Researchers at the Niels Bohr Institute (NBI) at the University of Copenhagen in Denmark have developed a tunable system that advances quantum sensing by improving accuracy and overcoming limits imposed by conventional optics-based sensing systems.
The development will help improve sensing technologies for biomedical and cosmic applications.
Optical sensing technology is widely used and is part of our everyday lives. Optical sensors are used everywhere, from CCTV cameras that can perform intrusion detection to sensors that help cars drive autonomously, performing minimally invasive surgeries, to object detection and quality control in large-scale industrial automation.
As technology improves, sensors have become smarter but also smaller and have rapidly begun reaching the quantum limit, where noise arising during measurements at the smallest of scales interferes with sensor operations. This is where quantum technologies step in to cancel or reduce the noise.
Entanglement, where quantum particles remain connected and their states are correlated irrespective of the distance between them, is a unique property in quantum physics. Researchers at NBI used large-scale entanglement to create a tunable quantum system.
How did they do it?
To develop such a system, researchers at NBI paired a multi-photon light state with a large atomic spin ensemble, marking the first such system anywhere in the world. Combining these two technologies enables frequency-dependent squeezing, which then helps reduce quantum noise across a wide frequency band.
‘Squeezing light’ helps reduce the quantum noise and can be achieved by reducing either the amplitude or phase of light. For a light squeeze to work across a broad frequency range, amplitude noise or phase reduction must also occur at different frequencies.
This is where the atomic spin ensemble helps, since it can rotate the phase of squeezed light depending on its own frequency. Additionally, the ensemble can also switch the sign of noise from negative to positive, which helps reduce back-action and detect the noise of the sensor.
Back action noise occurs when the measurement process creates disturbances in the system being measured, whereas detection noise is the uncertainty in the measurements made by the sensor.
Applications of the system
Frequency-dependent squeezing has already been applied in applications such as gravitational wave detectors, but it needs over 900 feet (300 m) long optical resonators to work. The research team achieved similar performance in this setup using a tabletop device.
“The sensor and the spin system interact with two entangled beams of light,” explained Eugene Polzik, a professor at NBI, who was involved in the work. “After the interaction, the two beams are detected, and the detected signals are combined. The result is broadband signal detection beyond the standard quantum limit of sensitivity.”
The researchers suggest that their tunable quantum sensing device could help detect changes in time, acceleration, and magnetic fields. In biomedical applications, the sensors could help improve magnetic resonance imaging (MRI) resolution for earlier detection of neurological disorders, the press release added.
The research findings were published in the journal Nature.