noise suppression filter (>55dB) using the optical Vernier effect, and a nonlinear micromirror that generates entangled photon pairs through spontaneous four-wave mixing.
The entire quantum light source is mounted on a chip smaller than a one-euro coin. By using a novel "hybrid technique" that combines a laser made of indium phosphide and a filter made of silicon nitride on a single chip, the researchers have reduced the size of the source by more than 1,000 times.
The hybrid quantum source employs an electrically pumped indium phosphide (InP) gain section and a Si3N4 low-loss perturbation filter system, and demonstrates high-performance parameters, namely pair emission in four resonant modes in the telecom band (bandwidth ~1 terahertz) and a remarkable pair detection rate of ~620 Hz at a high coincidence-to-chance ratio of ~80. The source directly creates high-dimensional frequency bin entangled quantum states (qubits/qudits), which is verified by quantum interferometry with up to 96% visibility (violating Bell's inequality) and by density matrix reconstruction, showing up to 99% fidelity.
A laser-integrated photonic quantum light source with band entangled photon pairs
Performance characteristics of quantum light sources
This approach uses a hybrid photonic platform to achieve scalable, commercially viable, low-cost, compact, lightweight and field-deployable entangled quantum sources. They are key to practical applications outside the laboratory, such as in quantum processors and quantum satellite communication systems.
"Our breakthrough allows us to reduce the size of the source by more than a factor of 1,000, resulting in reproducibility, long-time stability, scalability and potential mass production." "All of these properties are needed for real-world applications, such as quantum processors," said Professor Michael Kues, director of the Institute of Photonics at Leibniz University Hannover and member of the board of PhoenixD, a cluster of excellence at Leibniz University Hannover.
From left: Prof. Dr. Michael Kues, PhD student Hatam Mahmudlu, Humboldt University researcher Dr. Raktim Haldar
"Now we can integrate the laser with the other components on the chip so that the entire quantum source is smaller than a one-euro coin. Our tiny device can be thought of as a step toward achieving quantum dominance with photons on a chip." Researcher Dr. Raktim Haldar said, "Unlike Google, which currently uses ultracold quantum bits in cryogenic systems, quantum dominance can be achieved with such photonic systems on a chip even at room temperature."
The scientists also expect their findings to help reduce production costs for applications. kues said, "We can imagine that our quantum light source will soon become an essential component of programmable photonic quantum processors."
Reference links:
[1] https://phys.org/news/2023-04-quantum-source-fully-on-chip-scalability.html
[2]https://www.nature.com/articles/s41566-023-01193-1
[3]https://spectrum.ieee.org/quantum-entanglement
