Experimental limitations such as optical loss and noise have prevented entanglement-enhanced measurements from demonstrating a significant quantum advantage in sensitivity. In a study, the Optics and Photonics Research Group at CU Boulder and their partners predict and demonstrate meaningful advances in fiber-based, quantum-enhanced remote sensing and probing of photosensitive materials.
The group modeled the internal loss, external phase noise, and inefficiency of a Mach-Zehnder interferometer. They used a practical fiber source that created Holland-Burnett entangled states from the two-mode squeezed vacuum. This showed the potential benefits of a quantum-based strategy for increasing sensitivity while greatly reducing internal loss and phase noise drawbacks.
The team discovered that compared to comparable entangled sources, a two-mode squeezed vacuum source emits around 25 times as many photons. They anticipated that phase sensitivity might rise as much as 28% above the shot noise limit.
Greg Krueger, a graduate student in the Optics and Photonics Research Group and first author on the paper, said, “In that moment, quantum physics became not something to just learn and work through, but to leverage and engineer to our advantage. Reading through the literature on entanglement-enhanced sensing revealed a substantial gap between seeing the physics in the lab and using those observations in a practical sensor. We wanted to explore what it would take to create such a sensor and how difficult that would be.”
The new work was unique in that it combined the effects of phase noise and optical losses into a single model, even though their impacts on classical and quantum versions of the sensor had previously been analyzed.
Krueger said, “Our findings highlight some subtle points on making a practical sensor using the general technique of entangled photon interferometry. We also drew attention to the open and largely unexplored idea of using these sensing methods with optical fiber sensors, which would greatly expand the range of applications for the technique.”
Assistant Research Professor Lior Cohen said, “Quantum mechanics‘ counterintuitive results inspired me. To continue this work, we have plans to develop quantum-enhanced, long-distance temperature sensors in fibers.”
The CU Boulder College of Engineering and Applied Science is committed to quantum research through its Quantum Engineering Initiative, which aims to build and expand research efforts in the field — especially in quantum sensing, which is a unique strength of the college — while developing and strengthening ties with local and regional partners. The Quantum Engineering Initiative recently opened a new interdisciplinary lab space dedicated to this effort.
- Gregory Krueger, Charles Yu, Stephen B. Libby, Robert Mellors, Lior Cohen, and Juliet T. Gopinath, “Realistic model of entanglement-enhanced sensing in optical fibers,” Opt. Express 30, 8652-8666 (2022). DOI: 10.1364/OE.451058