Quantum sensors have been gaining popularity over the recent years, finding use in different safety-critical industries. This article defines the concept behind quantum sensing, its history, the current wide range of applications where quantum sensors are deployed, and the challenges they face.
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Consider a system in an n-dimensional space. In this system, a quantum state would be a vector that would consist of all the information about that system.
The benefit of a quantum state is that a system can be in diverse states simultaneously. As these quantum "environments" often change due to disturbances, quantum physics uses quantum sensors to measure and monitor their behavior.
History of Quantum Sensing
The earliest known records for quantum sensors can be found in the 1600's when Galileo used his own pulse and matched it with the swinging of the pendulum at the Pisa cathedral. He observed that each heartbeat marked that a specific time had passed. His heartbeat approximately matched one swing of the pendulum.
The concept of tick rate and time were the basis of this study and gave rise to atomic clocks. In an atomic clock, the natural oscillations of the atoms act as a pendulum. The only difference is that the oscillations of an atom have much higher frequencies and stability. Atomic clocks are entirely accurate, with an error of only 1 second in up to 100 million years.
Another use of quantum sensors can be found in atom interferometers, which exploit the quantum mechanical nature of the atom – including the protons and neutrons. The concept of an atom interferometer is simple: it uses interference between two waves in a space for measurement purposes. The idea, popularly known as interferometry, is commonly used in telecommunications, navigation, imaging, and construction.
The key idea behind an interferometer is that gravity influences a phase shift on an atomic matter wave, where this phase shift develops the modification of an interference pattern. Therefore, by measuring the shift in the gravitational pull of the atom, gravity is indirectly measured.
To achieve this, laser light is used to illuminate the atoms. If the atom absorbs light from the laser, it will lead to an increase in momentum and due to this, the atom will follow a separate path that it originally intended to follow. Once the light is absorbed and the interference pattern of the atoms recombines, the resultant difference provides us with the gravitational strength of the two paths.
The military initially used atom interferometers as systems like global positional systems (GPS) fail in untapped locations. The technology then found use in underwater oil and gas exploration as well as studying the seafloor.
Applications of Quantum Sensors Beyond Quantum Physics
Due to their high sensitivity, quantum sensors have been deployed in a wide range of critical operations. Areas such as renewable energy, nuclear energy, and geothermal energy have been adopting quantum sensors for their applications.
For instance, in nuclear power plants, quantum sensors have been deployed to aid in the nuclear energy output. Devices such as the atom interferometric quantum sensor are being used for detecting isotopes in nuclear energy plants.
Here, sensitive quantum sensors not only detect the amount of radiation in an isotope, but also help in remotely monitoring the safety of the nuclear power plant due to radiation.
As far as maintaining the manufacturing infrastructure is concerned, quantum sensors are used to detect early faults in equipment to obtain future performance diagnostic reports. Such an approach has replaced traditional time-based maintenance practices in with condition-based maintenance, reducing the overall cost and minimizing equipment failures.
Quantum sensors have also been increasingly deployed in electricity transmission grids, known as 'smart grids' where sensors monitor and analyze the performance. Factors such as temperature loss, strain, and stress in electrical power lines, useful indicators in determining electricity loss, are also measured. The input received by quantum sensor systems helps the electrical grid manufacturers to improve grid efficiency.
More recently, quantum sensors have been widely used in developing smart buildings. Quantum sensors accurately monitor the energy usage throughout the day in each building and based on that, the building functions such as ventilation, heating, and lighting are monitored. This helps reduce the overall energy consumption of the building, therefore consuming fewer resources.
The Future of Quantum Sensors
Despite their high sensitivity, quantum sensors are still prone to distinct types of noises, preventing their use in many applications. One hindering barrier is the lack of hardware available for actual sensing the parameters outside the laboratory setting, a common problem faced by advanced quantum technologies.
These restrictions create a domain gap between quantum physics research and actual environments. Scaling a quantum sensor to an industrial level is also challenging as quantum sensors are primarily designed for lab operations.
Factors such as quantum coherence, accompanied by environment loss and noise, also hinder the signal-to-noise ratio of the quantum sensors, such as those used in metrology applications.
As the global demand for advanced quantum technologies and quantum sensing rises, quantum sensors are likely to move from quantum theory experiments and become a mainstream, commercial quantum system.
While there are many challenges to be addressed before quantum sensors become commonplace, increased funding for quantum physics and industrial interest is sure to support the development of quantum sensing.
References and Further Reading
Crawford, S.E., Shugayev, R.A., Paudel, H.P., Lu, P., Syamlal, M., Ohodnicki, P.R., Chorpening, B., Gentry, R. and Duan, Y. (2021). Quantum Sensing for Energy Applications: Review and Perspective. Advanced Quantum Technologies, 4(8), p.2100049. https://doi.org/10.1002/qute.202100049
Degen, C. L., Reinhard, F. and Cappellaro, P. (2017). Quantum sensing. Reviews of Modern Physics, 89(3). https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.89.035002
www.chalmers.se. (2022) Quantum sensing | Chalmers. [online] Available at: https://www.chalmers.se/.
Association, Q.W. (2018). Quantum sensing. Medium. [online] Available at: https://medium.com/@quantum_wa/quantum-sensing-f33643d098bb.
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