The development of quantum information and quantum techniques allows researchers from various industries to limit statistical errors and enhance measurement precision. In contemporary times, there is a heavy demand for precision, as industry solutions and applications are in more demand for product accuracy and quality performance.
Quantum metrology is the study of individual packets of energy (called “quanta”) in order to generate standards of high-precision measurement and related research. Quantum metrology utilizes quantum effects and quantum mechanics in enhancing and limiting measurement precision. Researchers have found that quantum metrology is composed to two salient mechanisms: measuring physical parameters using classical physics and measuring quantum parameters using contemporary techniques.
Concepts in Quantum Metrology
Quantum metrology veers away from classical theories regarding measurement by providing advances in precise measurement that have not been considered in traditional theories. For instance, classical estimation theories (e.g. central limit theorem) would suggest that measurement errors may be reduced by utilizing an amount that is proportional to n-1/2. This occurs by repeating the measures by n number of times and then obtaining the mean of the result. In quantum metrology, the concept of the central limit theorem is made easier through the use of quantum effects such as entanglement, which limits the error for an amount that is proportional to 1/n.
While the practice of quantum metrology is bound by the assumption that there is an abundance of measurement data available for use, currently-existing frameworks and theories would suggest otherwise; nevertheless, contemporary studies on quantum metrology have proven the effectivity of the technique amidst lack of data or non-linear measurements. Techniques such as measuring quadratures or analyzing realistic measurements have been found useful in tempering the use of quantum metrology in order to further its use in applications where data is limited.
Quantum metrology is also perceived as a “triangle” that is composed of three quantum electrical standards, namely the Josephson voltage standard, the single-electron tunnelling current standard, and the quantum Hall resistance standard. These “legs” of the triangle have been the subject of extensive research in order to determine their universality, practical implications, and fundamental constants. Researchers have found that the single-electron leg may be the weakest among the three, suggesting the limited use of the variable in quantum studies.
Current Researches in Quantum Metrology
Classical measurement techniques have tried to conduct simultaneous quantum estimation of multiple parameters; all of these trials failed, leading theorists at the time to conclude that enabling such activity is impossible. The development of quantum metrology, however, allowed such process to take place. This led researchers to believe that the use of quantum metrology could make way for new mechanisms, applications, and innovations that would primarily involve multi-parameter quantum processes, such as the development of quantum technology in super computers or the understanding of quantum phase transitions. In another research, it was found that multi-parameter quantum technology could also improve electrical, gravitational, and magnetic imagery which all have scientific and technological implications.
Studies have also found that non-linear quantum metrology could provide better precision in measurement. For instance, a study utilized a spin-I nuclear magnetic resonance (NMR) ensemble in order to map significant quadratic interactions into the system. Results showed that better precision could be achieved by optimizing input states within the formula. The study also found that interferometric measurement with quadratic interaction could be utilized to measure quadrupolar coupling strength in an NMR system.
Future Directions in Quantum Metrology
Despite a significant number of contemporary researches in quantum metrology, researchers still perceive the field as an understudied area in scientific research. Current studies on quantum metrology are focused on determining the limits and applicability of the process in a variety of fields, including computing, imaging, and measurement applications. With the promise of more accurate means of measurement, quantum metrology is a field that has significantly garnered attention in the study of quantum physics.
Sources and Further Reading
- “Quantum metrology in the presence of limited data”, Cornell University, https://arxiv.org/abs/1810.12857.
- “Current status of the quantum metrology triangle”, Metrologia, https://www.researchgate.net/publication/228351874_Current_status_of_the_quantum_metrology_triangle.
- “Multi-parameter quantum metrology”, Advances in Physics: X, https://www.tandfonline.com/doi/full/10.1080/23746149.2016.1230476.
- “Quantum metrology”, IOP Science, https://iopscience.iop.org/article/10.1088/1674-1056/22/11/110601/pdf.
- “Advances in Quantum Metrology”, Cornell University, https://arxiv.org/abs/1102.2318.
- “Experimental demonstration of nonlinear quantum metrology with optimal quantum state”, Science Bulletin, https://www.sciencedirect.com/science/article/pii/S2095927318301208.