Scientists at the Niels Bohr Institute (NBI) have successfully overcome a significant hurdle in advancing the development of highly sensitive monitoring devices that rely on quantum technology.
Schematics of the experimental setup. a The spin ensemble is probed by linearly polarized off-resonant light with a top-hat spatial mode shape. The probe polarization angle α with respect to the x-axis is adjusted for the QND measurement of the collective atomic spin. A quarter- and a half-wave plate define the quadrature phase ϕ detected by the polarization homodyning. b When prepared in highly polarized (coherent spin) state, the atomic ensemble can be described as two-level system, thus exhibiting the behavior of a harmonic oscillator. Specifically, we can prepare the atomic oscillator with the effective negative mass, creating inverted spin population. c The effect of ponderomotive squeezing, originating from cross-correlations between QBAN and SN, can be interpreted as a virtual shift of the resonance frequency. Image Credit: Nature Communications (2023).
Exploring the heartbeat of an unborn child and conducting delicate medical examinations showcase the potential of quantum sensors.
Operating at the atomic scale, these sensors offer unprecedented accuracy compared to current technology. Researchers at the Niels Bohr Institute (NBI), University of Copenhagen, have successfully surmounted a major obstacle in developing quantum sensors.
Their findings have been published in the journal Nature Communications.
In the realm of life processes, minute changes in magnetic fields and tissue conductivity are ubiquitous. Quantum sensors excel at detecting these minuscule variations. However, a significant challenge lies in distinguishing relevant signals from various types of noise—a challenge that the NBI group has made strides in addressing.
Quantum sensors have become one of the first applications of nanotechnology. Our findings bring these sensors closer to applications. I expect we will see the first practical implementations in a couple of years.
Eugene Polzik, Study Lead Author and Professor, Niels Bohr Institute
In addition to monitoring heart anomalies, numerous other potential abnormalities can be examined—all while the patient remains undisturbed. Quantum sensors open the door to enhancing or enabling various examinations, including the monitoring of brain activity.
Hearing the Noise From the Quantum World
Quantum mechanics elucidates the behaviors of atoms, electrons, and photons, attributing not only specific physical properties to these particles but also defining their existence in particular states.
Quantum sensing initiates by preparing quantum states of light for signal reading. The quantum state of light engages with a probe quantum system, influenced by the forces or fields targeted for detection. Following the interaction, the light bears information on the measured quantity, allowing for highly accurate detection.
The engineering of the quantum probe system must be tailormade to fit the signal of interest. This is one of the main challenges for quantum sensing, since it is hard to eliminate unwanted noise completely.
Eugene Polzik, Study Lead Author and Professor, Niels Bohr Institute
Even after eliminating traditional sources of noise, such as electronic equipment in the room, the effects of quantum mechanics persist. In contrast to classical physics, quantum mechanics describes a particle's quantum state and other properties as a probability function or uncertainty.
One origin of quantum noise is the uncertainty related to the arrival of light particles (photons) at the detector, known as shot noise. Additionally, as photons transfer their momentum to the probe sensor, the interaction itself becomes a source of quantum noise, termed quantum backaction.
In their scientific article, the team presents a method to “listen” to the noise emanating from the quantum realm, enabling its removal and allowing the preservation of the real signal of interest.
Future Application in Astrophysics
Beyond medical examinations, magnetic quantum sensors have potential applications in various fields. One notable example is in the detection of gravitational waves. Initially proposed by Albert Einstein, the presence of cosmic gravitational waves is firmly established.
However, due to the relatively weak signature of gravitational waves compared to other cosmic signals, current methods for monitoring them require enhancement.
The integration of magnetic quantum sensors with gravitational wave antennas could offer a solution to the challenge of effectively monitoring gravitational waves. This, in turn, may contribute to a more profound understanding of the universe’s origin and evolution.
Journal Reference:
Jia, J., et al. (2023) Acoustic frequency atomic spin oscillator in the quantum regime. Nature Communications. doi.org/10.1038/s41467-023-42059-y.