Quantum Precision: The Untold Story of Metrology in India

Whenever we make a measurement, be it from a ruler, thermometer or a weighing scale, we tend to blindly trust the measurement device. But how do we know that it is accurate?

Whether you're filling your fuel tank, relying on GPS for navigation, or trusting your blood pressure monitor, a silent guardian ensures the accuracy of it all — metrology, the science of measurement. At the forefront of this in India is the CSIR-National Physical Laboratory (NPL), led by its current Director, Dr. Venu Gopal Achanta. Often overlooked outside the scientific community, metrology plays a crucial role in India’s economic, industrial and technological ecosystem.

This article dives into the significance of metrology in India, based on an in-depth interview with Dr. Venu Gopal, bringing out the hidden stories, challenges, and future of India’s national measurement framework.

NPL: India’s Backbone of Accuracy

As India’s only National Measurement Institute (NMI), the NPL serves as the ultimate authority for all measurement standards in the country. NPL is responsible for the realization, and dissemination of the SI units, such as the kilogram, metre, second, and kelvin. This forms the foundation of accurate and consistent measurements across sectors. It takes care of the testing and calibration of a wide array of instruments, ranging from industrial machinery and laboratory equipment to imported devices.

This role is of paramount importance across industries. For instance, in pharmaceuticals, minute deviations in the lab apparatus can affect drug efficacy and safety. In aerospace industries, sub-millimeter accuracy can be the difference between a successful launch and a catastrophic failure. In each case, the industrial equipment must be calibrated to NPL’s national standards, directly by NPL or indirectly through accredited laboratories.

Quality infrastructure for industries is voluntary across the world. However, there is a legal metrology framework under which the legal requirements for measuring instruments are enforced. NPL works with the legal metrology team to maintain traceability, meaning that the certification of the equipment is traceable to NPL even from the consumer level.

During COVID-19, NPL was one of the few laboratories that remained operational. It tested and calibrated critical devices like blood pressure monitors and digital thermometers. “We designed the digital thermometers, made them in house and transported them to various places,” adds Dr. Venu Gopal.

NPL’s role goes far beyond fundamental research; it’s deeply tied to industry and innovation. “The ‘I’ in ‘CSIR’ stands for ‘Industry,’ and we cater to about 4000 industries under metrology,” explains Dr. Venu Gopal. These include service projects, consultations, and testing for specific applications. For example, during COVID-19, numerous companies approached NPL with air purifier designs. NPL tested their safety, filtration, and noise levels, and helped redesign and improve the devices.

NPL also plays a vital role in India’s self-reliance (Atmanirbhar Bharat) by ensuring that products made in India can be calibrated, certified, and quality-tested within the country itself. This is achieved by developing Certified Reference Materials (CRMs) indigenously, which are standardized to Indian conditions of temperature, humidity etc. By doing so, NPL helps prevent the import of foreign reference materials, saving crores of rupees annually. While "Make in India" is important, the Director emphasizes that quality assurance matters even more, and metrology is what guarantees that quality.

IST and the Art of Measuring Time

Many would recall the series of "beeps" from the All India Radio (Akashvani) that announced the strike of the hour. What few know is that this was generated by NPL, which has been calibrating Indian Standard Time (IST) since the 1940s.

Today, the most common way to access IST is via the Network Time Protocol (NTP). This protocol allows computers to ping specific servers (like ntp.nplindia.res.in) and synchronize their clocks with IST using just a few kilobytes of data.

NTP provides millisecond-level accuracy, which is sufficient for daily tasks and internet synchronization. For more precise needs, Precision Time Protocol (PTP) is used, offering microsecond-level accuracy. At the highest level, space organizations like ISRO use Two-Way Satellite Time and Frequency Transfer (TWSTFT), which enables synchronization at the nanosecond level, critical for space missions.

The international body which generates the Coordinated Universal Time (UTC) is the BIPM (Bureau of International Weights and Measures). There are about 400 high-precision clocks from 90 locations around the world, which provide their data to BIPM. To minimize the impact of fluctuations, an ensemble average of the time signals is computed to generate the UTC. NPL contributes to this global ensemble and in return, receives monthly UTC data from BIPM. Using this information, NPL "steers" IST, adjusting its atomic clocks to remain tightly synchronized with UTC.

“Every 15 minutes, a signal is shared to BIPM via satellite to maintain high accuracy,” explains Dr. Achanta. NPL uses an ensemble of different atomic clocks like Cs fountain clocks, Rb clocks and H masers. By using a weighted average approach, NPL combines the outputs of all these clocks to generate IST that is both accurate and long-term stable.

This continuous process known as "clock seeding" involves regular calibration, synchronization, and correction. Recently, NPL has achieved a remarkable precision of just 1 nanosecond uncertainty in IST.

