Pioneering Nonclassical Photon States
Executive Summary: At the University of Waterloo, researchers are breaking new ground in quantum optics, generating and detecting entangled photon triplets in superconducting parametric cavities. By integrating QuantWare’s Crescendo-S TWPA, the research team achieved the first-ever observation of tripartite entanglement in a non-Gaussian microwave field—opening new possibilities for quantum communication, computing, and sensing.
About the University of Waterloo
Rooted in a pioneering spirit since 1957, the University of Waterloo has grown from a small group of engineering students into one of the world’s foremost research-intensive institutions. By weaving together academic excellence and entrepreneurial drive—most notably through its signature cooperative education programs—Waterloo has built a reputation for turning cutting-edge theories into practical impact.
Today, at the Engineered Quantum Systems Laboratory (EQSL) within the Institute for Quantum Computing, the University is once again breaking new ground: pushing the boundaries of quantum optics and opening doors to next-generation quantum communication, computing, and sensing technologies.
Generating Entangled Photon Triplets
Microwave quantum optics is one of the main thrusts of EQSL. In MQO, they use superconducting quantum circuits to produce novel quantum states of light, studying their fundamental properties and applications. In a recent experiment, EQSL produced entangled photon triplets in a superconducting parametric cavity. This phenomenon, known as third-order spontaneous down-conversion, transforms a single high-energy photon into three entangled photons. These novel, highly nonclassical states of entangled photons could set the foundation for advanced quantum communication, computing, and sensing applications.
Ultra-low noise
Generating the photon triplets is, however, only part of the challenge. Detecting such weak signals requires extremely low-noise amplification, as conventional amplifiers frequently introduce noise that fully obscures the photons’ signatures. A near-quantum-limited TWPA is therefore essential for the job.
To validate that they were able to achieve the required ultra-low noise levels required for this experiment, the research team used a Shot Noise Tunnel Junction (SNTJ) in their experimental setup. This enabled absolute noise power calibration, a key requirement for detecting weak quantum signals with high fidelity.
Validating Triplet States
Noise suppression was paramount to this experiment’s success. By integrating the University’s advanced parametric cavity setup with QuantWare’s Crescendo-S TWPA, the researchers succeeded in observing signature properties of the triplet states—most notably Wigner negativity and genuine tripartite non-Gaussian entanglement. This was the first-ever demonstration of tripartite entanglement in a non-Gaussian microwave field, marking a significant step forward in continuous-variable quantum information.
Extremely Low Noise, Wide Bandwidth: “QuantWare’s near quantum-limited Crescendo-S TWPA enabled us to detect the states over a range of mode frequencies which we had been unable to detect in the past. The extremely low noise characteristics over a wide band of the Crescendo was an essential component for our successful results.”
Reduced Averaging Time: “Using QuantWare’s Crescendo-S has greatly reduced the length of each of our measurements because we require orders of magnitude less averaging thanks to the extremely low noise in the amplifier. This not only speeds up our experimental work but is an enabling feature.
By suppressing noise in these particularly low frequency ranges, QuantWare’s Crescendo-S played a pivotal role in validating the highly nonclassical photon states—demonstrating that the exploration of novel quantum phenomena is now within practical reach.
Implications for Quantum Research and Beyond
This demonstration brings a new degree of feasibility to continuous variable quantum information science, proving that entangled photon triplets can be harnessed as powerful resources for quantum communication, computing, and sensing.
Building on these findings, EQSL will expand its work in continuous variable quantum information and analog quantum simulation, continuing to rely on Crescendo-S for high-sensitivity measurements. The successful validation of these nonclassical states opens new opportunities in quantum-enhanced metrology, error correction, and secure quantum communication networks.
As the quantum field moves toward practical applications, the ability to generate and detect these states could contribute to next-generation quantum architectures and fault-tolerant systems, further bridging the gap between experimental quantum optics and scalable quantum computing.
For an in-depth look at this experiment and its findings, refer to the full study by the University of Waterloo.