The Shift Toward Quantum Metrology Standards

Previously, the 7 SI units were based on physical prototypes (like a metal cylinder for kg) or properties of materials (like the triple point of water for Kelvin). But in 2019, the SI units were redefined based on fundamental constants of nature resulting in consistency and ultra-precise measurements. For example, the kilogram has been redefined in terms of the Planck constant. NPL has developed the ‘Kibble balance’ to measure kilogram to microgram level accuracy- a pursuit that took around 20 years of continual refinement.

The new SI system is largely based on the fixed physical laws, which paved the way for the quantum metrology standards. Quantum metrology uses principles of quantum mechanics to make ultra-precise measurements. Unlike traditional instruments, quantum metrology devices do not require external calibration as they work based on invariable quantum effects. This makes them capable of self-calibration. Scientists at NPL are currently working on designing and developing such robust quantum standards in India.

Environmental Metrology

NPL has recently set up Asia’s first calibration and certification facility for environmental monitoring equipment — crucial for accurate air quality indices and reporting of emissions. Furthermore, NPL operates a solar cell calibration laboratory, which is one of only five such recognized labs in the world. It is particularly notable for offering the lowest uncertainty in measuring short-circuit current, a key parameter in assessing the efficiency of solar cells.

Over the last three years, India has made a major leap in acoustic standards by becoming one of only three countries in the world to establish a full-range national standard for sound frequencies, covering 2 Hz to 20 kHz. This has applications in noise mapping, which helps assess and monitor noise pollution across cities. For the first time since the 1960s, NPL is conducting noise mapping of Delhi-NCR. According to India's environmental noise standards, any sound above 50 decibels (dB) is considered noise pollution. But today, even the quietest areas in Delhi-NCR exceed this threshold. The new data provided by NPL is already influencing policy decisions and triggering the formation of regulatory committees.

Other than that, NPL is also constantly contributing to Sustainable Development Goals (SDGs), through their research on clean water and sanitation, climate action etc.

Global Engagements and the Current Challenges

International collaboration and consensus play a huge role in metrology. Dr. Venu Gopal, as a member of the International Committee for Weights and Measures (CIPM) and The International Union of Pure and Applied Physics (IUPAP), has been representing India in the global forum. Having been elected to CIPM after 23 years from India, Dr. Venu Gopal has brought India to the forefront in the international engagements relating to metrology. He emphasizes on how such representation ensures that India’s perspective is heard on important global matters. For example, when a consultative committee was proposed to discuss environmental issues, India had advocated for the inclusion of third world countries in the same.

In many developed nations, there is seamless coordination between multiple institutions such as the metrology department, space agencies, and the telecom sector, allowing for collaboration, innovation and development. In India, however, achieving such coordination between multiple organisations becomes challenging. For example, India recently voted in favor of removing the leap second correction in global timekeeping standards, a critical decision discussed at CIPM. But implementing this change and translating it to telecom industries remains a challenge.

“The economy of a country is reflected directly in its metrology. Any top tier economy has a well-established metrology programme,” says Dr. Venu Gopal.

Countries like China and the United States invest millions of dollars into metrology annually, through institutions like NIST (National Institute of Standards and Technology). These investments not only improve precision in technology but also fuel industrial growth, thus boosting the economy. In contrast, India faces both financial constraints and administrative challenges.

Even under the National Quantum Mission (NQM), NPL did not receive funding, despite requests. Unlike countries where institutes are empowered to share resources and collaborate freely, NPL still faces challenges in funding and inter-agency coordination.

The Road Ahead

Looking ahead, Dr. Venu Gopal believes that the future of Indian metrology lies in recognizing its foundational role.  Leaders of scientific institutions must understand the importance of metrology and not view NPL as just another research institute, responsible for publishing papers in high-impact journals.  While scientific publishing is a part of NPL’s work, its broader responsibility lies in supporting the national metrology framework and enabling industries through precision science.

The Director underscores the importance of having state-of-the-art basic R&D facilities. A striking example came a few years ago, when a Korean group announced the discovery of room-temperature superconductivity — a potential scientific breakthrough. Within just ten days, NPL was able to reproduce the reported material, independently test it, and scientifically refute the claim, thanks to its well-maintained measurement systems. Over the next decade, NPL aims to expand these capabilities, develop quantum metrology standards, and modernize the equipment being used.

‘If you cannot measure it, you cannot control it’ said Lord Kelvin. Such is the profound importance of measurement in a world driven by innovation and development.  In this aspect, NPL has been a cornerstone to the nation’s metrology.

As India strides forward in space exploration, advanced manufacturing, green energy, and digital innovation, the demand for precision and reliability has never been higher. From calibrating the instruments that power our electric grids to developing quantum-based standards, NPL stands at the crossroads of science and industry.

The future of Indian science, industry, and policy will be measured, quite literally, by how well we continue to invest in and support this silent sentinel of accuracy.